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Final Electrical Specifications
LTC1731-4.1 Lithium-Ion Linear Battery Charger Controller
April 2000
FEATURES
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DESCRIPTION
The LTC (R)1731-4.1 is a complete constant-current/constant-voltage linear charge controller for lithium-ion batteries. Nickel-cadmium (NiCd) and nickel-metal-hydride (NiMH) batteries can also be charged with constant current using external termination. The external sense resistor sets the charge current with 5% accuracy. An internal resistor divider and precision reference set the final float potential with 1% accuracy. The output float voltage is set internally to 4.1V. When the input supply is removed, the LTC1731 automatically enters a low current sleep mode, dropping the battery drain current to 7A typically. An internal comparator detects the end-of-charge (C/10) condition while a programmable timer, using an external capacitor, sets the total charge time. Fully discharged cells are automatically trickle charged at 10% of the programmed current until cell voltage exceeds 2.457V. The LTC1731-4.1 is available in the 8-pin MSOP and SO packages.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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Complete Linear Charger Controller for 1-Cell Lithium-Ion Batteries 1% Voltage Accuracy Programmable Charge Current C/10 Charge Current Detection Output Programmable Charge Termination Timer Space Saving, Thin 8-Pin MSOP Package Automatic Sleep Mode When Input Supply is Removed (7A Battery Drain) Automatic Trickle Charging of Low Voltage Cells Programmable for Constant-Current-Only Mode
APPLICATIONS
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Cellular Phones Handheld Computers Charging Docks and Cradles Programmable Current Source
TYPICAL APPLICATION
500mA Li-Ion Charger
VIN 5V TO 12V MBRM120T3 7 1k CHARGE STATUS VCC SENSE 2 CHRG DRV 8 6 RSENSE 0.2 Q1 Si9430DY IBAT = 500mA
LTC1731-4.1 3 CTIMER 0.1F TIMER BAT PROG GND 4 1 5 RPROG* 19.6k
+ Li-ION
CELL
1731 TA01
*SHUTDOWN INVOKED BY FLOATING THE PROG PIN
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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
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1F
10F
1
LTC1731-4.1
ABSOLUTE MAXIMUM RATINGS
Input Supply Voltage (VCC) ................................... 13.2V Input Voltage (SENSE, DRV, BAT, TIMER, PROG) ....................... - 0.3V to (VCC + 0.3V) Output Voltage (CHRG) ......................... - 0.3V to 13.2V
PACKAGE/ORDER INFORMATION
TOP VIEW BAT CHRG TIMER GND 1 2 3 4 8 7 6 5 SENSE VCC DRV PROG
ORDER PART NUMBER
BAT 1
LTC1731EMS8-4.1 MS8 PART MARKING LTJK
MS8 PACKAGE 8-LEAD PLASTIC MSOP
TJMAX = 150C, JA = 180C/W
Consult factory for Industrial and Military grade parts.
The q denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 6V unless otherwise noted.
SYMBOL VCC ICC PARAMETER Input Supply Voltage Input Supply Current Charger On, Current Mode Shutdown Mode Sleep Mode (Battery Drain Current) (5V VCC 12V) RPROG = 19.6k, RSENSE = 0.2 RPROG = 19.6k, RSENSE = 0.2 RPROG = 97.6k, RSENSE = 0.2 VBAT = 2V, RPROG = 19.6k, ITRIKL = (VCC - VSENSE)/0.2 From Low to High From Low to High PROG Pin Low to High PROG Pin High to Low CONDITIONS
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ELECTRICAL CHARACTERISTICS
VBAT IBAT
Regulated Output Voltage Current Mode Charge Current
ITRIKL VTRIKL VUV VUV VMSD
Trickle Charge Current Trickle Charge Threshold Voltage VCC Undervoltage Lockout Voltage VCC Undervoltage Lockout Hysteresis Manual Shutdown Threshold Voltage
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(Note 1)
Operating Temperature Range (Note 2) .....- 40 to 85C Storage Temperature Range ................. - 65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C
TOP VIEW 8 7 6 5 SENSE VCC DRV PROG
ORDER PART NUMBER LTC1731ES8-4.1 S8 PART MARKING 173141
CHRG 2 TIMER 3 GND 4
S8 PACKAGE 8-LEAD PLASTIC SO
TJMAX = 150C, JA = 125C/W
MIN 4.5
TYP 1 1 7
MAX 12 3 2 20 4.141 535 585 130 100 2.55 4.5
UNITS V mA mA A V mA mA mA mA V V mV V V
4.059 465 415 70 30 2.35
4.1 500 100 50 2.457 4.1 200 2.457 2.446
LTC1731-4.1
The q denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 6V unless otherwise noted.
SYMBOL VASD VDIS IPROG VPROG ICHRG VCHRG IC/10 tTIMER VCLAMP PARAMETER Automatic Shutdown Threshold Voltage Voltage Mode Disable Threshold Voltage PROG Pin Current PROG Pin Load Regulation PROG Pin Voltage CHRG Pin Weak Pull-Down Current CHRG Pin Output Low Voltage End of Charge Indication Current Level TIMER Accuracy DRV Pin Clamp Voltage CONDITIONS (VCC - VBAT) High to Low (VCC - VBAT) Low to High VTIMER Internal Pull-Up Current, No RPROG PROG Pin Source Current, VPROG 5mV RPROG =19.6k VCHRG = 1V ICHRG = 5mA RPROG = 19.6k, RSENSE = 0.2 CTIMER = 0.1F VCLAMP = VCC - VDRV, IDRIVE = 50A
q q q
ELECTRICAL CHARACTERISTICS
MIN 30 40 5.6
TYP 54 69 2.5
MAX 90 100
UNITS mV mV V A A V
300 2.457 50 25 100 0.6 50 10 6.5 150 1.2 100
A V mA % V
Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired.
Note 2: The LTC1731-4.1 is guaranteed to meet performance specifications from 0C to 70C. Specifications over the - 40C to 85C operating temperature range are assured by design, characterization and correlation with statistical process controls. Guaranteed I grade parts are available, consult factory.
PIN FUNCTIONS
BAT (Pin 1): Battery Sense Input. A bypass capacitor of at least 10F is required to keep the loop stable when the battery is not connected. A precision internal resistor divider sets the final float potential on this pin. The resistor divider is disconnected in sleep mode. CHRG (Pin 2): Open-Drain Charge Status Output. When the battery is being charged, the CHRG pin is pulled low by an internal N-channel MOSFET. When the charge current drops to 10% of the full-scale current for at least 0.32 seconds, the N-channel MOSFET turns off and a 100A current source is connected from the CHRG pin to GND. When the timer runs out or the input supply is removed, the current source will be disconnected and the CHRG pin is forced into a high impedance state. TIMER (Pin 3): Timer Capacitor and Constant-Voltage Mode Disable Input Pin. The timer period is set by placing a capacitor, CTIMER, to GND. The timer period is tTIMER = (CTIMER * 3 hours)/(0.1F). When the TIMER pin is connected to VCC, the constant-voltage mode is disabled and the charger will operate in constant-current mode only. Short the TIMER pin to GND to disable the internal timer function. GND (Pin 4): Ground. PROG (Pin 5): Charge Current Program and Shutdown Input Pin. The charge current is programmed by connecting a resistor, RPROG to ground. The charge current is IBAT = (VPROG * 800)/(RPROG * RSENSE). The IC can be forced into shutdown by floating the PROG pin and allowing the internal 2.5A current source to pull the pin above the 2.457V shutdown threshold voltage. DRV (Pin 6): Drive Output Pin for the P-Channel MOSFET or PNP Transistor. The impedance is high at this pin, therefore, a high gain PNP pass transistor should be used. The DRV pin is internally clamped to 6.5V below VCC. VCC (Pin 7): Positive Input Supply Voltage. When VBAT is within 54mV of VCC, the LTC1731 is forced into sleep mode, dropping ICC to 7A. VCC ranges from 4.5V to 12V (LTC1731-4.1). Bypass this pin with a 1F capacitor. SENSE (Pin 8): Current Sense Input. A sense resistor, RSENSE, must be connected from VCC to the SENSE pin. This resistor is chosen using the following equation: RSENSE = (VPROG * 800)/(RPROG * IBAT)
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LTC1731-4.1
BLOCK DIAGRA
2
CHRG
C/10 STOP C/10 100A SHDN LOGIC SLP
720
3
OSCILLATOR VREF
COUNTER
+
C3
+
A1
-
-
2.5A VREF 2.457V CHARGE PROG RPROG GND
5 BATTERY CURRENT IBAT = (2.457V * 800)/(RPROG * RSENSE)
OPERATIO
The LTC1731 is a linear battery charger controller. The charge current is programmed by the combination of a program resistor (RPROG) from the PROG pin to ground and a sense resistor (RSENSE) between the VCC and SENSE pins. RPROG sets a program current through an internal trimmed 800 resistor setting up a voltage drop from VCC to the input of the current amplifier (CA). The current amplifier servos the gate of the external P-channel MOSFET to force the same voltage drop across RSENSE which sets the charge current. When the potential at the BAT pin approaches the preset float voltage, the voltage amplifier (VA) will start sinking current which reduces the voltage drop across RSENSE, thus reducing the charge current.
Charging begins when the potential at VCC pin rises above the UVLO level and a program resistor is connected from the PROG pin to ground. At the beginning of the charge cycle, if the cell voltage is below 2.457V, the charger goes into trickle charge mode. The trickle charge current is 10% of the full-scale current. If the cell voltage stays low for one quarter of the total charge time, the charge sequence will be terminated immediately. The charger goes into the fast charge constant-current mode after the voltage on the BAT pin rises above 2.457V. In constant-current mode, the charge current is set by the combination of RSENSE and RPROG.
4
+
VCC
VA
-
+
TIMER
LBO
C2
-
+
-
W
VCC 7 RSENSE
+
C1 80 800
SENSE
8
-
C4
+ - + -
CA
54mV
DRV BAT
6 1
4
1731 BD
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LTC1731-4.1
OPERATIO
When the battery approaches the final float voltage, the charge current will begin to decrease. When the current drops to 10% of the full-scale charge current, an internal comparator will turn off the pull-down N-channel MOSFET at the CHRG pin and connect a weak current source to ground to indicate an end-of-charge (C/10) condition. An external capacitor on the TIMER pin sets the total charge time. After a time-out occurs, the charging will be terminated immediately and the CHRG pin is forced to a high impedance state. To restart the charge cycle, simply remove the input voltage and reapply it, or float the PROG pin momentarily.
APPLICATIONS INFORMATION
Charge Termination The charger is off when any of the following conditions exist: the voltage at the VCC pin is below 4.1V, the voltage at the VCC pin is higher than 4.1V but is less than 54mV above VBAT, or the PROG pin is floating. The DRV pin will be pulled to VCC and the internal resistor divider is disconnected to reduce the current drain on the battery. Undervoltage Lockout (UVLO) An internal undervoltage lockout circuit monitors the input voltage and keeps the charger in shutdown mode until VCC rises above 4.1V. To prevent oscillation around VCC = 4.1V, the UVLO circuit has built-in hysteresis. Trickle Charge and Defective Battery Detection At the beginning of the charging sequence, if the battery voltage is low (below 2.457V) the charger goes into trickle mode. The charge current is dropped to 10% of the fullscale current. If the low cell voltage persists for one quarter of the total charging time, the battery is considered defective, the charging will be terminated and the CHRG pin output is forced to a high impedance state. Shutdown The LTC1731 can be forced into shutdown by floating the PROG pin thus allowing the internal 2.5A current source to pull the pin above the 2.457V shutdown threshold voltage. The DRV pin will then be pulled up to VCC and turn off the external P-channel MOSFET. The internal timer is reset in the shutdown mode. Programming Charge Current The formula for the battery charge current (see Block Diagram) is: IBAT = (IPROG)(800/RSENSE) = (2.457V/RPROG)(800/RSENSE) where RPROG is the total resistance from the PROG pin to ground. For example, if 0.5A charge current is needed, select a value for RSENSE that will drop 100mV at the maximum charge current. RSENSE = 0.1V/0.5A = 0.2, then calculate: RPROG = (2.457V/500mA)(800/0.2) = 19.656k For best stability over temperature and time, 1% resistors are recommended. The closest 1% resistor value is 19.6k.
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For batteries like lithium-ion that require accurate final float potential, the internal 2.457V reference, voltage amplifier and the resistor divider provide regulation with 1% (max) accuracy. For NiMH and NiCd batteries, the LTC1731 can be turned into a current source by pulling the TIMER pin to VCC. When in the constant-current only mode, the voltage amplifier, timer and the trickle charge function are all disabled. When the input voltage is not present, the charger goes into a sleep mode, dropping ICC to 7A. This greatly reduces the current drain on the battery and increases the standby time. The charger can be shut down by floating the PROG pin. An internal current source will pull it high and clamp at 3.5V.
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LTC1731-4.1
APPLICATIONS INFORMATION
Programming the Timer The programmable timer is used to terminate the charge. The length of the timer is programmed by an external capacitor at the TIMER pin. The total charge time is: Time = (3 Hours)(CTIMER/0.1F) The timer starts when the input voltage greater than 4.1V is applied and the program resistor is connected to ground. After a time-out occurs, the CHRG output will turn into a high impedance state to indicate that the charging has stopped. Connecting the TIMER pin to VCC disables the timer and also puts the charger into a constant-current mode. To only disable the timer function, short the TIMER pin to GND. CHRG Status Output Pin When the charge cycle starts, the CHRG pin is pulled down to ground by an internal N-channel MOSFET that can drive an LED. When the charge current drops to 10% of the fullscale current (C/10), the N-channel MOSFET is turned off and a weak 100A current source to ground is connected to the CHRG pin. After a time-out occurs, the pin will go into a high impedance state. By using two different value pull-up resistors, a microprocessor can detect three states from this pin (charging, C/10 and stop charging). See Figure 1.
V+ 7 VCC LTC1731-4.1 CHRG 2 100k 1k OUT IN
1731 F01
VDD
PROCESSOR
Figure 1. Microprocessor Interface
When the LTC1731 is in charge mode, the CHRG pin is pulled down by an internal N-channel MOSFET. To detect this mode, force the digital output pin, OUT, high and measure the voltage at the CHRG pin. The N-channel MOSFET will pull the pin low even with a 1k pull-up resistor. Once the charge current drops to 10% of the full scale current (C/10), the N-channel MOSFET is turned off
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and a 100A current source is connected to the CHRG pin. By forcing the OUT pin into a high impedance state, the current source will pull the pin low through the 100k resistor. When the internal timer has expired, the CHRG pin will change to high impedance state and the 100k resistor will then pull the pin high to indicate the charging has stopped. End of Charge (C/10) The LTC1731 includes a comparator to monitor the charge current to detect an end-of-charge condition. When the battery current falls below 10% of full scale, the comparator trips and turns off the N-channel MOSFET at the CHRG pin and switches in a 100A current source to ground. After an internal time delay of at least 300ms, this state is then latched. This delay will help prevent false triggering due to transient currents. The end-of-charge comparator is disabled in trickle charge mode. Gate Drive Typically the LTC1731 controls an external P-channel MOSFET to supply current to the battery. The DRV pin is internally clamped to 6.5V below VCC. This feature allows low voltage P-channel MOSFETs with gate to source breakdown voltage rated at 8V to be used. An external PNP transistor can also be used as the pass transistor instead of the P-channel MOSFET. Due to the low current gain of the current amplifier (CA), a high gain Darlington PNP transistor is required to avoid excessive charge current error. The gain of the current amplifier is around 0.6A/mV. For every 1A of base current, a 1.6mV of gain error shows up at the inputs of CA. With RPROG = 19.6k (100mV across RSENSE), it represents 1.67% of error in charging current. Constant-Current Only Mode The LTC1731 can be used as a programmable current source by forcing the TIMER pin to VCC. This is particularly useful for charging NiMH or NiCd batteries. In the constant-current only mode, the timer and voltage amplifier are both disabled. An external termination method is required to properly terminate the charge.
LTC1731-4.1
APPLICATIONS INFORMATION
Stability The charger is stable without any compensation when a P-channel MOSFET is used as the pass transistor. However, a 10F capacitor is recommended at the BAT pin to keep the ripple voltage low when the battery is disconnected. When a PNP transistor is chosen as the pass transistor, a 1000pF capacitor is required from the DRV pin to VCC. This capacitor is needed to help stablize the voltage loop. A 10F capacitor at the BAT pin is also recommended when a battery is not present.
PACKAGE DESCRIPTION
Dimensions in inches (millimeters) unless otherwise noted. MS8 Package 8-Lead Plastic MSOP
(LTC DWG # 05-08-1660)
0.118 0.004* (3.00 0.102)
0.040 0.006 (1.02 0.15) 0.007 (0.18) 0.021 0.006 (0.53 0.015) 0 - 6 TYP SEATING PLANE 0.012 (0.30) 0.0256 REF (0.65) BSC
* DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE ** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
S8 Package 8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.189 - 0.197* (4.801 - 5.004) 0.010 - 0.020 x 45 (0.254 - 0.508) 0.008 - 0.010 (0.203 - 0.254) 0- 8 TYP 0.053 - 0.069 (1.346 - 1.752) 8 0.004 - 0.010 (0.101 - 0.254) 0.228 - 0.244 (5.791 - 6.197) 0.150 - 0.157** (3.810 - 3.988) 7 6 5
0.014 - 0.019 (0.355 - 0.483) TYP *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
0.016 - 0.050 (0.406 - 1.270)
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0.034 0.004 (0.86 0.102)
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0.006 0.004 (0.15 0.102)
0.193 0.006 (4.90 0.15)
0.118 0.004** (3.00 0.102)
MSOP (MS8) 1098
1
23
4
0.050 (1.270) BSC
SO8 1298
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4
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LTC1731-4.1
TYPICAL APPLICATIONS
Linear Charger Using a PNP Transistor
VIN 5V TO 12V MBRM120T3 R2 1k C1 1nF R1 10k RSENSE 0.2 Q2 ZTX749 Q1 2N5087 IBAT = 500mA
CTIMER 0.1F
R5 1k LED
AVX0603ZC104KATIA
RELATED PARTS
PART NUMBER LT 1510-5 LT1512 LT1571 LT1620 LTC1729 LTC1731-4.2
(R)
DESCRIPTION 500kHz Constant-Voltage/Constant-Current Battery Charger SEPIC Battery Charger Battery Charger with Preset Voltage and Termination Flag Rail-to-Rail Current Sense Amplifier Termination Controller for Li-Ion Li-Ion Linear Battery Charge Controller
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Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 q FAX: (408) 434-0507 q www.linear-tech.com
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7 VCC SENSE 2 CHRG DRV 8 6
C3 1F
LTC1731-4.1 3 TIMER BAT PROG GND 4 1 5 RPROG 19.6k
+
Li-ION CELL
C2 10F
1731 TA02
1.5A Single-Cell Battery Charger
VIN = 5V ~ 6V D2 MBRS130LT3 C4 0.47F 7 VCC 2 CHRG SENSE 8 R2 4.7 5 6 3 2 TPS2829DBVR 22F CDRH6D38-220NC 1-CELL Li-Ion BATTERY + 4 R3 0.082 1/4W C2 22F CER
C5 1F CER
Q2 Si2305DS D1 MBRS130LT3
LTC1731-4.1 DRV 3 C1 0.1F
TIMER GND 4
BAT PROG 5 R4
1
18.2k 1%
+ -
C3 100F
1731 TA03
COMMENTS Most Compact, Up to 1.5A, Charges NiCd, NiMH, Li-Ion Cells VIN Can Be Higher or Lower Than Battery Voltage, 1.5A Switch Up to 1.5A; Preset Voltages: 4.1V, 4.2V, 8.2V, 8.4V Precise Output Current Programming, Up to 32V VOUT, Up to 10A IOUT Time or Charge Current Termination, Automatic Charger/Battery Detection, Status Output, Preconditioning, 8-Lead MSOP Fast Charge 4.2V Li-Ion Batteries with Constant-Voltage/ConstantCurrent Linear Charger
173141i LT/TP 0400 4K * PRINTED IN USA
(c) LINEAR TECHNOLOGY CORPORATION 2000

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