Datasheet

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LTC1731-8.2/LTC1731-8.4

sn1731 17318fs

FEATURES

APPLICATIO S

DESCRIPTIO

TYPICAL APPLICATIO

Lithium-Ion Linear

Battery Charger Controller

The LTC

1731-8.2/LTC1731-8.4 are complete constant-

current/constant-voltage linear charger controllers for 2-

cell lithium-ion (Li-Ion)batteries. Nickel-cadmium (NiCd)

and nickel-metal-hydride (NiMH) batteries can also be

charged with constant current using external termina-

tion. The external sense resistor sets the charge current

with 7% accuracy. An internal resistor divider and preci-

sion reference set the final float potential with 1% accu-

racy. The output float voltages are set internally to 8.2V

(LTC1731-8.2) or 8.4V (LTC1731-8.4).

When the input supply is removed, the LTC1731-8.2/

LTC1731-8.4 automatically enter a low current sleep mode,

dropping the battery drain current to typically 15µA. An

internal comparator detects the end-of-charge (C/10) con-

dition while a programmable timer, using an external

capacitor, sets the total charge time. Fully discharged cells

are automatically trickle charged at 10% of the pro-

grammed current until battery voltage exceeds 4.95V.

The LTC1731-8.2/LTC1731-8.4 are available in the 8-pin

MSOP and SO packages. For 1-cell Li-Ion battery charg-

ing, see the LTC1731-4.1 and LTC1731-4.2 data sheets.

■

Complete Linear Charger Controller for

2-Cell Lithium-Ion Batteries

■

1% Voltage Accuracy

■

Programmable Charge Current

■

C/10 Charge Current Detection Output

■

Programmable Charge Termination Timer

■

Space Saving 8-Pin MSOP Package

■

Automatic Sleep Mode When Input Supply

is Removed (15µA Battery Drain)

■

Automatic Trickle Charging of Low Voltage Cells

■

Programmable for Constant-Current-Only Mode

■

Cellular Phones

■

Handheld Computers

■

Charging Docks and Cradles

■

Programmable Current Source

, LTC and LT are registered trademarks of Linear Technology Corporation.

400mA Li-Ion Charger

= 9V

SENSE

DRV

SENSE

0.2Ω

PROG

19.6k

2-CELL

Li-ION

LTC1731-8.4

*SHUTDOWN INVOKED BY FLOATING THE PROG PIN

BAT

CHRG

MBRM120T3

10µF

1731 TA01

1µF

BAT

= 400mA

TIMER

0.1µF

Si9430DY

TIMER

PROG

GND

CHARGE

STATUS

Typical Li-Ion Charge Cycle

TIME (HOURS)

CHARGE CURRENT (mA)

400

300

200

100

1.5 2.5

1731 TA01b

0.5 1.0

2.0 3.0

CONSTANT

VOLTAGE

CONSTANT

CURRENT

TIMER

STOPS

CHRG

LED OFF

BATTERY VOLTAGE

400mA HR BATTERY

CHARGE CURRENT

BATTERY VOLTAGE(V)

Summary of content (12 pages)

PAGE 1
LTC1731-8.2/LTC1731-8.4 Lithium-Ion Linear Battery Charger Controller U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO The LTC ®1731-8.2/LTC1731-8.4 are complete constantcurrent/constant-voltage linear charger controllers for 2cell lithium-ion (Li-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 7% accuracy.
PAGE 2
LTC1731-8.2/LTC1731-8.4 W W U W ABSOLUTE MAXIMUM RATINGS (Note 1) Input Supply Voltage (VCC) ................................... 13.2V SENSE, DRV, BAT, TIMER, PROG ............ – 0.3V to VCC CHRG ..................................................... – 0.3V to 13.2V Operating Temperature Range (Note 2) .....– 40° to 85°C Storage Temperature Range ................. – 65°C to 150°C Lead Temperature (Soldering, 10 sec)..................
PAGE 3
LTC1731-8.2/LTC1731-8.4 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 9V unless otherwise noted. SYMBOL PARAMETER CONDITIONS VASD Automatic Shutdown Threshold Voltage (VCC – VBAT) Falling (VCC – VBAT) Rising MIN TYP MAX UNITS 30 40 54 69 90 100 mV mV VDIS Voltage Mode Disable Threshold Voltage VDIS = (VCC – VTIMER) 0.
PAGE 4
LTC1731-8.2/LTC1731-8.4 U W TYPICAL PERFOR A CE CHARACTERISTICS Trickle Charge Threshold Voltage vs Temperature Timer Accuracy vs VCC 4.94 110 VCC = 9V CTIMER = 0.1µF VBAT = 6V TA = 25° CTIMER = 0.1µF VCC = 9V 105 4.92 4.91 tTIMER (%) 105 tTIMER (%) VTRKL (V) 4.93 Timer Accuracy vs Temperature 110 100 95 95 4.90 –50 –25 25 0 75 50 100 90 125 9 10 11 75 540 530 520 125 Program Pin Voltage vs VCC 2.48 RPROG = 19.6K RSENSE = 0.2Ω VBAT = 6V VCC = 9V RPROG = 19.
PAGE 5
LTC1731-8.2/LTC1731-8.4 U U U PIN FUNCTIONS BAT (Pin 1): Battery Sense Input. A bypass capacitor of at least 10µF is required to keep the loop stable when the battery is not connected. A precision internal resistive 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.
PAGE 6
LTC1731-8.2/LTC1731-8.4 W BLOCK DIAGRA VCC 7 RSENSE SENSE + 80Ω C1 2 + – 800Ω – CHRG 8 54mV + C4 – – C/10 STOP C/10 TIMER + DRV CA SLP OSCILLATOR BAT – SHDN 3 720Ω LOGIC LBO COUNTER 6 1 C2 + 100µA 4.9V VREF – + – VA VCC A1 – + + C3 VREF 2.457V 2.5µA CHARGE 5 BATTERY CURRENT IBAT = (2.
PAGE 7
LTC1731-8.2/LTC1731-8.4 U OPERATIO The LTC1731-8.2/LTC1731-8.4 are linear battery charger controllers. 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 800Ω resistor that creates a voltage drop from VCC to the input of the current amplifier (CA).
PAGE 8
LTC1731-8.2/LTC1731-8.4 U W U U APPLICATIONS INFORMATION Charger Conditions The charger is off when any of the following conditions exist: the VCC pin is less than 8.2V, the droput voltage (VCC - VBAT) is less than 54mV, the PROG pin is floating, or the timer has ended. The DRV pin will be pulled to VCC and the internal resistor divider is disconnected to reduce the current drain on the battery.
PAGE 9
LTC1731-8.2/LTC1731-8.4 U W U U APPLICATIONS INFORMATION When the LTC1731 is in the charge mode, the CHRG pin is pulled to ground 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 2k pull-up resistor. Once the charge current drops to 10% of the fullscale current (C/10), the N-channel MOSFET is turned off and a 100µA current source is connected to the CHRG pin.
PAGE 10
LTC1731-8.2/LTC1731-8.4 U PACKAGE DESCRIPTION MS8 Package 8-Lead Plastic MSOP (Reference LTC DWG # 05-08-1660) 0.889 ± 0.127 (.035 ± .005) 5.23 (.206) MIN 3.2 – 3.45 (.126 – .136) 0.42 ± 0.04 (.0165 ± .0015) TYP 3.00 ± 0.102 (.118 ± .004) (NOTE 3) 0.65 (.0256) BSC 8 7 6 5 0.52 (.206) REF RECOMMENDED SOLDER PAD LAYOUT 0.254 (.010) 3.00 ± 0.102 (.118 ± .004) NOTE 4 4.88 ± 0.1 (.192 ± .004) DETAIL “A” 0° – 6° TYP GAUGE PLANE 0.53 ± 0.015 (.021 ± .006) DETAIL “A” 1 2 3 4 1.10 (.
PAGE 11
LTC1731-8.2/LTC1731-8.4 U PACKAGE DESCRIPTION S8 Package 8-Lead Plastic Small Outline (Narrow .150 Inch) (Reference LTC DWG # 05-08-1610) 0.189 – 0.197* (4.801 – 5.004) 8 7 6 5 0.150 – 0.157** (3.810 – 3.988) 0.228 – 0.244 (5.791 – 6.197) SO8 1298 1 0.010 – 0.020 × 45° (0.254 – 0.508) 0.008 – 0.010 (0.203 – 0.254) 0.053 – 0.069 (1.346 – 1.752) 0°– 8° TYP 0.016 – 0.050 (0.406 – 1.270) 0.014 – 0.019 (0.355 – 0.483) TYP *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.
PAGE 12
LTC1731-8.2/LTC1731-8.4 U TYPICAL APPLICATIO Linear Charger Using a PNP Transistor VIN = 9V MBRM120T3 R2 2k C1 1nF 7 CHARGE STATUS VCC SENSE 2 DRV CHRG R1 10k RSENSE 0.25Ω Q2 ZTX749 8 6 Q1 2N5087 LTC1731-8.4 3 TIMER CTIMER* 0.1µF BAT PROG C3 1µF IBAT = 400mA 1 5 GND + RPROG 19.6k 4 2-CELL Li-ION *AVX 0603ZC104KAT1A C2 10µF 1731 TA02 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT®1510-5 500kHz Constant-Voltage/Constant-Current Battery Charger Most Compact, Up to 1.