LTC1731-4.1 데이터 시트보기 (PDF) - Linear Technology

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LTC1731-4.1

Single Cell Lithium-Ion Linear Battery Charger Controllers

Linear Technology 

LTC1731-4.1/LTC1731-4.2

APPLICATIONS INFORMATION

After an internal time delay of 320ms, this state is then

latched. This delay will help prevent false triggering due to

transient currents. The end-of-charge comparator is dis-

abled 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 0.6µA/mV. For every 1µA 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 con-

stant-current only mode, the timer and voltage amplifier

are both disabled. An external termination method is

required to properly terminate the charge.

Stability

The charger is stable without any compensation when a

P-channel MOSFET is used as the pass transistor.

However, a 10µF 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

10µF capacitor at the BAT pin is also recommended when

a battery is not present.

TYPICAL APPLICATIO

Using CHRG Pin to Indicate Charge Status

OPTIONAL: FOR REVERSE

INPUT PROTECTION

VIN = 6V

MMSD4148

MMBT3906

MMBT3906

20k

CONDITION

NO WALL ADAPTER

CHARGING (I > C/10)

CHARGING (I < C/10)

TIMER EXPIRED

GREEN

OFF

OFF

ON

ON

AMBER

OFF

ON

OFF

OFF

1k

2.2k 1k

GREEN

AMBER

0.1µF

1.5k

MBRM120T3

7

4.7k

VCC

8

SENSE

2

CHRG

6

DRV

LTC1731-4.2

3

TIMER

1

BAT

5

PROG

GND

RPROG

4

19.6k

RSENSE

0.2Ω

Si9430DY

+ Li-ION

CELL

1µF

10µF

1731 TA04

9

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