LTC4079 Datasheet by Analog Devices Inc.

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L7 LINE I “2 LTC4079 TECHNOLOGY L7 LJUW 1
LTC4079
1
4079f
For more information www.linear.com/LTC4079
Typical applicaTion
FeaTures DescripTion
60V, 250mA Linear Charger
with Low Quiescent Current
The LT C
®
4079 is a low quiescent current, high voltage
linear charger for most battery chemistry types including
Li-Ion/Polymer, Lead-Acid or NiMH battery stacks up to
60V. The maximum charge current is adjustable from
10mA to 250mA with an external resistor. The battery
charge voltage is set using an external resistor divider.
With an integrated power device, current sensing and
reverse current protection, a complete charging solution
using the LTC4079 requires very few external components.
Thermal regulation ensures maximum charge current up to
the specified limit without the risk of overheating. Charging
can be terminated by either C/10 or adjustable timer.
Input voltage regulation reduces charge current when
the input voltage falls to an adjustable level or the battery
voltage, making it well suited for energy harvesting
applications. Other features include temperature qualified
charging, bad battery detection, automatic recharge with
sampled feedback in standby for negligible battery drain,
and an open-drain CHRG status output. The device is
offered in a compact, thermally enhanced 10-lead (3mm
× 3mm) DFN package.
applicaTions
n Wide Input Voltage Range: 2.7V to 60V
n Adjustable Battery Voltage: 1.2V to 60V
n Adjustable Charge Current: 10mA to 250mA
n Low Quiescent Current While Charging: IIN = 4µA
n Ultralow Battery Drain When Shutdown or Charged:
IBAT < 0.01µA
n Auto Recharge
n Input Voltage Regulation for High Impedance Sources
n Thermal Regulation Maximizes Output Current
without Overheating
n Constant Voltage Feedback with ±0.5% Accuracy
n NTC Thermistor Input for Temperature Qualified
Charging
n Adjustable Safety Timer
n Charging Status Indication
n Thermally Enhanced 10-Lead (3mm × 3mm)
DFN Package
n Embedded Automotive and Industrial
n Backup Battery Charging from Another Battery
n Energy Harvesting Charger
n Thin Film Battery Products
L, LT , LT C , LT M , Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
Charging a Backup Battery
Li-Ion Battery Charge Cycle
+
IN
F 1.54M
249k
10k3.01k
10k Li-Ion
4079 TA01a
BAT9V TO 60V 8.4V
EN FB
CHRG FBG
PROG
T
NTCBIAS
TIMER NTC
GND
LTC4079
TIME (HOURS)
0
IBAT (mA)
VBAT (V)
80
100
120
6 73 4 5
4079 TA01b
60
40
1 2 8
20
0
140
8.0
8.2
8.4
7.8
7.6
7.4
7.2
8.6
VBAT
IBAT
500mAh 2-CELL LI-ION
C/10
TERMINATION
LTC4079
LTC4079
2
4079f
For more information www.linear.com/LTC4079
pin conFiguraTionabsoluTe MaxiMuM raTings
IN, BAT, EN, CHRG, FB, FBG Voltage .......... 0.3V to 62V
PROG TIMER Voltage .................................................. 3V
BAT Current....................................................... 400mA
PROG Current .....................................................–1.6mA
FBG Current .............................................................2mA
CHRG Current ..........................................................2mA
Operating Junction Temperature Range
(Notes 3, 5) ................................................ 40 to 125°C
Storage Temperature Range ......................65 to 150°C
(Notes 1, 2)
TOP VIEW
11
GND
DD PACKAGE
10-LEAD (3mm × 3mm) PLASTIC DFN
10
9
6
7
8
4
5
3
2
1BAT
FB
FBG
CHRG
TIMER
IN
EN
PROG
NTCBIAS
NTC
TJMAX = 125°C, θJA = 43°C/W
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
orDer inForMaTion
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LTC4079EDD#PBF LTC4079EDD#TRPBF LGNQ 10-Lead (3mm × 3mm) Plastic DFN –40°C to 125°C
LTC4079IDD#PBF LTC4079IDD#TRPBF LGNQ 10-Lead (3mm × 3mm) Plastic DFN –40°C to 125°C
Consult LT C Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Consult LT C Marketing for information on nonstandard lead based finish parts.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
LTC4079
LTC4079
3
4079f
For more information www.linear.com/LTC4079
elecTrical characTerisTics
The l denotes the specifications which apply over the specified operating junction temperature range, otherwise specifications are at
TA = 25°C (Notes 2, 3). VIN = 12V, VBAT = 7.4V, VFB = 1.057V, VEN = 12V, RPROG = 3k (100mA charge current) unless otherwise specified.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
VIN Operating Supply Voltage l2.7 60 V
VBAT Battery Voltage Range l60 V
VUVLO VIN Undervoltage Lockout VIN Rising
Hysteresis
l2.55
140
2.7 V
mV
VDUVLO Differential Undervoltage Lockout VIN-VBAT Rising
Hysteresis
l–20 15
80
50 mV
mV
VDVREG Differential Voltage Regulation Minimum VIN-VBAT for Charge Current l120 160 200 mV
IQ(IN) Input Supply Quiescent Current Charging (Note 4)
Charging Terminated (VFB = 1.210V)
Shutdown (EN = 0)
l
l
4
2
0.2
9
4
0.6
µA
µA
µA
IQ(BAT)Battery Drain Current Charging Terminated (VFB =1.210V)
Shutdown (EN = 0)
VIN = 0 or IN open
0.01
0.00
0.05
0.2
0.2
0.2
µA
µA
µA
Charging Functions
VFB(CHG) Feedback Pin Regulation Voltage in Constant-
Voltage Charge Mode
l
1.165
1.156
1.170
1.170
1.175
1.184
V
V
PROG Pin Regulated Voltage Constant-Current Mode 1.190 V
Ratio of BAT Current to PROG Pin Current 250 mA/mA
ICHG Battery Charge Current in Constant-Current
Mode (Note 5)
RPROG = 1.2k
RPROG = 3k
RPROG = 30k
l
l
l
236
93
8.5
248
99
10
260
105
11.5
mA
mA
mA
ITERMINATE Charging Termination Threshold RPROG = 1.2k
RPROG = 3k
RPROG = 30k
l
l
l
22
8.2
0.7
25
10
1
28
11.8
1.3
mA
mA
mA
tTERMINATE Deglitch Filter on C/10 Charge Termination ICHG Drops Below Termination Threshold 5 9 13 ms
tTIMER Safety Timer Accuracy –10 10 %
VRECHRG Recharge Threshold Voltage of FB Pin Relative to VFB(CHG) with VFB Falling 96.9 97.6 98.3 %
VFB(LOWBAT) Low Battery Threshold VFB for Low Battery Detection l0.780 0.800 0.820 V
Low Battery Time Out (Percentage of Safety
Timer)
Charging with VFB < VFB(LOWBAT) 18 %
RON Resistance of the Charge Path 5 Ω
IFB Feedback Pin Leakage VFB = 1.170V (in Regulation)
VFB = 8.4V (in Shutdown)
l
l
0.1
0.1
20
100
nA
nA
IFBG Feedback Ground Pin Leakage VFBG = 8.4V, EN = 0 l0.1 100 nA
RFBG Switch Resistance from FBG Pin to GND 160 Ω
Die Temperature (TJ) at Thermal Regulation 118 °C
LTC4079
LTC4079
4
4079f
For more information www.linear.com/LTC4079
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
NTC Temp Monitor
VCOLD Low Temp. Fault NTC Threshold Voltage VNTC/VNTCBIAS l72.3 73.8 75.3 %
VHOT High Temp. Fault NTC Threshold Voltage VNTC/VNTCBIAS l35.6 36.6 37.6 %
VNTC(DIS) NTC Disable Voltage Threshold VNTC l60 80 100 mV
Pulsed NTCBIAS Voltage 20k from NTCBIAS to Ground 4 V
NTCBIAS Period 3 Sec
NTCBIAS Pulse Width 210 µs
NTC Input Leakage Current VNTC = VNTCBIAS l0.1 100 nA
Enable Input (EN)
VEN(SD) Shutdown Threshold VEN Falling
Hysteresis
l0.400 0.750
55
1.100 V
mV
VEN(REG) Enable Pin Regulation Voltage Minimum VEN for Charge Current l1.170 1.190 1.210 V
Enable Pin Leakage Current When Pulled High VEN = 60V l0 20 nA
Status Outputs (CHRG)
Output Low Voltage 1mA Into the Open-Drain Output l0.16 0.4 V
Output Leakage Current VCHRG = 60V, VEN = 0V l0.1 100 nA
elecTrical characTerisTics
The l denotes the specifications which apply over the specified operating junction temperature range, otherwise specifications are at
TA = 25°C (Notes 2, 3). VIN = 12V, VBAT = 7.4V, VFB = 1.057V, VEN = 12V, RPROG = 3k (100mA charge current) unless otherwise specified.
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: Unless otherwise specified, current into a pin is positive and
current out of a pin is negative.
Note 3: The LTC4079 is tested under pulsed load conditions such that
TJ ≈ TA. The LTC4079E is guaranteed to meet performance specifications
from 0°C to 125°C junction temperature. Specifications over the –40°C
to 125°C operating junction temperature range are assured by design,
characterization and correlation with statistical process controls. The
LTC4079I is guaranteed over the full –40°C to 125°C operating junction
temperature range. Note that the maximum ambient temperature
consistent with these specifications is determined by specific operating
conditions in conjunction with board layout, the rated package thermal
impedance and other environmental factors.
Note 4: BAT pin charge current, PROG pin and feedback divider currents
are excluded from supply quiescent current.
Note 5: Charge current is reduced by thermal regulation as the junction
temperature rises above TLIM (118°C).
LTC4079 w \ \ L7 LJUW 5
LTC4079
5
4079f
For more information www.linear.com/LTC4079
Typical perForMance characTerisTics
Input Supply Quiescent Current
vs Temperature
Input Supply Quiescent Current
vs Supply Voltage
Battery Quiescent Current
vs Temperature
Battery Quiescent Current
vs Battery Voltage
Battery Charge Current
vs Battery Voltage
Battery Charge Current
vs Temperature
Regulated Feedback Voltage
vs Temperature
Regulated Feedback Voltage
vs VIN
Load Regulation of Regulated
Feedback Voltage
VIN = 12V, TA = 25°C unless otherwise noted.
VIN (V)
0
0
IIN (µA)
1
2
3
4
5
10 20 30 40
4079 G05
50 60
CHARGING
SHUTDOWN (EN = 0)
STANDBY
(CHARGING TERMINATED)
VFB = 1.2V
(IBAT = 0)
TEMPERATURE (°C)
50
0
IBAT (mA)
50
100
150
200
0 50 100 150
4079 G09
250
300
25 25 75 125
VIN = 12V
VBAT = 8.4V
ONSET OF THERMAL
REGULATION
RPROG = 1.2k
RPROG = 3k
RPROG = 30k
TEMPERATURE (°C)
50
0
IIN (µA)
1
2
3
4
0 50 100 150
4079 G04
5
6
25 25 75 125
CHARGING
SHUTDOWN (EN = 0)
STANDBY
(CHARGING TERMINATED)
VFB = 1.2V
(IBAT = 0)
TEMPERATURE (°C)
–50
0
IBAT (µA)
0.05
0.10
0.15
0.20
–25 0 25 50
4079 G06
75 100 125 150
VBAT = 8.4V
CHARGING TERMINATED
OR SHUTDOWN
TEMPERATURE (°C)
50
1.158
VFB(CHG) (V)
1.162
1.166
1.170
1.174
0 50 100 150
4079 G01
1.178
1.182
25 25 75 125
ONSET OF
THERMAL REGULATION
INTERNAL REFERENCE
VIN (V)
0
1.158
VFB(CHG) (V)
1.162
1.166
1.170
1.174
20 40 60
4079 G02
1.178
1.182
10 30 50
IBAT (mA)
0
1.158
VFB(CHG) (V)
1.162
1.166
1.170
1.174
100 200 250
4079 G03
1.178
1.182
50 150
RPROG = 1.2k
ICHG = 248mA
0
0
IBAT (nA)
10
20
30
40
20 40 60
4079 G07
50
60
10 30
VBAT (V)
50
SHUTDOWN (EN = 0)
STANDBY
(CHARGING TERMINATED)
0
IBAT (mA)
20
40
60
80
0246810
4079 G08
100
120
RPROG = 30k
RPROG = 3k
VBAT (V)
VFB(CHG) = 8.4V
LTC4079 VEM \ \ \ DHWC R (DROP i i I l \ \ \ \ x x \\ \ \ \ \ \ I 7V / / \l // // iii, v ‘E ’/ V \ \ / / \ // 6 L7HCU§QB
LTC4079
6
4079f
For more information www.linear.com/LTC4079
Charge Path Dropout Resistance
vs Temperature
Switch Resistance from
FBG to GND vs Temperature
EN and FB Pin Leakages
vs Temperature
NTCBIAS Period and Pulse Width
vs Temperature
Charge Path Dropout Resistance
vs VIN
Normalized Timer Duration
vs Temperature
Battery Charge Current vs VEN
Battery Charge Current
vs VIN – VBAT IBAT /IPROG Ratio vs IB AT
Typical perForMance characTerisTics
VIN = 12V, TA = 25°C unless otherwise noted.
0
IBAT (mA)
20
40
60
80
1.18 1.19 1.12 1.21 1.22
4079 G10
100
120
RPROG = 30k
RPROG = 3k
VEN (V)
0
IBAT (mA)
20
40
60
80
0.0 0.1 0.2 0.3 0.4 0.5 0.6
4079 G11
100
120
RPROG = 30k
OHMIC REGION
(DROPOUT)
RPROG = 3k
VIN – VBAT (V)
210
IBAT/IPROG (mA/mA)
220
240
230
250
260
270
0 50 100 150 200 250
4079 G12
280
290
4 DEVICES TESTED
RPROG = 1.2k
IBAT (mA)
TEMPERATURE (°C)
50
0
RON (Ω)
5
10
15
0 50 100 150
4079 G13
20
25
25 25 75 125
THERMAL REGULATION
VIN = 5.0V
VIN = 2.7V
PULSED LOAD (TJ ≈TA)
VIN – VBAT = 0.6V
RPROG = 1.2k
VIN (V)
0
0
RON (Ω)
2
4
6
20 40 60
8
10
10 30 50
PULSED LOAD (TJ ≈TA)
VIN – VBAT = 0.6V
RPROG = 1.2k
TEMPERATURE (°C)
50
0
LEAKAGE CURRENT (nA)
5
10
15
0 50 100 150
4079 G15
20
25 25 75 125
PIN AT 1.2V
PIN AT 60V
TEMPERATURE (°C)
50
0
RFBG (Ω)
50
100
150
0 50 100 150
4079 G16
200
250
300
350
25 25 75 125
TEMPERATURE (°C)
50
0.8
TIMER DURATION (RELATIVE TO 25°C)
0.9
1.0
1.1
0 50 100 150
4079 G17
1.2
25 25 75 125
TEMPERATURE (°C)
50
2.6
2.7
2.8
PERIOD (s)
2.9
3.0
3.1
0 50 100 150
4079 G18
3.2
200
210
220
PULSE WIDTH (µs)
230
240
250
260
25 25 75 125
PERIOD
PULSE WIDTH
LTC4079
LTC4079
7
4079f
For more information www.linear.com/LTC4079
pin FuncTions
IN (Pin 1): Input Supply Pin. This input provides power
to the battery charger. Bypass this pin with a ceramic
capacitor of at least 1µF.
EN (Pin 2): Enable Input. Charge current starts flowing
when this input rises above 1.190V, its regulation threshold.
When using a current limited power source, connect this
input to an external resistor divider from IN to GND to avoid
UVLO oscillations. This configuration can also be used
to maintain the source voltage (IN pin) at the maximum
power threshold (e.g., for solar panel). Pulling this pin
below 0.750V shuts down the device. This pin should
not be left floating.
PROG (Pin 3): Charge Current Program Pin. The current
out of this pin is 1/250th of the current out of the BAT
pin. A resistor connected from PROG to ground sets the
charge current in constant-current mode. This pin servos
to 1.190V during constant-current charging. Do not leave
this pin open. Limit parasitic capacitance on this node to
less than 50pF.
NTCBIAS (Pin 4): NTC Thermistor Bias Output. Connect
a low drift bias resistor from NTCBIAS to NTC pin, and
a thermistor from NTC pin to GND. The value of the bias
resistor is typically equal to the nominal resistance of
the thermistor at 25°C. Minimize parasitic capacitance
on this pin.
NTC (Pin 5): Input to the Battery Temperature Sense
Circuit. Connect the NTC pin to a negative temperature
coefficient (NTC) thermistor, which is typically co-packaged
with the battery, to signal the charger if the battery is too
hot or too cold to charge. The room temperature value
of the thermistor should be at least 2kΩ. If the battery’s
temperature is out of range, charging is paused until the
battery temperature re-enters the valid range. Connect a
1%, low drift bias resistor from NTCBIAS to NTC and a
thermistor from NTC to ground. Minimize parasitic ca-
pacitance on this pin. Tie the NTC pin to GND to disable
battery temperature sensing.
TIMER (Pin 6): Timer Capacitor Input. A capacitor on this
pin sets the maximum duration for battery charging from
charger enable or from the beginning of a recharge cycle.
For maximum charge duration of tTIMER (in Hours), the
required capacitance value can be determined as follows:
CTIMER = (tTIMER • 18.2nF/Hr)
A typical value of CTIMER is 100nF which terminates the
charge cycle after 5½ hours. Minimize leakage on this pin
to maintain timer accuracy.
The timer is disabled when this pin is tied to GND. In this
case charging terminates when the charge current falls
below 1/10th of the programmed charge current ICHG.
CHRG (Pin 7): Open-Drain Charge Status Output. Typically
pulled up to a voltage source through a resistor or a low
power LED and a resistor. This pin is pulled low by an
internal NMOS when LTC4079 is charging the battery.
The pin goes to high impedance when the charge current
drops below 1/10th of the programmed current, or the
charge cycle is timer terminated.
FBG (Pin 8): Ground Reference for Battery Voltage Divider.
This pin is connected to ground internally through an NMOS
switch when the battery is charging and disconnects the
battery voltage divider from GND when it is not needed.
When sensing the battery voltage the NMOS switch
presents a low resistance (RFBG =160Ω) to GND.
FB (Pin 9): Sense Pin for Divided Battery Voltage. This pin
servos to 1.170V (VFB(CHG)) during the constant-voltage
phase of the battery charge algorithm. The battery charge
voltage is set by using an appropriate resistor divider
from BAT to FB to FBG. Minimize leakage and parasitic
capacitance on this pin.
BAT (Pin 10): Battery Charger Output. This pin provides
charge current to the battery.
GND (Exposed Pad Pin 11): Ground. The exposed pad
must be soldered to a continuous ground plane of the
printed circuit board for electrical connection and the rated
thermal performance.
LTC4079 L7 LINE/“2
LTC4079
8
4079f
For more information www.linear.com/LTC4079
block DiagraM
+
2
10
CC/CV REGULATION,
EN REGULATION,
VIN-VBAT REGULATION
THERMAL REGULATION
CONTROL
RECHARGE
REFERENCE
+
IBAT
250
UVLO,
DIFF UVLO
OSC
BG REF
EN
CHRG
1IN
P1
BAT
9
FB
5
6
NTC
TIMER
3
PROG
CTIMER
RBIAS
4079 F01
RPROG
RFB2
T
BATTERY PACK
RFB1
4
NTCBIAS
8
FBG
7
Figure 1. Block Diagram of LTC4079
LTC4079 RFB1 hmiww «H |~ I|——I|I}+ 297.5V
LTC4079
9
4079f
For more information www.linear.com/LTC4079
operaTion
The LTC4079 is a full featured constant-current, constant-
voltage charger designed to charge multiple chemistry
types of batteries from voltage sources up to 60V. The low
quiescent current of the device minimizes power drain on
the source and the battery, making it suitable for a variety
of applications including backup and energy harvesting
from an intermittent power source. The battery charge
voltage is set using an external resistor divider. Charge
duration can be set using a capacitor on the TIMER pin.
For safety and improved battery life, the LTC4079 includes
a thermistor input for temperature qualified charging.
Charge current starts when the EN pin is brought above
1.190V. Figure 2 shows a flow chart of the primary states
and state transitions of the LTC4079. A typical charge
cycle includes:
1. Constant-Current (CC) Charging: The programmed
charge current is used to charge the battery until the
battery voltage reaches the charge voltage set using
the feedback divider. For a low ESR battery, this mode
provides the bulk of the charge. The charge timer should
generally be set long enough to charge the battery above
the recharge threshold, otherwise another charge cycle
would immediately follow.
2. Constant-Voltage (CV) Charging: Once the battery
reaches the set charge voltage, constant voltage is
maintained across the battery by controlling the charge
current. The charge current reduces with time in this mode
as the battery nears its full charge capacity.
3. Charging Termination: The LTC4079 can be configured
to terminate charging automatically based on time or
current. The CHRG status pin goes to high impedance
when the charge current reduces below 1/10th of the
programmed current, indicating that the battery is almost
fully charged. The charge current continues to top-off the
battery until the timer terminates the charge current. Timer
termination can be disabled by connecting the TIMER
pin to ground. In this case, charging terminates when
the charge current falls below 1/10th of the programmed
charge current.
A 6ms filter (tTERMINATE) is used on the C/10 detector to
prevent premature termination due to transient loads on
the battery during charging.
4. Automatic Recharge: When VBAT drops below the
recharge threshold (97.6% of the charge voltage),
whether by battery drainage or replacement of the
battery, the charger automatically re-engages and starts
charging.
Setting The Battery Charge Voltage
The battery charge voltage is set by connecting a resistor
divider from the battery to the FB and FBG pins as shown
in Figure 3. The charge voltage is determined as follows:
VCHG =1.170V 1+RFB1
RFB2 +RFBG
where RFB1 is the resistor from BAT to FB, RFB2 is the
resistor from FB to FBG and RFBG is the resistance of the
internal switch of the FBG pin (160Ω typical).
+
BAT
FB
LTC4079 RFB1
RFB2
4079 F03
BATTERY
FBG
ENABLE
Figure 3. Setting the Battery Charge Voltage
Setting and Monitoring the Charge Current
The charge current delivered to the battery in constant-
current mode, ICHG is set using a resistor from the PROG
pin to ground. The value of this resistor is calculated using:
RPROG =
297.5V
ICHG
LTC4079 vEN > u anav vw > z m v N , vW > wmw nu m- WE AWS n n m SAFETY mm EXPIREW 3mm rm? m RANGU EN m mrr REG nnrmmnmm we cv m7 u avw SAFEWHMER Exwguw \m (mm W cv REG mom REG w; m an mzw REG TIMER GROUNDED" VFB < vnenhr.7="" m="" mr-="" w="" ams="" n="" n="" retrv="" mum="" ,="" 57="" ‘io="" l7="" line/“2="" v="" toerch="">
LTC4079
10
4079f
For more information www.linear.com/LTC4079
operaTion
VEN > 0.805V
VIN > 2.57V
VIN – VBAT > 15mV?
ASSERT CHRG STATUS
START SAFELY TIMER IF
TIMER NOT GROUNDED
SHUTDOWN*
BATTERY TEMP
IN RANGE?
EN REG, DIFF REG
OR THERMAL REG
NO CV REG?
VFB < 0.8V?
RUN TIMER
YES
YES
SAFETY TIMER
EXPIRED?
TIMER
GROUNDED?
ICHG < C/10?
IN CV REG, NO EN REG,
DIFF REG OR
THERM REG
1/4 SAFETY TIMER
EXPIRED?
BAD BATTERY*
CHRG REMAINS
ASSERTED
YES
YES
YES
YES
NO
NO
YES
VFB < VRECHG?NO
RETRY COUNT = 5?
YES
NO
NO
NO
NO
YES
NO
NO
NO
YES
PAUSE CHARGE CURRENT
PAUSE TIMER
CHARGING IN EN REG,
DIFF REG OR THERMAL REG
PAUSE TIMER
CC-CV CHARGING
DEASSERT CHRG SATUS
LATCH-OFF*
CHRG REMAINS
ASSERTED
INCREMENT
RETRY
COUNTER
STANDBY
CHARGING TERMINATED
RESET SAFETY TIMER
RESET RETRY COUNTER
DEASSERT CHRG STATUS
SAMPLE FB PIN EVERY 3 SEC
VFB < VRECHG
4079 F02
* VEN < 0.75V OR ULVO TAKES THE DEVICE
TO SHUTDOWN FROM ANY STATE
Figure 2. Battery Charger Operations Flow Chart
250'VPROG L7 LJUW LTC4079 RENI ‘I‘I
LTC4079
11
4079f
For more information www.linear.com/LTC4079
operaTion
Figure 4. Battery Temperature Sensing Using NTC Thermistor
The PROG pin also provides a voltage signal proportional
to the battery charge current. Therefore, the instantaneous
battery current can be determined as follows by monitoring
the PROG pin voltage:
IBAT =
250 V
PROG
RPROG
Minimize the parasitic capacitance while monitoring the
PROG pin voltage as any capacitance on this pin forms a
pole that may cause instability in the charge control loop.
Undervoltage Detection
An internal undervoltage lockout circuit monitors the VIN
voltage and disables the battery charging circuit until VIN
rises above the undervoltage lockout threshold, 2.55V
(typically). The UVLO threshold has built-in hysteresis
of 140mV. Furthermore, the differential UVLO circuit
also keeps the charger in a low quiescent current mode
by disabling the battery charging circuits when VIN falls
below VBAT by more than 65mV. The differential UVLO
has hysteresis of 80mV, with turn-on at VIN-VBAT = 15mV
(typical).
Battery Temperature Qualified Charging
During battery charging, the battery temperature is sensed
by sampling the voltage on the NTC pin every 3 seconds.
Connect a low drift bias resistor from the NTCBIAS output
to the NTC input and a negative temperature coefficient
(NTC) thermistor, close to the battery pack, from the NTC
pin to ground, as shown in Figure 4. The bias resistor should
be equal to the value of the chosen thermistor at 25°C.
The LTC4079 pauses charging and the charge timer when
the NTC pin voltage indicates that the thermistor resistance
has dropped to 0.576 times its room temperature value.
For a Vishay curve 2 thermistor, this corresponds to 40°C.
Charging is also paused when the thermistor resistance
increases to 2.816 times the room temperature value. For
a Vishay curve 2 thermistor, this increase corresponds
to 0°C.
The hot and cold trip points can be adjusted using a
different type of thermistor, or a different RBIAS resistor,
or by adding a desensitizing resistor in series with the
thermistor, or by a combination of these measures.
Charging resumes when the battery temperature returns to
the normal range and the timer continues from the point
where it was paused.
Input Voltage Regulation
The LTC4079 can regulate a constant voltage on the IN pin
when charging from a current-limited power source such
as a weak battery or a solar panel. This feature can be used
to prevent the input voltage from collapsing below UVLO,
or to maintain the input source voltage at peak power.
The charge current is reduced as the input voltage falls to
the threshold set by an external resistor divider from the
input power source to the EN pin and GND, as shown in
Figure 5. The input voltage regulation threshold, VIN(REG)
is calculated as follows:
VIN(REG) =1.190V 1+REN1
REN2
This regulation mechanism allows the charge current to be
selected based on battery requirement and the maximum
power available from the charging source. The LTC4079
automatically reduces the charge current when the input
source cannot provide the programmed charge current.
When input voltage regulation is not needed, connect the
EN pin to the input power source or a digital enable signal.
+
TOO COLD
INTERNAL SUPPLY
NTC SAMPLE
PULSE
NTC RBIAS
RNTC
4079 F04
T
NTCBIAS
BAT
LTC4079
73.8% VNTCBIAS
36.6% VNTCBIAS
+
TOO HOT
0.1V
+
IGNORE NTC
+
LTc4079
LTC4079
12
4079f
For more information www.linear.com/LTC4079
operaTion
IN
INPUT POWER
SOURCE REN1
REN2
EN
4079 F05
LTC4079
Figure 5. Setting Input Voltage Regulation
Differential Voltage (VIN-VBAT) Regulation
The LTC4079 provides an additional method to keep the
input voltage from collapsing when the input power comes
from a weak power source. If the input voltage falls close
to the battery voltage, the differential voltage regulation
loop in LTC4079 keeps the input voltage above the battery
voltage by 160mV (typical value) by reducing the charge
current as the input to battery differential voltage falls.
In both of the above regulation conditions, the input source
must provide at least the quiescent current of the device to
prevent UVLO. The charge timer is paused whenever the
charge current is reduced due to input voltage regulation
or differential voltage regulation.
Thermal Regulation
An internal thermal feedback loop reduces the charge
current below the programmed value if the die temperature
approaches 118°C. This feature protects the LTC4079
from excessive temperature and allows the user to set
the charge current to typical (not worst case) ambient
temperature with the assurance that the charger will
automatically reduce the current to prevent overheating
in worst-case conditions.
The charge timer is paused during thermal limiting to
prevent under-charging the battery and to allow the full
charge current to flow for the set timer duration.
C/10 Termination
The LTC4079 supports a current based termination scheme,
where a battery charge cycle terminates when the current
output from the charger falls below one-tenth of the
programmed charge current. The C/10 threshold current
corresponds to 119mV on the PROG pin. This termination
mode is engaged by shorting the TIMER pin to ground.
When C/10 termination is used, the LTC4079 provides
battery charge current as long as the current remains
above the C/10 threshold. As the battery terminal voltage
reaches the target charge voltage, the charge current falls
until the C/10 threshold is reached, at which time the
charger terminates and the LTC4079 enters standby mode.
Premature termination is prevented when input voltage,
differential or thermal regulation is active.
To prevent termination-recharge oscillations, it is important
to set the termination charge current low enough for bat-
teries with high internal resistance. For a nominal recharge
threshold of 2.4% below the charge voltage, the charge
current should be set as follows with sufficient margin:
ICHG <0.24VCHG
RBAT
where RBAT is the battery's internal series resistance. The
CHRG status pin is high impedance when the charger is
not actively charging.
Timer Termination
The LTC4079 also supports a timer-based termination
scheme, where the battery charge cycle is terminated after
a specific amount of time elapses. Connect a capacitor
from the TIMER pin to ground to engage timer based
charge termination. Calculate the capacitance required
for the desired charge cycle duration, tTIMER as follows:
CTIMER = tTIMER • 18.2nF/Hr
A 200nA current source is used to source/sink current
to/from CTIMER to generate a sawtooth periodic signal
(nominally 0.8V to 1.2V) for use by the timer. Since the
TIMER pin current is small, minimize leakage on this pin
to maintain timer accuracy.
The timer starts on charger enable or the beginning of a
recharge cycle, and is reset on disable or when VIN falls
below UVLO or DUVLO.
The timer is paused whenever the charge current is limited
by EN pin or differential voltage or thermal regulation,
unless the charger is also in constant-voltage regulation
mode. It is also paused with the charge current during an
NTC fault. The timer is not paused if the charge current is
LTC4079 L7HEJWEGR 1 3
LTC4079
13
4079f
For more information www.linear.com/LTC4079
operaTion
limited by dropout. For example, for a programmed charge
current of 100mA, this occurs when VIN-VBAT falls below
about 0.5V due to the voltage drop across the charge path
(5Ω typically). If VIN-VBAT falls below 160mV to trigger
differential voltage regulation, the timer will be paused.
The CHRG status pin signals charging at a rate of more
than C/10, regardless of which termination scheme is
used. When timer termination is used, the CHRG status
pin pulls low during a charging cycle until the charger
output current falls below the C/10 threshold. The charger
continues to top off the battery until timer termination,
when the LTC4079 enters standby mode.
Standby and Automatic Recharge
If the LTC4079 remains enabled after charge cycle
termination, it monitors the battery voltage in standby
mode by sampling the FB pin connected to the external
resistor divider. In order to minimize the battery drain, the
feedback divider is only turned on (by connecting FBG pin
to ground) for 210µs once every 3 seconds. When this
sampling detects that the battery voltage has dropped
by more than 2.4%, the feedback divider is kept on for
1.5 seconds (typical). If the FB voltage remains below
the recharge threshold for more than 2.5ms (typical), a
recharge cycle starts. This 2.5ms filter prevents premature
recharge due to load transients. The recharge cycle also
terminates in constant-voltage charge mode as described
above. The automatic recharge function maintains that the
battery at, or near, a fully charged condition.
If the battery voltage remains below the recharge threshold
on timer expiration, another recharge cycle begins as
explained below.
Timer Retry and Latch-off
A new charge cycle is started if the battery voltage remains
below the recharge threshold at the end of a charge cycle.
This happens in the following situations: 1) the timer is
not set long enough for the battery with the programmed
charge current, 2) the battery is defective, 3) a load drains
the battery during charging, 4) charge current is limited
by dropout.
In order to avoid wasting power in recharging a defective
battery indefinitely, LTC4079 contains a recharge latch-
off feature. Charging is latched off and the CHRG pin
remains asserted after 5 recharge attempts if the battery
voltage remains below the recharge threshold at the end
of all five recharge cycles. The latch-off counter is reset
if a charge cycle terminates normally during any recharge
attempt, or if the charge current falls below ICHG/10 in
constant-voltage regulation mode during a charge cycle.
Charger disable using the EN pin or UVLO also resets the
latch-off counter..
Bad Battery Scenario
If the feedback voltage remains below VFB(LOWBAT) for
longer than 1/4th of the safety timer set by CTIMER, the
battery is considered bad. Charging stops in this case and
the CHRG pin remains asserted. NTC sampling and FB
sampling for recharge is also turned-off. The charge cycle
is restarted by toggling the EN pin below VEN(SD) (typically
0.75V) and then back high. UVLO also clears the bad battery
lockout. There is no bad battery detection when the battery
charge timer is disabled (TIMER pin grounded).
CHRG Status Output
The charge status open-drain output (CHRG) has two
states: pull down and high impedance. The pull-down
state indicates that LTC4079 is in charging mode. A high
impedance state indicates that the charge current has
dropped below 10% of the programmed charge current. In
most cases, charge current is reduced due to the constant-
voltage loop, meaning that the battery voltage is near the
target charge voltage. But if charge current is reduced due
to VIN regulation (through EN or VIN-VBAT regulation) or
thermal regulation, CHRG remains asserted until only the
constant-voltage regulation loop reduces charge current
below 10% of the programmed charge current.
A high impedance state at the CHRG pin occurs on timer
termination, or UVLO or differential UVLO, or when the
LTC4079 is disabled by pulling EN low. This output can
be used as a logic interface or to light a low power LED.
LTC4079 RFB1 K1 14 |+ III—4h
LTC4079
14
4079f
For more information www.linear.com/LTC4079
applicaTions inForMaTion
Feedback Divider Selection
Using too low or too high values of resistors for the
feedback divider can cause small charge voltage errors
due to: 1) Finite on-resistance of the internal switch on
the FBG pin and 2) leakage on the FB pin. The impact of
these two factors on the target battery charge voltage is
calculated as follows:
VCHG =1.170V 1+RFB1
RFB2 +RFBG
+RFB1 (IFB +ILEAK
)
where RFB1 and RFB2 are the top and bottom resistors of
the feedback divider, RFBG is the resistance of the internal
switch from the FBG pin to GND (160Ω typical) and ILEAK
is the parasitic leakage on the FB pin as shown in Figure
6. A graph of IFB vs Temperature is given in the Typical
Performance section.
According to the above equation, high value feedback
resistors minimize the impact of RFBG, while low values
minimize the impact of IFB and lLEAK. A Thevenin equivalent
resistance of 100k to 500k on the FB node is generally a
good compromise in most scenarios.
Table 1. Recommended 1% Resistors for Common Battery
Charge Voltages
VCHG RFB1 RFB2 TYPICAL ERROR
3.6V 1070k 511k +0.53%
4.1V 422k 169k –0.27%
4.2V 1070k 412k +0.18%
7.2V 1370k 267k –0.42%
8.2V 1070k 178k -0.04%
8.4V 1540k 249k +0.02%
12.3V 1780k 187k -0.02%
12.6V 2550k 261k -0.05%
Stability Considerations
When the charger is in constant-current mode, the PROG
pin impedance forms part of the charger current control
loop. The constant-current mode stability is therefore
affected by the roll-off frequency of the PROG pin
impedance. With minimum capacitance on this pin (less
than about 10pF), the charger is stable with a program
resistor, RPROG, as high as 60k (ICHG = 5mA); however,
any additional capacitance at this pin limits the maximum
allowed program resistor.
The constant-voltage loop is stable without any
compensation as long as a typical low impedance battery
is connected to the BAT pin. However, aF capacitor with
series resistor is recommended when charging high
ESR batteries, typically more than 1kΩ.
Charging High Resistance Batteries
When charging a battery with high internal resistance,
the battery voltage can rise quickly, entering constant-
voltage mode. If the charge current falls below 1/10th of
the programmed charge current, charging may terminate
based on C/10 even if a timer capacitor is connected
on the TIMER pin. This is because C/10 termination is
assumed if the timer pin remains below 0.3V. With only
200nA being sourced from the TIMER pin, a large timer
capacitance may limit the TIMER voltage below 0.3V for
a short duration at the beginning of a charge cycle. After
charging terminates, a recharge cycle would begin if the
+
BAT
FB
LTC4079
PARASITIC
LOAD
RFB1
RFB2 ILEAK
4079 F06
BATTERY
FBG
ENABLE
IFB
Figure 6. Feedback Divider Considerations
For example, for RFB1 = 1.54M and RFB2 = 249k (for bat-
tery charge voltage of 8.4V), accounting for RFBG =160Ω
lowers the charge voltage by 0.06%, while ILEAK = 10nA
raises it by 0.18%.
Table 1 lists possible choices of standard 1% resistor
values for common battery charge voltages. The Typical
Error column gives systematic error due to the granularity
in the values of 1% resistors.
LTC4079 118004A L7HEJWEGR 1 5
LTC4079
15
4079f
For more information www.linear.com/LTC4079
applicaTions inForMaTion
internal battery voltage has not been charged above the
recharge threshold, determined by VRECHRG and the
feedback divider. As shown in Figure 7, this charge/recharge
cycle continues until the TIMER pin rises above 0.3V, at
which point timer termination is engaged and the battery
is charged for the duration set by the timer capacitor.
Example: Consider an LTC4079 operating from a 12V
input source programmed to supply 100mA current to
a discharged 2-cell Li-Ion battery with a voltage of 6.6V.
Assuming θJA is 43°C/W the ambient temperature at which
the charge current begins to fall due to thermal regulation is:
TA = 118°C – (12V-6.6V) • 100mA • 43°C/W = 95°C
The LTC4079 can be used above 95°C ambient but the
charge current will be reduce linearly from the programmed
value of 100mA to 0mA as the ambient temperature
increases from 95°C to 118°C.
Increasing Thermal Regulation Current
In applications with large VIN to VBAT drop, the charge
current can be significantly reduced during thermal regula-
tion. One way to increase the thermally regulated charge
current is to dissipate some of the power in a resistor in
series with the IN pin. This works well when the resistor
value is designed to be small enough to avoid pushing the
LTC4079 into dropout.
Input Capacitor Selection
When an input supply is connected to a portable product,
the inductance of the cable and the high Q ceramic input
capacitor form an L-C resonant circuit. While the LTC4079
is capable of withstanding input voltages as high as 62V, if
the input cable does not have adequate mutual inductance
or if there is not much impedance in the cable, it is possible
for the voltage at the input of LTC4079 to reach as high as
2x the cable input voltage before it settles out. To prevent
excessive voltage from damaging the LTC4079 during a
hot insertion, it is best to have a low voltage coefficient
capacitor at the supply input pin of the LTC4079.
Using a tantalum capacitor or an aluminum electrolytic
capacitor for input bypassing, or paralleling with a ce-
ramic capacitor will also reduce voltage overshoot during
a hot insertion.
Power Dissipation and Thermal Regulation
The LTC4079 automatically reduces charge current
during high power conditions that result in high junction
temperature. Therefore, it is not necessary to design
the charging system for worst-case power dissipation
scenarios. The conditions that cause the LTC4079 to
reduce charge current through thermal regulation can be
approximated by considering the power dissipated in the
IC. Most of the power dissipation is in the charge path.
Thus the power dissipation is approximately:
PD = (VIN-VBAT) • IBAT
The approximate ambient temperature at which the thermal
regulation begins to lower the charge current is:
TA = 118°C – PDθJA
TA = 118°C – (VIN-VBAT) • IBATθJA
The reduced charge current at an ambient temperature
above the onset of thermal regulation can be calculated
as follows:
IBAT =
118°C T
A
VIN – VBAT
( )
θJA
Figure 7. Repeated Charge Terminations on
Startup Due to High Resistance of the Battery,
CTIMER=82nF, VCHG=4.2V, ICHG=10mA and
Battery Resistance=300Ω
VBAT
0.2V/DIV
TIMER
0.5V/DIV
PROG
0.1V/DIV
CHRG
5V/DIV
20ms/DIV 4079 F01
4.2V
LTc4079
LTC4079
16
4079f
For more information www.linear.com/LTC4079
Board Layout Considerations
When laying out the printed circuit board, the following
checklist should be followed to ensure proper operation
of the LTC4079:
1. Connect the exposed pad of the package (Pin 11)
directly to a large PC board ground to minimize thermal
impedance. Correctly soldered to a 1500mm2 double
sided 1oz copper board, the LTC4079 DFN package has
a thermal resistance (θJA) of approximately 43°C/W.
Failure to make good contact between the exposed pad
on the backside of the package and an adequately sized
ground plane results in much larger thermal resistance.
2. The top of the feedback divider resistor should be
connected as close to the positive battery terminal as
possible in order to avoid inaccuracies due to voltage
drop in the charge current path. The negative terminal
of the battery should be connected to the chip ground
plane directly to avoid any ground loop induced charge
voltage inaccuracy.
applicaTions inForMaTion
3. Minimize the parasitic capacitance and leakage on the
FB node for stability and charge voltage accuracy.
4. Minimize the parasitic capacitance and leakage on the
TIMER pin for timer accuracy.
5. Minimize the parasitic capacitance on the PROG pin for
stable operation.
6. Minimize the parasitic capacitance and leakage on the
EN pin if it is connected to a resistor divider from the
input supply for input voltage regulation.
LTC4079 L7 LJUW
LTC4079
17
4079f
For more information www.linear.com/LTC4079
Typical applicaTions
Li-Ion Charger with Timer Termination
In the Figure 8 configuration, the input source charges
the battery for 5½ hours and also supplies current to the
load. The maximum current provided by the charger (on
BAT pin) is limited to the charge current of 246mA set by
the 1.21k resistor on the PROG pin. A small resistor is
used in series with the input supply to reduce VIN-VBAT,
and thereby increase the available charge current during
thermal regulation. Once the battery is charged, it sup-
plies power to the load until VBAT falls below the recharge
threshold, at which point a recharge cycle starts.
Figure 8. Li-Ion Charger with Timer Termination
BAT
FB
FBG
EN
NTCBIASPROG
NTC
GND
LTC4079
TIMER
1.54M
1.21k
25Ω, 2W
100nF
F
TO
LOAD
249k
10k
4079 F08
BATTERY
PACK
VCHG = 8.4V
ICHG = 246mA
CHRG
IN
24V
SUPPLY
+
T
10k
2-Cell NiMH Trickle Charger from Automotive Supply
with Timer Termination
Figure 9 shows a trickle charger for 2-cell, 2500mAh,
AA NiMH battery with timer termination after 31 hours.
Charge current drops when the battery voltage reaches
1.65V per cell.
Figure 9. NiMH Trickle Charger with Timer Termination
BAT
FB
FBG
EN
NTCBIASPROG
NTC
GND
LTC4079
TIMER
324k
3.01k
560nF
F
TO
LOAD
178k
4079 F09
2500mAh
2-CELL
NiMH
VCHG = 3.3V
ICHG = 99mA
CHRG
IN
12V
CAR BATTERY
+
Li-Ion Charging from a Solar Panel with Differential
Voltage Regulation, C/10 Termination
Figure 10 shows a simple charging solution from a solar
panel. Differential voltage regulation reduces charge current
to prevent the panel voltage from drooping below the
battery voltage when charging under low light conditions.
The LTC4079 does not require a Schottky diode in series
with the panel.
Supercapacitor Charger from 2-Cell Li-ion
Charging terminates when the stacked supercapacitor
voltage reaches the set charge voltage. A recharge cycle
begins automatically when the supercap voltage falls
below the recharge threshold. A resistor divider balancer
can optionally be switched in for balancing a stacked
supercapacitor during charging.
Figure 10. Li-Ion Charger with Differential Voltage Regulation
BAT
FB
FBG
EN
NTCBIASPROG
NTC
GND
LTC4079
TIMER
1.54M
1.21k
FF
TO
LOAD
249k
10k
4079 F10
BATTERY
PACK
VCHG = 8.4V
ICHG = 246mA
CHRG
IN
+
SOLAR
PANEL
+
T
10k
Figure 11. Supercap Charger with C/10 Termination
BAT
2-CELL
Li-Ion
FB
FBG
EN
NTCBIASPROG
NTC
GND
LTC4079
TIMER
1.02M
30.1k
CSC
0.6F
HS206
TO
LOAD
309k
1k
1k
SUPERCAP BALANCER (OPTIONAL)
FDG6308P
4079 F11
VCHG = 5.0V
ICHG = 10mA
CHRG
IN
+
LTC4079 18
LTC4079
18
4079f
For more information www.linear.com/LTC4079
Typical applicaTions
12V Lead-Acid Charger from Rectified 24V AC
In the following charging circuit example, a lead acid
battery is trickle charged at a C/10 rate for 15 hours. An
NTC thermistor is used to alter the target charge voltage
of the lead-acid battery based on the battery temperature.
Figure 12. Lead-Acid Battery Trickle Charger from Rectified 24V AC
BAT
FB
FBG
EN
NTCBIASPROG
NTC
GND
LTC4079
TIMER
1M
3.01k
24V AC
F
TO
LOAD
100µF
12V
LEAD-ACID
BATTERY
100k
102k
270nF
T
4079 F12
CHRG
IN
+
100k
ICHG = 99mA
LTC4079 L7HEJWEGR 1 9
LTC4079
19
4079f
For more information www.linear.com/LTC4079
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
package DescripTion
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
3.00 ±0.10
(4 SIDES)
NOTE:
1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2).
CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE
TOP AND BOTTOM OF PACKAGE
0.40 ± 0.10
BOTTOM VIEW—EXPOSED PAD
1.65 ± 0.10
(2 SIDES)
0.75 ±0.05
R = 0.125
TYP
2.38 ±0.10
(2 SIDES)
15
106
PIN 1
TOP MARK
(SEE NOTE 6)
0.200 REF
0.00 – 0.05
(DD) DFN REV C 0310
0.25 ± 0.05
2.38 ±0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
1.65 ±0.05
(2 SIDES)2.15 ±0.05
0.50
BSC
0.70 ±0.05
3.55 ±0.05
PACKAGE
OUTLINE
0.25 ± 0.05
0.50 BSC
DD Package
10-Lead Plastic DFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1699 Rev C)
PIN 1 NOTCH
R = 0.20 OR
0.35 × 45°
CHAMFER
LTC4079 1‘? $1. m zzuH awn 20
LTC4079
20
4079f
For more information www.linear.com/LTC4079
LINEAR TECHNOLOGY CORPORATION 2014
LT 0914 • PRINTED IN USA
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 FAX: (408) 434-0507 www.linear.com/LTC4079
relaTeD parTs
Typical applicaTion
Energy Harvesting Charger with Buck, Buck-Boost and LDO Supplies
BAT
FB
FBG
EN
NTCBIASPROG
NTC
GND
LTC4079
TIMER
1.07M1.2M
VIN(REG) = 15V
ICHG = 99mA
102k
3.01k
100nF
412k
10k
TLi-Ion
CHRG
IN
PIEZO
MIDE
V25W
F
6.3V
4.7µF
6.3V
GND
LTC3330
4079 TA02
AC1
VIN
CAP
VIN2
BAT
OUT[2:0]
LDO[2:0]
IPK[2:0]
UV[3:0]*
AC2
SW
SWA
22µH
22µH
SWB
VOUT
LDO_IN
SCAP
BAL
LDO_EN
EH_ON
PGVOUT
PGLDO
LDO_OUT
VIN3
3V TO 19V
4V TO 19V
SOLAR
PANEL
10µF
25V
3
3
3
4
F
6.3V
22µF
6.3V
4.7µF
1.2V TO 3.6V
50mA
1.8V TO 5V
50mA
10mF
2.7V
10mF
2.7V
OPTIONAL
47µF
6.3V
+
+
SET VIN(REG) OF LTC4079 ABOVE THE UVLO THRESHOLDS OF LTC3330.
E.G. VIN(REG) = 15V FOR UVLO RISING = 14V AND UVLO FALLING = 13V.
THIS ENSURES THAT THE BATTERY IS CHARGED ONLY WHEN EXCESS
POWER IS AVAILABLE FROM THE INPUT SOURCE.
*
10k
PART NUMBER DESCRIPTION COMMENTS
LTC4078 Dual Input Li-Ion Battery Charger with Overvoltage
Protection
Overvoltage Protection Up to 22V. Charge Current 100mA to 950mA.
LTC4065/LTC4065A 250mA Li-Ion Battery Charger 3.75V to 5.5V Input. Up to 250mA Programmable Charge Current. Internal
4.5Hrs Safety Timer.
LTC4054L-4.2 150mA Linear Li-Ion Battery Charger 4.25V to 6.5V Input. 10mA to 150mA Programmable Charge Current.
LTC4070 Li-Ion/Polymer Shunt Battery Charger IQ = 0.5µA, Pin Selectable Battery Charge Voltage: 4.0V, 4.1V or 4.2V
LTC4071 Li-Ion/Polymer Shunt Battery Charger with Low Battery
Disconnect
Pack Protection Version of LTC4070
LT
®
3650 High Voltage 2A Monolithic Li-Ion Battery Charger 4.75V to 32V Input. Buck Architecture.
LTC4121/
LTC4121-4.2
High Voltage 400mA Synchronous Step-Down Battery
Charger
4.4V to 40V Input. Low Dropout Buck Architecture with MPPT.

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