LM2596 Datasheet

ON Semiconductor

Download PDF Datasheet

Datasheet

© Semiconductor Components Industries, LLC, 2008
November, 2008 Rev. 0
1Publication Order Number:
LM2596/D
LM2596
3.0 A, Step-Down Switching
Regulator
The LM2596 regulator is monolithic integrated circuit ideally suited
for easy and convenient design of a stepdown switching regulator
(buck converter). It is capable of driving a 3.0 A load with excellent
line and load regulation. This device is available in adjustable output
version and it is internally compensated to minimize the number of
external components to simplify the power supply design.
Since LM2596 converter is a switchmode power supply, its
efficiency is significantly higher in comparison with popular
threeterminal linear regulators, especially with higher input voltages.
The LM2596 operates at a switching frequency of 150 kHz thus
allowing smaller sized filter components than what would be needed
with lower frequency switching regulators. Available in a standard
5lead TO220 package with several different lead bend options, and
D2PAK surface mount package.
The other features include a guaranteed $4% tolerance on output
voltage within specified input voltages and output load conditions, and
$15% on the oscillator frequency. External shutdown is included,
featuring 80 mA (typical) standby current. Self protection features
include switch cyclebycycle current limit for the output switch, as
well as thermal shutdown for complete protection under fault
conditions.
Features
Adjustable Output Voltage Range 1.23 V 37 V
Guaranteed 3.0 A Output Load Current
Wide Input Voltage Range up to 40 V
150 kHz Fixed Frequency Internal Oscillator
TTL Shutdown Capability
Low Power Standby Mode, typ 80 mA
Thermal Shutdown and Current Limit Protection
Internal Loop Compensation
Moisture Sensitivity Level (MSL) Equals 1
PbFree Packages are Available
Applications
Simple HighEfficiency StepDown (Buck) Regulator
Efficient PreRegulator for Linear Regulators
OnCard Switching Regulators
Positive to Negative Converter (BuckBoost)
Negative StepUp Converters
Power Supply for Battery Chargers
See detailed ordering and shipping information in the package
dimensions section on page 23 of this data sheet.
ORDERING INFORMATION
1
5
TO220
TV SUFFIX
CASE 314B
1
5
Heatsink surface connected to Pin 3
TO220
T SUFFIX
CASE 314D
Pin 1. Vin
2. Output
3. Ground
4. Feedback
5. ON/OFF
D2PAK
D2T SUFFIX
CASE 936A
Heatsink surface (shown as terminal 6 in
case outline drawing) is connected to Pin 3
1
5
http://onsemi.com
See general marking information in the device marking
section on page 23 of this data sheet.
DEVICE MARKING INFORMATION
LM2596
http://onsemi.com
2
Figure 1. Typical Application and Internal Block Diagram
12 V
Unregulated
DC Input
L1
33 mH
GND
+Vin
1
Cin
100 mF3ON
/OFF5
Output
2
Feedback
4
D1
1N5822 Cout
220 mF
Typical Application (Adjustable Output Voltage Version)
Block Diagram
Unregulated
DC Input
+Vin
1
Cout
Feedback
4
Cin
L1
D1
R2
R1
Output
2
GND
3
ON/OFF
5
Reset
Latch
Thermal
Shutdown
150 kHz
Oscillator
1.235 V
Band-Gap
Reference
Freq
Shift
30 kHz
Comparator
Fixed Gain
Error Amplifier
Current
Limit
Driver
3.0 Amp
Switch
ON/OFF
3.1 V Internal
Regulator
Regulated
Output
Vout
Load
LM2596
5.0 V Regulated
Output 3.0 A Load
R1
R2
3.1k
1.0k
CFF
CFF
MAXIMUM RATINGS
Rating Symbol Value Unit
Maximum Supply Voltage Vin 45 V
ON/OFF Pin Input Voltage − −0.3 V V +Vin V
Output Voltage to Ground (SteadyState) − −1.0 V
Power Dissipation
Case 314B and 314D (TO220, 5Lead) PDInternally Limited W
Thermal Resistance, JunctiontoAmbient RqJA 65 °C/W
Thermal Resistance, JunctiontoCase RqJC 5.0 °C/W
Case 936A (D2PAK) PDInternally Limited W
Thermal Resistance, JunctiontoAmbient RqJA 70 °C/W
Thermal Resistance, JunctiontoCase RqJC 5.0 °C/W
Storage Temperature Range Tstg 65 to +150 °C
Minimum ESD Rating (Human Body Model: C = 100 pF, R = 1.5 kW)2.0 kV
Lead Temperature (Soldering, 10 seconds) 260 °C
Maximum Junction Temperature TJ150 °C
Stresses exceeding Maximum Ratings may damage the device. Maximum Ratings are stress ratings only. Functional operation above the
Recommended Operating Conditions is not implied. Extended exposure to stresses above the Recommended Operating Conditions may affect
device reliability.
LM2596
http://onsemi.com
3
PIN FUNCTION DESCRIPTION
Pin Symbol Description (Refer to Figure 1)
1 Vin This pin is the positive input supply for the LM2596 stepdown switching regulator. In order to minimize voltage transi-
ents and to supply the switching currents needed by the regulator, a suitable input bypass capacitor must be present
(Cin in Figure 1).
2 Output This is the emitter of the internal switch. The saturation voltage Vsat of this output switch is typically 1.5 V. It should be
kept in mind that the PCB area connected to this pin should be kept to a minimum in order to minimize coupling to
sensitive circuitry.
3 GND Circuit ground pin. See the information about the printed circuit board layout.
4 Feedback This pin is the direct input of the error amplifier and the resistor network R2, R1 is connected externally to allow pro-
gramming of the output voltage.
5 ON/OFF It allows the switching regulator circuit to be shut down using logic level signals, thus dropping the total input supply
current to approximately 80 mA. The threshold voltage is typically 1.6 V. Applying a voltage above this value (up to
+Vin) shuts the regulator off. If the voltage applied to this pin is lower than 1.6 V or if this pin is left open, the regulator
will be in the “on” condition.
OPERATING RATINGS (Operating Ratings indicate conditions for which the device is intended to be functional, but do not guarantee
specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics.)
Rating Symbol Value Unit
Operating Junction Temperature Range TJ40 to +125 °C
Supply Voltage Vin 4.5 to 40 V
LM2596
http://onsemi.com
4
SYSTEM PARAMETERS
ELECTRICAL CHARACTERISTICS Specifications with standard type face are for TJ = 25°C, and those with boldface type apply
over full Operating Temperature Range 40°C to +125°C
Characteristics Symbol Min Typ Max Unit
LM2596 (Note 1, Test Circuit Figure 15)
Feedback Voltage (Vin = 12 V, ILoad = 0.5 A, Vout = 5.0 V, ) VFB_nom 1.23 V
Feedback Voltage (8.5 V Vin 40 V, 0.5 A ILoad 3.0 A, Vout = 5.0 V) VFB 1.193
1.18
1.267
1.28
V
Efficiency (Vin = 12 V, ILoad = 3.0 A, Vout = 5.0 V) η73 %
Characteristics Symbol Min Typ Max Unit
Feedback Bias Current (Vout = 5.0 V) Ib25 100
200
nA
Oscillator Frequency (Note 2) fosc 135
120
150 165
180
kHz
Saturation Voltage (Iout = 3.0 A, Notes 3 and 4) Vsat 1.5 1.8
2.0
V
Max Duty Cycle “ON” (Note 4) DC 95 %
Current Limit (Peak Current, Notes 2 and 3) ICL 4.2
3.5
5.6 6.9
7.5
A
Output Leakage Current (Notes 5 and 6)
Output = 0 V
Output = 1.0 V
IL0.5
6.0
2.0
20
mA
Quiescent Current (Note 5) IQ5.0 10 mA
Standby Quiescent Current (ON/OFF Pin = 5.0 V (“OFF”))
(Note 6)
Istby 80 200
250
mA
ON/OFF PIN LOGIC INPUT
Threshold Voltage 1.6 V
Vout = 0 V (Regulator OFF) VIH 2.2
2.4
V
Vout = Nominal Output Voltage (Regulator ON) VIL 1.0
0.8
V
ON/OFF Pin Input Current
ON/OFF Pin = 5.0 V (Regulator OFF) IIH 15 30 mA
ON/OFF Pin = 0 V (regulator ON) IIL 0.01 5.0 mA
1. External components such as the catch diode, inductor, input and output capacitors can affect switching regulator system performance.
When the LM2596 is used as shown in the Figure 15 test circuit, system performance will be as shown in system parameters section.
2. The oscillator frequency reduces to approximately 30 kHz in the event of an output short or an overload which causes the regulated output
voltage to drop approximately 40% from the nominal output voltage. This self protection feature lowers the average dissipation of the IC by
lowering the minimum duty cycle from 5% down to approximately 2%.
3. No diode, inductor or capacitor connected to output (Pin 2) sourcing the current.
4. Feedback (Pin 4) removed from output and connected to 0 V.
5. Feedback (Pin 4) removed from output and connected to +12 V to force the output transistor “off”.
6. Vin = 40 V.
LM2596
http://onsemi.com
5
IQ, QUIESCENT CURRENT (mA)
40
TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 15)
V
out, OUTPUT VOLTAGE CHANGE (%)
V
out, OUTPUT VOLTAGE CHANGE (%)
, STANDBY QUIESCENT CURRENT (
TJ, JUNCTION TEMPERATURE (°C)
IO, OUTPUT CURRENT (A)
TJ, JUNCTION TEMPERATURE (°C)
Vin, INPUT VOLTAGE (V)
Vin, INPUT VOLTAGE (V)
INPUT - OUTPUT DIFFERENTIAL (V)
TJ, JUNCTION TEMPERATURE (°C)
Figure 2. Normalized Output Voltage
TJ, JUNCTION TEMPERATURE (°C)
Figure 3. Line Regulation
Figure 4. Dropout Voltage Figure 5. Current Limit
Figure 6. Quiescent Current Figure 7. Standby Quiescent Current
ILoad = 200 mA
ILoad = 3.0 A
Vin = 12 V
Vin = 40 V
L1 = 33 mH
Rind = 0.1 W
ILoad = 500 mA
ILoad = 3.0 A
Vout = 5.0 V
Measured at
Ground Pin
TJ = 25°C
VON/OFF = 5.0 V
μA)
1.0
0.6
0.2
0
-0.2
-0.4
-1.0
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
2.0
1.5
1.0
0.5
0
6.0
5.5
5.0
4.5
4.0
20
18
16
14
12
10
8.0
6.0
4.0
200
180
160
140
120
100
80
60
20
0
1251007550250-25-50 403530252015105.00
1251007550250-25-50 1251007550250-25-50
403530252015105.00 1251007550250-25-50
-0.8
-0.6
0.4
0.8 Vin = 20 V
ILoad = 500 mA
Normalized at TJ = 25°C
ILoad = 500 mA
TJ = 25°C
3.3 V and 5.0 V
12 V and 15 V
Istby
Vin = 25 V
LM2596
http://onsemi.com
6
Vsat, SATURATION VOLTAGE (V)
2.0
2.5
3.0
4.0
Ib, FEEDBACK PIN CURRENT (nA)
, STANDBY QUIESCENT CURRENT (μA)I stby
, INPUT VOLTAGE (V)
TJ, JUNCTION TEMPERATURE (°C)
SWITCH CURRENT (A)
NORMALIZED FREQUENCY (%)
TJ, JUNCTION TEMPERATURE (°C)
Figure 8. Standby Quiescent Current
Vin, INPUT VOLTAGE (V)
Figure 9. Switch Saturation Voltage
Figure 10. Switching Frequency Figure 11. Minimum Supply Operating Voltage
Figure 12. Feedback Pin Current
TJ = 25°C
200
180
140
120
100
80
60
40
20
0
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
5.0
4.5
3.5
1.5
1.0
0.5
0
40302520151050 0 0.5 1.0 1.5 2.0 3.0
1251007550250-25
-50
TJ, JUNCTION TEMPERATURE (°C)
100
80
60
40
20
0
-20
-40
-60
-80
-100 1251007550250-25-50
160
35 2.5
-40°C
25°C
125°C
Vout ' 1.23 V
ILoad = 500 mA
TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 15)
Vin
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
1.0
50 25 0 25 50 75 100 125
VIN = 12 V Normalized
at 25°C
LM2596
http://onsemi.com
7
2.0 A
0
0
A
B
C
100 ms/div2 ms/div
Figure 13. Switching Waveforms Figure 14. Load Transient Response
Vout = 5 V
A: Output Pin Voltage, 10 V/div
B: Switch Current, 2.0 A/div
C: Inductor Current, 2.0 A/div, ACCoupled
D: Output Ripple Voltage, 50 mV/div, ACCoupled
Horizontal Time Base: 5.0 ms/div
10 V
0
4.0 A
2.0 A
100 mV
Output
Voltage
Change
0
3.0 A
2.0 A
1.0 A
0
4.0 A
- 100 mV
Load
Current
TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 15)
D
Figure 15. Typical Test Circuit
D1
1N5822
L1
33 mH
Output
2
4
Feedback
Cout
220 mF
Cin
100 mF
LM2596
1
53ON
/OFFGND
Vin
Load
Vout
5,000 V
Adjustable Output Voltage Versions
Vout +Vrefǒ1.0 )R2
R1Ǔ
R2 +R1ǒVout
Vref
1.0Ǔ
Where Vref = 1.23 V, R1
between 1.0 k and 5.0 k
R2
R1
8.5 V - 40 V
Unregulated
DC Input
CFF
LM2596
http://onsemi.com
8
PCB LAYOUT GUIDELINES
As in any switching regulator, the layout of the printed
circuit board is very important. Rapidly switching currents
associated with wiring inductance, stray capacitance and
parasitic inductance of the printed circuit board traces can
generate voltage transients which can generate
electromagnetic interferences (EMI) and affect the desired
operation. As indicated in the Figure 15, to minimize
inductance and ground loops, the length of the leads
indicated by heavy lines should be kept as short as possible.
For best results, singlepoint grounding (as indicated) or
ground plane construction should be used.
On the other hand, the PCB area connected to the Pin 2
(emitter of the internal switch) of the LM2596 should be
kept to a minimum in order to minimize coupling to sensitive
circuitry.
Another sensitive part of the circuit is the feedback. It is
important to keep the sensitive feedback wiring short. To
assure this, physically locate the programming resistors near
to the regulator, when using the adjustable version of the
LM2596 regulator.
DESIGN PROCEDURE
Buck Converter Basics
The LM2596 is a “Buck” or StepDown Converter which
is the most elementary forwardmode converter. Its basic
schematic can be seen in Figure 16.
The operation of this regulator topology has two distinct
time periods. The first one occurs when the series switch is
on, the input voltage is connected to the input of the inductor.
The output of the inductor is the output voltage, and the
rectifier (or catch diode) is reverse biased. During this
period, since there is a constant voltage source connected
across the inductor, the inductor current begins to linearly
ramp upwards, as described by the following equation:
IL(on) +ǒVIN *VOUTǓton
L
During this “on” period, energy is stored within the core
material in the form of magnetic flux. If the inductor is
properly designed, there is sufficient energy stored to carry
the requirements of the load during the “off” period.
Figure 16. Basic Buck Converter
DVin RLoad
L
Cout
Power
Switch
The next period is the “off” period of the power switch.
When the power switch turns off, the voltage across the
inductor reverses its polarity and is clamped at one diode
voltage drop below ground by the catch diode. The current
now flows through the catch diode thus maintaining the load
current loop. This removes the stored energy from the
inductor. The inductor current during this time is:
IL(off) +ǒVOUT *VDǓtoff
L
This period ends when the power switch is once again
turned on. Regulation of the converter is accomplished by
varying the duty cycle of the power switch. It is possible to
describe the duty cycle as follows:
d+ton
T, where T is the period of switching.
For the buck converter with ideal components, the duty
cycle can also be described as:
d+Vout
Vin
Figure 17 shows the buck converter, idealized waveforms
of the catch diode voltage and the inductor current.
Power
Switch
Figure 17. Buck Converter Idealized Waveforms
Power
Switch
Off
Power
Switch
Off
Power
Switch
On
Power
Switch
On
Von(SW)
VD(FWD)
Time
Time
ILoad(AV)
Imin
Ipk
Diode Diode
Power
Switch
Diode VoltageInductor Current
LM2596
http://onsemi.com
9
PROCEDURE (ADJUSTABLE OUTPUT VERSION: LM2596)
Procedure Example
Given Parameters:
Vout = Regulated Output Voltage
Vin(max) = Maximum DC Input Voltage
ILoad(max) = Maximum Load Current
Given Parameters:
Vout = 5.0 V
Vin(max) = 12 V
ILoad(max) = 3.0 A
1. Programming Output Voltage
To select the right programming resistor R1 and R2 value (see
Figure 1) use the following formula:
Resistor R1 can be between 1.0 k and 5.0 kW. (For best
temperature coefficient and stability with time, use 1% metal
film resistors).
Vout +Vref ǒ1.0 )R2
R1Ǔ
R2 +R1ǒVout
Vref
*1.0Ǔ
where Vref = 1.23 V
1. Programming Output Voltage (selecting R1 and R2)
Select R1 and R2:
R2 = 3.0 kW, choose a 3.0k metal film resistor.
R2 +R1ǒVout
Vref *1.0Ǔ+ǒ5V
1.23 V *1.0Ǔ
Vout +1.23ǒ1.0 )R2
R1ǓSelect R1 = 1.0 kW
2. Input Capacitor Selection (Cin)
To prevent large voltage transients from appearing at the input
and for stable operation of the converter, an aluminium or
tantalum electrolytic bypass capacitor is needed between the
input pin +Vin and ground pin GND This capacitor should be
located close to the IC using short leads. This capacitor should
have a low ESR (Equivalent Series Resistance) value.
For additional information see input capacitor section in the
“Application Information” section of this data sheet.
2. Input Capacitor Selection (Cin)
A 100 mF, 50 V aluminium electrolytic capacitor located near
the input and ground pin provides sufficient bypassing.
3. Catch Diode Selection (D1)
A. Since the diode maximum peak current exceeds the
regulator maximum load current the catch diode current
rating must be at least 1.2 times greater than the maximum
load current. For a robust design, the diode should have a
current rating equal to the maximum current limit of the
LM2596 to be able to withstand a continuous output short.
B. The reverse voltage rating of the diode should be at least
1.25 times the maximum input voltage.
3. Catch Diode Selection (D1)
A. For this example, a 3.0 A current rating is adequate.
B. For robust design use a 30 V 1N5824 Schottky diode or
any suggested fast recovery diode in the Table 2.
LM2596
http://onsemi.com
10
PROCEDURE (ADJUSTABLE OUTPUT VERSION: LM2596) (CONTINUED)
Procedure Example
4. Inductor Selection (L1)
A. Use the following formula to calculate the inductor Volt x
microsecond [V x ms] constant:
B. Match the calculated E x T value with the corresponding
number on the vertical axis of the Inductor Value Selection
Guide shown in Figure 18. This E x T constant is a
measure of the energy handling capability of an inductor and
is dependent upon the type of core, the core area, the
number of turns, and the duty cycle.
C. Next step is to identify the inductance region intersected by
the E x T value and the maximum load current value on the
horizontal axis shown in Figure 18.
D. Select an appropriate inductor from Table 3.
The inductor chosen must be rated for a switching
frequency of 150 kHz and for a current rating of 1.15 x ILoad.
The inductor current rating can also be determined by
calculating the inductor peak current:
where ton is the “on” time of the power switch and
E T+ǒVIN *VOUT *VSATǓ
VOUT )VD
VIN *VSAT )VD
1000
150 kHz ǒV msǓ
Ip(max) +ILoad(max) )ǒVin *VoutǓton
2L
ton +Vout
Vin
x1.0
fosc
4. Inductor Selection (L1)
A. Calculate E x T [V x ms] constant:
B. E x T = 27 [V x ms]
C. ILoad(max) = 3.0 A
Inductance Region = L40
D. Proper inductor value = 33 mH
Choose the inductor from Table 3.
E T+ǒ12 *5*1.5Ǔ 5)0.5
12 *5)0.5 1000
150 kHz ǒV msǓ
E T+ǒ5.5Ǔ 5.5
7.5 6.6ǒV msǓ
5. Output Capacitor Selection (Cout)
A. Since the LM2596 is a forwardmode switching regulator
with voltage mode control, its open loop has 2pole1zero
frequency characteristic. The loop stability is determined by
the output capacitor (capacitance, ESR) and inductance
values.
For stable operation use recommended values of the output
capacitors in Table 1.
Low ESR electrolytic capacitors between 220uFand 1500uF
provide best results.
B. The capacitors voltage rating should be at least 1.5 times
greater than the output voltage, and often much higher
voltage rating is needed to satisfy low ESR requirement
5. Output Capacitor Selection (Cout)
A. In this example is recommended Nichicon PM
capacitors: 470 mF/35 V or 220 mF/35 V
6. Feedforward Capacitor (CFF)
It provides additional stability mainly for higher input voltages. For
Cff selection use Table 1. The compensation capacitor between
0.6 nF and 40 nF is wired in parallel with the output voltage setting
resistor R2, The capacitor type can be ceramic, plastic, etc..
6. Feedforward Capacitor (CFF)
In this example is recommended feedforward capacitor
15 nF or 5 nF.
LM2596
http://onsemi.com
11
LM2596 Series Buck Regulator Design Procedures (continued)
Table 1. RECOMMENDED VALUES OF THE OUTPUT CAPACITOR AND FEEDFORWARD CAPACITOR
(Iload = 3 A)
Nichicon PM Capacitors
Vin (V) Capacity/Voltage Range/ESR (mF/V/mW)
40 1500/35/24 1000/35/29 1000/35/29 680/35/36 560/25/55 560/25/55 470/35/46 470/35/46
26 1200/35/26 820/35 680/35/36 560/35/41 470/25/65 470/25/65 330/35/60
22 1000/35/29 680/35/36 560/35/41 330/25/85 330/25/85 220/35/85
20 820/35/32 470/35/46 470/25/65 330/25/85 330/25/85 220/35/85
18 820/35/32 470/35/46 470/25/65 330/25/85 330/25/85 220/35/85
12 820/35/32 470/35/46 220/35/85 220/25/111
10 820/35/32 470/35/46 220/35/85
Vout (V) 2 4 6 9 12 15 24 28
CFF (nF] 40 15 5 2 1.5 1 0.6 0.6
15uH
22uH
33uH
47uH
68uH
100uH
150uH
220uH
L35L27
L36
L27
L42 L43
L44
L37
L38
L30
L29
L21
L22
L31
L39
L40
L32
L23
L15
L24
L40
L40
L25
L34
0.6 0.8 1.0 1.5 2.0 2.5 3.0
4
5
6
7
8
9
10
15
20
25
30
40
50
60
70
E*T(V*us)
Maximum load current (A)
Figure 18. Inductor Value Selection Guides (For Continuous Mode Operation)
LM2596
http://onsemi.com
12
Table 2. DIODE SELECTION
VR
Schottky Fast Recovery
3.0 A 4.0 6.0 A 3.0 A 4.0 6.0 A
Through
Hole
Surface
Mount
Through
Hole
Surface
Mount
Through
Hole
Surface
Mount
Through
Hole
Surface
Mount
20 V 1N5820
MBR320P
SR302
SK32 1N5823
SR502
SB520
MUR320
31DF1
HER302
(all diodes
rated
to at least
100 V)
MURS320T3
MURD320
30WF10
(all diodes
rated
to at least
100 V)
MUR420
HER602
(all diodes
rated
to at least
100 V)
MURD620CT
50WF10
(all diodes
rated
to at least
100 V)
30 V 1N5821
MBR330
SR303
31DQ03
SK33
30WQ03
1N5824
SR503
SB530
50WQ03
40 V 1N5822
MBR340
SR304
31DQ04
SK34
30WQ04
MBRS340T3
MBRD340
1N5825
SR504
SB540
MBRD640CT
50WQ04
50 V MBR350
31DQ05
SR305
SK35
30WQ05
SB550 50WQ05
60 V MBR360
DQ06
SR306
MBRS360T3
MBRD360
50SQ080 MBRD660CT
NOTE: Diodes listed in bold are available from ON Semiconductor.
LM2596
http://onsemi.com
13
Table 3. INDUCTOR MANUFACTURERS PART NUMBERS
Inductance
(mH)
Current
(A)
Schott Renco Pulse Engineering Coilcraft
Through
Hole
Surface
Mount
Through
Hole
Surface
Mount
Through
Hole
Surface
Mount Surface Mount
L15 22 0.99 67148350 67148460 RL12842243 RL15002
2
PE53815 PE53815S DO3308223
L21 68 0.99 67144070 67144450 RL54715 RL15006
8
PE53821 PE53821S DO3316683
L22 47 1.17 67144080 67144460 RL54716PE53822 PE53822S DO3316473
L23 33 1.40 67144090 67144470 RL54717PE53823 PE53823S DO3316333
L24 22 1.70 67148370 67148480 RL12832243 PE53824 PE53825S DO3316223
L25 15 2.10 67148380 67148490 RL12831543 PE53825 PE53824S DO3316153
L26 330 0.80 67144100 67144480 RL54711PE53826 PE53826S DO5022P334
L27 220 1.00 67144110 67144490 RL54712PE53827 PE53827S DO5022P224
L28 150 1.20 67144120 67144500 RL54713PE53828 PE53828S DO5022P154
L29 100 1.47 67144130 67144510 RL54714PE53829 PE53829S DO5022P104
L30 68 1.78 67144140 67144520 RL54715PE53830 PE53830S DO5022P683
L31 47 2.20 67144150 67144530 RL54716PE53831 PE53831S DO5022P473
L32 33 2.50 67144160 67144540 RL54717PE53932 PE53932S DO5022P333
L33 22 3.10 67148390 67148500 RL12832243 PE53933 PE53933S DO5022P223
L34 15 3.40 67148400 67148790 RL12831543 PE53934 PE53934S DO5022P153
L35 220 1.70 67144170 RL54731PE53935 PE53935S
L36 150 2.10 67144180 RL54734PE54036 PE54036S
L37 100 2.50 67144190 RL54721PE54037 PE54037S
L38 68 3.10 67144200 RL54722PE54038 PE54038S DO5040H683ML
L39 47 3.50 67144210 RL54723PE54039 PE54039S DO5040H473ML
L40 33 3.50 67144220 67148290 RL54724PE54040 PE54040S DO5040H333ML
L41 22 3.50 67144230 67148300 RL54725PE54041 PE54041S DO5040H223ML
L42 150 2.70 67148410 RL54734PE54042 PE54042S
L43 100 3.40 67144240 RL54732PE54043 -
L44 68 3.40 67144250 RL54733PE54044 DO5040H683ML
LM2596
http://onsemi.com
14
APPLICATION INFORMATION
EXTERNAL COMPONENTS
Input Capacitor (Cin)
The Input Capacitor Should Have a Low ESR
For stable operation of the switch mode converter a low
ESR (Equivalent Series Resistance) aluminium or solid
tantalum bypass capacitor is needed between the input pin
and the ground pin, to prevent large voltage transients from
appearing at the input. It must be located near the regulator
and use short leads. With most electrolytic capacitors, the
capacitance value decreases and the ESR increases with
lower temperatures. For reliable operation in temperatures
below 25°C larger values of the input capacitor may be
needed. Also paralleling a ceramic or solid tantalum
capacitor will increase the regulator stability at cold
temperatures.
RMS Current Rating of Cin
The important parameter of the input capacitor is the RMS
current rating. Capacitors that are physically large and have
large surface area will typically have higher RMS current
ratings. For a given capacitor value, a higher voltage
electrolytic capacitor will be physically larger than a lower
voltage capacitor, and thus be able to dissipate more heat to
the surrounding air, and therefore will have a higher RMS
current rating. The consequence of operating an electrolytic
capacitor beyond the RMS current rating is a shortened
operating life. In order to assure maximum capacitor
operating lifetime, the capacitor’s RMS ripple current rating
should be:
Irms > 1.2 x d x ILoad
where d is the duty cycle, for a buck regulator
d+ton
T+Vout
Vin
and d +ton
T+
|Vout|
|Vout|)V
in
for a buck*boost regulator.
Output Capacitor (Cout)
For low output ripple voltage and good stability, low ESR
output capacitors are recommended. An output capacitor
has two main functions: it filters the output and provides
regulator loop stability. The ESR of the output capacitor and
the peaktopeak value of the inductor ripple current are the
main factors contributing to the output ripple voltage value.
Standard aluminium electrolytics could be adequate for
some applications but for quality design, low ESR types are
recommended.
An aluminium electrolytic capacitors ESR value is
related to many factors such as the capacitance value, the
voltage rating, the physical size and the type of construction.
In most cases, the higher voltage electrolytic capacitors have
lower ESR value. Often capacitors with much higher
voltage ratings may be needed to provide low ESR values
that, are required for low output ripple voltage.
Feedfoward Capacitor
(Adjustable Output Voltage Version)
This capacitor adds lead compensation to the feedback
loop and increases the phase margin for better loop stability.
For CFF selection, see the design procedure section.
The Output Capacitor Requires an ESR Value
That Has an Upper and Lower Limit
As mentioned above, a low ESR value is needed for low
output ripple voltage, typically 1% to 2% of the output
voltage. But if the selected capacitor’s ESR is extremely low
(below 0.05 W), there is a possibility of an unstable feedback
loop, resulting in oscillation at the output. This situation can
occur when a tantalum capacitor, that can have a very low
ESR, is used as the only output capacitor.
At Low Temperatures, Put in Parallel Aluminium
Electrolytic Capacitors with Tantalum Capacitors
Electrolytic capacitors are not recommended for
temperatures below 25°C. The ESR rises dramatically at
cold temperatures and typically rises 3 times at 25°C and
as much as 10 times at 40°C. Solid tantalum capacitors
have much better ESR spec at cold temperatures and are
recommended for temperatures below 25°C. They can be
also used in parallel with aluminium electrolytics. The value
of the tantalum capacitor should be about 10% or 20% of the
total capacitance. The output capacitor should have at least
50% higher RMS ripple current rating at 150 kHz than the
peaktopeak inductor ripple current.
LM2596
http://onsemi.com
15
Catch Diode
Locate the Catch Diode Close to the LM2596
The LM2596 is a stepdown buck converter; it requires a
fast diode to provide a return path for the inductor current
when the switch turns off. This diode must be located close
to the LM2596 using short leads and short printed circuit
traces to avoid EMI problems.
Use a Schottky or a Soft Switching
UltraFast Recovery Diode
Since the rectifier diodes are very significant sources of
losses within switching power supplies, choosing the
rectifier that best fits into the converter design is an
important process. Schottky diodes provide the best
performance because of their fast switching speed and low
forward voltage drop.
They provide the best efficiency especially in low output
voltage applications (5.0 V and lower). Another choice
could be FastRecovery, or UltraFast Recovery diodes. It
has to be noted, that some types of these diodes with an
abrupt turnoff characteristic may cause instability or
EMI troubles.
A fastrecovery diode with soft recovery characteristics
can better fulfill some quality, low noise design requirements.
Table 2 provides a list of suitable diodes for the LM2596
regulator. Standard 50/60 Hz rectifier diodes, such as the
1N4001 series or 1N5400 series are NOT suitable.
Inductor
The magnetic components are the cornerstone of all
switching power supply designs. The style of the core and
the winding technique used in the magnetic component’s
design has a great influence on the reliability of the overall
power supply.
Using an improper or poorly designed inductor can cause
high voltage spikes generated by the rate of transitions in
current within the switching power supply, and the
possibility of core saturation can arise during an abnormal
operational mode. Voltage spikes can cause the
semiconductors to enter avalanche breakdown and the part
can instantly fail if enough energy is applied. It can also
cause significant RFI (Radio Frequency Interference) and
EMI (ElectroMagnetic Interference) problems.
Continuous and Discontinuous Mode of Operation
The LM2596 stepdown converter can operate in both the
continuous and the discontinuous modes of operation. The
regulator works in the continuous mode when loads are
relatively heavy, the current flows through the inductor
continuously and never falls to zero. Under light load
conditions, the circuit will be forced to the discontinuous
mode when inductor current falls to zero for certain period
of time (see Figure 19 and Figure 20). Each mode has
distinctively different operating characteristics, which can
affect the regulator performance and requirements. In many
cases the preferred mode of operation is the continuous
mode. It offers greater output power, lower peak currents in
the switch, inductor and diode, and can have a lower output
ripple voltage. On the other hand it does require larger
inductor values to keep the inductor current flowing
continuously, especially at low output load currents and/or
high input voltages.
To simplify the inductor selection process, an inductor
selection guide for the LM2596 regulator was added to this
data sheet (Figure 18). This guide assumes that the regulator
is operating in the continuous mode, and selects an inductor
that will allow a peaktopeak inductor ripple current to be
a certain percentage of the maximum design load current.
This percentage is allowed to change as different design load
currents are selected. For light loads (less than
approximately 300 mA) it may be desirable to operate the
regulator in the discontinuous mode, because the inductor
value and size can be kept relatively low. Consequently, the
percentage of inductor peaktopeak current increases. This
discontinuous mode of operation is perfectly acceptable for
this type of switching converter. Any buck regulator will be
forced to enter discontinuous mode if the load current is light
enough.
HORIZONTAL TIME BASE: 2.0 ms/DIV
Figure 19. Continuous Mode Switching Current
Waveforms
VERTRICAL RESOLUTION 1.0 A/DIV
2.0 A
0 A
2.0 A
0 A
Inductor
Current
Waveform
Power
Switch
Current
Waveform
Selecting the Right Inductor Style
Some important considerations when selecting a core type
are core material, cost, the output power of the power supply,
the physical volume the inductor must fit within, and the
amount of EMI (ElectroMagnetic Interference) shielding
that the core must provide. The inductor selection guide
covers different styles of inductors, such as pot core, Ecore,
toroid and bobbin core, as well as different core materials
such as ferrites and powdered iron from different
manufacturers.
For high quality design regulators the toroid core seems to
be the best choice. Since the magnetic flux is contained
within the core, it generates less EMI, reducing noise
problems in sensitive circuits. The least expensive is the
bobbin core type, which consists of wire wound on a ferrite
rod core. This type of inductor generates more EMI due to
the fact that its core is open, and the magnetic flux is not
contained within the core.
When multiple switching regulators are located on the
same printed circuit board, open core magnetics can cause
LM2596
http://onsemi.com
16
interference between two or more of the regulator circuits,
especially at high currents due to mutual coupling. A toroid,
pot core or Ecore (closed magnetic structure) should be
used in such applications.
Do Not Operate an Inductor Beyond its
Maximum Rated Current
Exceeding an inductors maximum current rating may
cause the inductor to overheat because of the copper wire
losses, or the core may saturate. Core saturation occurs when
the flux density is too high and consequently the cross
sectional area of the core can no longer support additional
lines of magnetic flux.
This causes the permeability of the core to drop, the
inductance value decreases rapidly and the inductor begins
to look mainly resistive. It has only the DC resistance of the
winding. This can cause the switch current to rise very
rapidly and force the LM2596 internal switch into
cyclebycycle current limit, thus reducing the DC output
load current. This can also result in overheating of the
inductor and/or the LM2596. Different inductor types have
different saturation characteristics, and this should be kept
in mind when selecting an inductor.
0.4 A
0 A
0.4 A
0 A
Inductor
Current
Waveform
Power
Switch
Current
Waveform
Figure 20. Discontinuous Mode Switching Current
Waveforms
VERTICAL RESOLUTION 200 mA/DIV
HORIZONTAL TIME BASE: 2.0 ms/DIV
GENERAL RECOMMENDATIONS
Output Voltage Ripple and Transients
Source of the Output Ripple
Since the LM2596 is a switch mode power supply
regulator, its output voltage, if left unfiltered, will contain a
sawtooth ripple voltage at the switching frequency. The
output ripple voltage value ranges from 0.5% to 3% of the
output voltage. It is caused mainly by the inductor sawtooth
ripple current multiplied by the ESR of the output capacitor.
Short Voltage Spikes and How to Reduce Them
The regulator output voltage may also contain short
voltage spikes at the peaks of the sawtooth waveform (see
Figure 21). These voltage spikes are present because of the
fast switching action of the output switch, and the parasitic
inductance of the output filter capacitor. There are some
other important factors such as wiring inductance, stray
capacitance, as well as the scope probe used to evaluate these
transients, all these contribute to the amplitude of these
spikes. To minimize these voltage spikes, low inductance
capacitors should be used, and their lead lengths must be
kept short. The importance of quality printed circuit board
layout design should also be highlighted.
Unfiltered
Output
Voltage
Filtered
Output
Voltage
HORIZONTAL TIME BASE: 5.0 ms/DIV
Figure 21. Output Ripple Voltage Waveforms
VERTRICAL
Voltage spikes
caused by
switching action
of the output
switch and the
parasitic
inductance of the
output capacitor
RESOLUTION
20 mV/DIV
Minimizing the Output Ripple
In order to minimize the output ripple voltage it is possible
to enlarge the inductance value of the inductor L1 and/or to
use a larger value output capacitor. There is also another way
to smooth the output by means of an additional LC filter (20
mH, 100 mF), that can be added to the output (see Figure 30)
to further reduce the amount of output ripple and transients.
With such a filter it is possible to reduce the output ripple
voltage transients 10 times or more. Figure 21 shows the
difference between filtered and unfiltered output waveforms
of the regulator shown in Figure 30.
The lower waveform is from the normal unfiltered output
of the converter, while the upper waveform shows the output
ripple voltage filtered by an additional LC filter.
Heatsinking and Thermal Considerations
The ThroughHole Package TO220
The LM2596 is available in two packages, a 5pin
TO220(T, TV) and a 5pin surface mount D2PAK(D2T).
Although the TO220(T) package needs a heatsink under
most conditions, there are some applications that require no
heatsink to keep the LM2596 junction temperature within
the allowed operating range. Higher ambient temperatures
require some heat sinking, either to the printed circuit (PC)
board or an external heatsink.
The Surface Mount Package D2PAK and its
Heatsinking
The other type of package, the surface mount D2PAK, is
designed to be soldered to the copper on the PC board. The
copper and the board are the heatsink for this package and
the other heat producing components, such as the catch
diode and inductor. The PC board copper area that the
package is soldered to should be at least 0.4 in2 (or 260 mm2)
and ideally should have 2 or more square inches (1300 mm2)
of 0.0028 inch copper. Additional increases of copper area
beyond approximately 6.0 in2 (4000 mm2) will not improve
LM2596
http://onsemi.com
17
heat dissipation significantly. If further thermal
improvements are needed, double sided or multilayer PC
boards with large copper areas should be considered. In
order to achieve the best thermal performance, it is highly
recommended to use wide copper traces as well as large
areas of copper in the printed circuit board layout. The only
exception to this is the OUTPUT (switch) pin, which should
not have large areas of copper (see page 8 ‘PCB Layout
Guideline’).
Thermal Analysis and Design
The following procedure must be performed to determine
whether or not a heatsink will be required. First determine:
1. PD(max) maximum regulator power dissipation in the
application.
2. TA(max) maximum ambient temperature in the
application.
3. TJ(max) maximum allowed junction temperature
(125°C for the LM2596). For a conservative
design, the maximum junction temperature
should not exceed 110°C to assure safe
operation. For every additional +10°C
temperature rise that the junction must
withstand, the estimated operating lifetime
of the component is halved.
4. RqJC package thermal resistance junctioncase.
5. RqJA package thermal resistance junctionambient.
(Refer to Maximum Ratings on page 2 of this data sheet or
RqJC and RqJA values).
The following formula is to calculate the approximate
total power dissipated by the LM2596:
PD = (Vin x IQ) + d x ILoad x Vsat
where d is the duty cycle and for buck converter
d+ton
T+
VO
Vin
,
IQ(quiescent current) and Vsat can be found in the
LM2596 data sheet,
Vin is minimum input voltage applied,
VOis the regulator output voltage,
ILoad is the load current.
The dynamic switching losses during turnon and
turnoff can be neglected if proper type catch diode is used.
Packages Not on a Heatsink (FreeStanding)
For a freestanding application when no heatsink is used,
the junction temperature can be determined by the following
expression:
TJ = (RqJA) (PD) + TA
where (RqJA)(PD) represents the junction temperature rise
caused by the dissipated power and TA is the maximum
ambient temperature.
Packages on a Heatsink
If the actual operating junction temperature is greater than
the selected safe operating junction temperature determined
in step 3, than a heatsink is required. The junction
temperature will be calculated as follows:
TJ = PD (RqJA + RqCS + RqSA) + TA
where RqJC is the thermal resistance junctioncase,
RqCS is the thermal resistance caseheatsink,
RqSA is the thermal resistance heatsinkambient.
If the actual operating temperature is greater than the
selected safe operating junction temperature, then a larger
heatsink is required.
Some Aspects That can Influence Thermal Design
It should be noted that the package thermal resistance and
the junction temperature rise numbers are all approximate,
and there are many factors that will affect these numbers,
such as PC board size, shape, thickness, physical position,
location, board temperature, as well as whether the
surrounding air is moving or still.
Other factors are trace width, total printed circuit copper
area, copper thickness, single or doublesided, multilayer
board, the amount of solder on the board or even color of the
traces.
The size, quantity and spacing of other components on the
board can also influence its effectiveness to dissipate the heat.
Figure 22. Inverting BuckBoost Develops 12 V
D1
1N5822
L1
33 mH
Feedback
12 to 40 V
Unregulated
DC Input
Cin
100 mF/50 V GND
ON/OFF
+Vin
12 V @ 0.7 A
Regulated
Output
Cout
220 mF
LM2596ADJ
R3
R4
LM2596
http://onsemi.com
18
ADDITIONAL APPLICATIONS
Inverting Regulator
An inverting buckboost regulator using the
LM2596ADJ is shown in Figure 22. This circuit converts
a positive input voltage to a negative output voltage with a
common ground by bootstrapping the regulators ground to
the negative output voltage. By grounding the feedback pin,
the regulator senses the inverted output voltage and
regulates it.
In this example the LM259612 is used to generate a
12 V output. The maximum input voltage in this case
cannot exceed +28 V because the maximum voltage
appearing across the regulator is the absolute sum of the
input and output voltages and this must be limited to a
maximum of 40 V.
This circuit configuration is able to deliver approximately
0.7 A to the output when the input voltage is 12 V or higher.
At lighter loads the minimum input voltage required drops
to approximately 4.7 V, because the buckboost regulator
topology can produce an output voltage that, in its absolute
value, is either greater or less than the input voltage.
Since the switch currents in this buckboost configuration
are higher than in the standard buck converter topology, the
available output current is lower.
This type of buckboost inverting regulator can also
require a larger amount of startup input current, even for
light loads. This may overload an input power source with
a current limit less than 5.0 A.
Such an amount of input startup current is needed for at
least 2.0 ms or more. The actual time depends on the output
voltage and size of the output capacitor.
Because of the relatively high startup currents required by
this inverting regulator topology, the use of a delayed startup
or an undervoltage lockout circuit is recommended.
Using a delayed startup arrangement, the input capacitor
can charge up to a higher voltage before the switchmode
regulator begins to operate.
The high input current needed for startup is now partially
supplied by the input capacitor Cin.
It has been already mentioned above, that in some
situations, the delayed startup or the undervoltage lockout
features could be very useful. A delayed startup circuit
applied to a buckboost converter is shown in Figure 27.
Figure 29 in the “Undervoltage Lockout” section describes
an undervoltage lockout feature for the same converter
topology.
Design Recommendations:
The inverting regulator operates in a different manner
than the buck converter and so a different design procedure
has to be used to select the inductor L1 or the output
capacitor Cout.
The output capacitor values must be larger than what is
normally required for buck converter designs. Low input
voltages or high output currents require a large value output
capacitor (in the range of thousands of mF).
The recommended range of inductor values for the
inverting converter design is between 68 mH and 220 mH. To
select an inductor with an appropriate current rating, the
inductor peak current has to be calculated.
The following formula is used to obtain the peak inductor
current:
where ton +
|VO|
Vin )|VO|x1.0
fosc , and fosc +52 kHz.
Ipeak [
ILoad (Vin )|VO|)
Vin )
Vin xt
on
2L1
Under normal continuous inductor current operating
conditions, the worst case occurs when Vin is minimal.
Figure 23. Inverting BuckBoost Develops 12 V
D1
1N5822
L1
33 mH
Feedback
12 to 40 V
Unregulated
DC Input
Cin
100 mF/50 V GND
ON/OFF
+Vin
12 V @ 0.7 A
Regulated
Output
Cout
220 mF
LM2596ADJ
R3
R4
C1
0.1 mF
R2
47k
LM2596
http://onsemi.com
19
Figure 24. Inverting BuckBoost Regulator Shutdown
Circuit Using an Optocoupler
LM2596XX
1
35GN
D
ON/OFF
+Vin
R2
47 k
Cin
100 mF
NOTE: This picture does not show the complete circuit.
R1
47 k
R3
470
Shutdown
Input
MOC8101
-Vou
t
Off
On
5.0 V
0
+Vin
With the inverting configuration, the use of the ON/OFF
pin requires some level shifting techniques. This is caused
by the fact, that the ground pin of the converter IC is no
longer at ground. Now, the ON/OFF pin threshold voltage
(1.3 V approximately) has to be related to the negative
output voltage level. There are many different possible shut
down methods, two of them are shown in Figures 24 and 25.
Figure 25. Inverting BuckBoost Regulator Shutdown
Circuit Using a PNP Transistor
NOTE: This picture does not show the complete circuit.
R2
5.6 k
Q1
2N3906
LM2596XX
1
35GN
D
ON/OFF
R1
12 k -Vout
+Vin
Shutdown
Input
Off
On
+V
0
+Vin
Cin
100 mF
Negative Boost Regulator
This example is a variation of the buckboost topology
and it is called negative boost regulator. This regulator
experiences relatively high switch current, especially at low
input voltages. The internal switch current limiting results in
lower output load current capability.
The circuit in Figure 26 shows the negative boost
configuration. The input voltage in this application ranges
from 5.0 V to 12 V and provides a regulated 12 V output.
If the input voltage is greater than 12 V, the output will rise
above 12 V accordingly, but will not damage the regulator.
Figure 26. Negative Boost Regulator
D1
1N5822
L1
33 mH
Feedback
12 V
Unregulated
DC Input
Cin
100 mF/
50 V GND
ON/OFF
+Vin
12 V @ 0.7 A
Regulated
Output
LM2596ADJ
R3
R4
Cout
470 mF
Design Recommendations:
The same design rules as for the previous inverting
buckboost converter can be applied. The output capacitor
Cout must be chosen larger than would be required for a what
standard buck converter. Low input voltages or high output
currents require a large value output capacitor (in the range
of thousands of mF). The recommended range of inductor
values for the negative boost regulator is the same as for
inverting converter design.
Another important point is that these negative boost
converters cannot provide current limiting load protection in
the event of a short in the output so some other means, such
as a fuse, may be necessary to provide the load protection.
LM2596
http://onsemi.com
20
Delayed Startup
There are some applications, like the inverting regulator
already mentioned above, which require a higher amount of
startup current. In such cases, if the input power source is
limited, this delayed startup feature becomes very useful.
To provide a time delay between the time when the input
voltage is applied and the time when the output voltage
comes up, the circuit in Figure 27 can be used. As the input
voltage is applied, the capacitor C1 charges up, and the
voltage across the resistor R2 falls down. When the voltage
on the ON/OFF pin falls below the threshold value 1.3 V, the
regulator starts up. Resistor R1 is included to limit the
maximum voltage applied to the ON/OFF pin. It reduces the
power supply noise sensitivity, and also limits the capacitor
C1 discharge current, but its use is not mandatory.
When a high 50 Hz or 60 Hz (100 Hz or 120 Hz
respectively) ripple voltage exists, a long delay time can
cause some problems by coupling the ripple into the
ON/OFF pin, the regulator could be switched periodically
on and off with the line (or double) frequency.
Figure 27. Delayed Startup Circuitry
R1
47 k
LM2596XX
1
35GN
D
ON/OFF
R2
47 k
+Vin
+Vin
C1
0.1 mF
Cin
100 mF
NOTE: This picture does not show the complete circuit.
Undervoltage Lockout
Some applications require the regulator to remain off until
the input voltage reaches a certain threshold level. Figure 28
shows an undervoltage lockout circuit applied to a buck
regulator. A version of this circuit for buckboost converter
is shown in Figure 29. Resistor R3 pulls the ON/OFF pin
high and keeps the regulator off until the input voltage
reaches a predetermined threshold level with respect to the
ground Pin 3, which is determined by the following
expression:
Vth [VZ1 )ǒ1.0 )R2
R1ǓVBE (Q1)
Figure 28. Undervoltage Lockout Circuit for
Buck Converter
R2
10 k
Z1
1N5242B
R1
10 k
Q1
2N3904
R3
47 k
Vth 13 V
Cin
100 mF
LM2596XX
1
35GN
D
ON/OFF
+Vin
+Vin
NOTE: This picture does not show the complete circuit.
The following formula is used to obtain the peak inductor
current:
where ton +
|VO|
Vin )|VO|x1.0
fosc , and fosc +52 kHz.
Ipeak [
ILoad (Vin )|VO|)
Vin )
Vin xt
on
2L1
Under normal continuous inductor current operating
conditions, the worst case occurs when Vin is minimal.
Figure 29. Undervoltage Lockout Circuit for
BuckBoost Converter
R2
15 k
Z1
1N5242B
R1
15 k
Q1
2N3904
R3
47 k
Vth 13 V
Cin
100 mF
LM2596XX
1
35GN
D
ON/OFF
+Vin
+Vin
Vout
NOTE: This picture does not show the complete circuit.
Adjustable Output, LowRipple Power Supply
A 3.0 A output current capability power supply that
features an adjustable output voltage is shown in Figure 30.
This regulator delivers 3.0 A into 1.2 V to 35 V output.
The input voltage ranges from roughly 3.0 V to 40 V. In order
to achieve a 10 or more times reduction of output ripple, an
additional LC filter is included in this circuit.
LM2596
http://onsemi.com
21
Figure 30. 1.2 to 35 V Adjustable 3.0 A Power Supply with Low Output Ripple
D1
1N5822
L1
33 mH
Output
2
4
Feedback
R2
50 k
R1
1.21 k
L2
20 mHOutput
Voltage
1.2 to 35 V @ 3.0 A
Optional Output
Ripple Filter
40 V Max
Unregulated
DC Input
Cout
220 mFC1
100 mF
Cin
100 mF
LM2596Adj
1
53ON
/OFFGN
D
+Vin
LM2596
http://onsemi.com
22
THE LM2596 STEPDOWN VOLTAGE REGULATOR WITH 5.0 V @ 3.0 A OUTPUT POWER CAPABILITY.
TYPICAL APPLICATION WITH THROUGHHOLE PC BOARD LAYOUT
C1 100 mF, 50 V, Aluminium Electrolytic
C2 220 mF, 25 V, Aluminium Electrolytic
D1 3.0 A, 40 V, Schottky Rectifier, 1N5822
L1 33 mH, DO5040H, Coilcraft
R1 1.0 kW, 0.25 W
R2 3.0 kW, 0.25 W
Figure 31. Schematic Diagram of the 5.0 V @ 3.0 A StepDown Converter Using the LM2596ADJ
Vref = 1.23 V
R1 is between 1.0 k and 5.0 k
D1
1N5822
L1
33 mH
Output
2R2
3.0 k
R1
1.0 k
Regulated
Output Filtered
Vout2 = 5.0 V @ 3.0 A
Unregulated
DC Input
C2
220 mF
/16 V
C1
100 mF
/50 V
LM2596ADJ
1
53ON
/OFFGN
D
+Vin
+Vin = 10 V to 40 V
4 Feedback
Vout +Vref )ǒ1.0 )R2
R1Ǔ
ON/OFF
Figure 32. Printed Circuit Board Layout
Component Side
Figure 33. Printed Circuit Board Layout
Copper Side
NOTE: Not to scale. NOTE: Not to scale.
CFF
References
National Semiconductor LM2596 Data Sheet and Application Note
National Semiconductor LM2595 Data Sheet and Application Note
Marty Brown “Practical Switching Power Supply Design”, Academic Press, Inc., San Diego 1990
Ray Ridley “High Frequency Magnetics Design”, Ridley Engineering, Inc. 1995
LM2596
http://onsemi.com
23
ORDERING INFORMATION
Device Package Shipping
LM2596TADJG TO220
(PbFree)
50 Units / Rail
LM2596TVADJG TO220 (F)
(PbFree)
50 Units / Rail
LM2596DSADJG D2PAK
(PbFree)
50 Units / Rail
LM2596DSADJR4G D2PAK
(PbFree)
800 / Tape & Reel
For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging
Specifications Brochure, BRD8011/D.
A = Assembly Location
WL = Wafer Lot
Y = Year
WW = Work Week
G = PbFree Package
TO220
TV SUFFIX
CASE 314B
1
MARKING DIAGRAMS
5
TO220
T SUFFIX
CASE 314D
D2PAK
DS SUFFIX
CASE 936A
LM
2596TADJ
AWLYWWG
LM
2596TADJ
AWLYWWG
15
LM
2596ADJ
AWLYWWG
15
LM2596
http://onsemi.com
24
PACKAGE DIMENSIONS
TO220
TV SUFFIX
CASE 314B05
ISSUE L
V
Q
KF
UA
B
G
P
M
0.10 (0.254) P M
T
5X J
M
0.24 (0.610) T
OPTIONAL
CHAMFER
SLW
E
C
H
N
TSEATING
PLANE
NOTES:
1. DIMENSIONING AND TOLERANCING PER ANSI
Y14.5M, 1982.
2. CONTROLLING DIMENSION: INCH.
3. DIMENSION D DOES NOT INCLUDE
INTERCONNECT BAR (DAMBAR) PROTRUSION.
DIMENSION D INCLUDING PROTRUSION SHALL
NOT EXCEED 0.043 (1.092) MAXIMUM.
DIM MIN MAX MIN MAX
MILLIMETERSINCHES
A0.572 0.613 14.529 15.570
B0.390 0.415 9.906 10.541
C0.170 0.180 4.318 4.572
D0.025 0.038 0.635 0.965
E0.048 0.055 1.219 1.397
F0.850 0.935 21.590 23.749
G0.067 BSC 1.702 BSC
H0.166 BSC 4.216 BSC
J0.015 0.025 0.381 0.635
K0.900 1.100 22.860 27.940
L0.320 0.365 8.128 9.271
N0.320 BSC 8.128 BSC
Q0.140 0.153 3.556 3.886
S--- 0.620 --- 15.748
U0.468 0.505 11.888 12.827
V--- 0.735 --- 18.669
W0.090 0.110 2.286 2.794
5X D
TO220
T SUFFIX
CASE 314D04
ISSUE F
Q
12345
U
K
D
G
A
B1
5 PL
J
H
L
E
C
M
Q
M
0.356 (0.014) T
SEATING
PLANE
T
DIM MIN MAX MIN MAX
MILLIMETERSINCHES
A0.572 0.613 14.529 15.570
B0.390 0.415 9.906 10.541
C0.170 0.180 4.318 4.572
D0.025 0.038 0.635 0.965
E0.048 0.055 1.219 1.397
G0.067 BSC 1.702 BSC
H0.087 0.112 2.210 2.845
J0.015 0.025 0.381 0.635
K0.977 1.045 24.810 26.543
L0.320 0.365 8.128 9.271
Q0.140 0.153 3.556 3.886
U0.105 0.117 2.667 2.972
NOTES:
1. DIMENSIONING AND TOLERANCING PER ANSI
Y14.5M, 1982.
2. CONTROLLING DIMENSION: INCH.
3. DIMENSION D DOES NOT INCLUDE
INTERCONNECT BAR (DAMBAR) PROTRUSION.
DIMENSION D INCLUDING PROTRUSION SHALL
NOT EXCEED 10.92 (0.043) MAXIMUM.
B1 0.375 0.415 9.525 10.541
B
DETAIL A-A
B1
B
DETAIL AA
LM2596
http://onsemi.com
25
PACKAGE DIMENSIONS
D2PAK
D2T SUFFIX
CASE 936A02
ISSUE C
5 REF
A
123
K
B
S
H
D
G
C
E
ML
P
N
R
V
U
TERMINAL 6 NOTES:
1. DIMENSIONING AND TOLERANCING PER ANSI
Y14.5M, 1982.
2. CONTROLLING DIMENSION: INCH.
3. TAB CONTOUR OPTIONAL WITHIN DIMENSIONS A
AND K.
4. DIMENSIONS U AND V ESTABLISH A MINIMUM
MOUNTING SURFACE FOR TERMINAL 6.
5. DIMENSIONS A AND B DO NOT INCLUDE MOLD
FLASH OR GATE PROTRUSIONS. MOLD FLASH
AND GATE PROTRUSIONS NOT TO EXCEED 0.025
(0.635) MAXIMUM.
DIM
A
MIN MAX MIN MAX
MILLIMETERS
0.386 0.403 9.804 10.236
INCHES
B0.356 0.368 9.042 9.347
C0.170 0.180 4.318 4.572
D0.026 0.036 0.660 0.914
E0.045 0.055 1.143 1.397
G0.067 BSC 1.702 BSC
H0.539 0.579 13.691 14.707
K0.050 REF 1.270 REF
L0.000 0.010 0.000 0.254
M0.088 0.102 2.235 2.591
N0.018 0.026 0.457 0.660
P0.058 0.078 1.473 1.981
R5 REF
S0.116 REF 2.946 REF
U0.200 MIN 5.080 MIN
V0.250 MIN 6.350 MIN
__
45
M
0.010 (0.254) T
T
OPTIONAL
CHAMFER
8.38
0.33
1.016
0.04
16.02
0.63
10.66
0.42
3.05
0.12
1.702
0.067
SCALE 3:1 ǒmm
inchesǓ
*For additional information on our PbFree strategy and soldering
details, please download the ON Semiconductor Soldering and
Mounting Techniques Reference Manual, SOLDERRM/D.
SOLDERING FOOTPRINT*
ON Semiconductor and are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC reserves the right to make changes without further notice
to any products herein. SCILLC makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does SCILLC assume any liability
arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages.
“Typical” parameters which may be provided in SCILLC data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. All
operating parameters, including “Typicals” must be validated for each customer application by customer’s technical experts. SCILLC does not convey any license under its patent rights
nor the rights of others. SCILLC products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applications
intended to support or sustain life, or for any other application in which the failure of the SCILLC product could create a situation where personal injury or death may occur. Should
Buyer purchase or use SCILLC products for any such unintended or unauthorized application, Buyer shall indemnify and hold SCILLC and its officers, employees, subsidiaries, affiliates,
and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death
associated with such unintended or unauthorized use, even if such claim alleges that SCILLC was negligent regarding the design or manufacture of the part. SCILLC is an Equal
Opportunity/Affirmative Action Employer. This literature is subject to all applicable copyright laws and is not for resale in any manner.
LM2596/D
PUBLICATION ORDERING INFORMATION
N. American Technical Support: 8002829855 Toll Free
USA/Canada
Europe, Middle East and Africa Technical Support:
Phone: 421 33 790 2910
Japan Customer Focus Center
Phone: 81357733850
LITERATURE FULFILLMENT:
Literature Distribution Center for ON Semiconductor
P.O. Box 5163, Denver, Colorado 80217 USA
Phone: 3036752175 or 8003443860 Toll Free USA/Canada
Fax: 3036752176 or 8003443867 Toll Free USA/Canada
Email: orderlit@onsemi.com
ON Semiconductor Website: www.onsemi.com
Order Literature: http://www.onsemi.com/orderlit
For additional information, please contact your local
Sales Representative

Products

IC REG MULT CONFG ADJ 3A D2PAK-5
Available Quantity0
Unit Price2.19
IC REG MULT CONFG ADJ 3A TO220-5
Available Quantity0
Unit Price2.16
BOARD EVAL LM2596ADJ BUCK D2PAK
Available Quantity1
Unit Price52.53
IC REG MULT CONFG ADJ 3A TO220-5
Available Quantity0
Unit Price0