LTC1732-4.2 Ver la hoja de datos (PDF) - Linear Technology

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Fabricante

LTC1732-4.2

Lithium-Ion Linear Battery Charger Controller

Linear Technology 

LTC1732-4/LTC1732-4.2

APPLICATIONS INFORMATION

Gate Drive

Typically the LTC1732 controls an external P-channel

MOSFET to supply current to the battery. An external PNP

transistor can also be used as the pass transistor instead

of the P-channel MOSFET. Due to the low transconductance

of the current amplifier (CA), a high gain Darlington PNP

transistor is required to avoid excessive charge current

error. The transconductance 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). This represents a 1.6%

error in charge current.

Constant-Current Only Mode

The LTC1732 can be used as a programmable current

source by connecting 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

TYPICAL APPLICATIO S

amplifier are both disabled. An external termination method

is required to properly terminate the charging by floating

the PROG pin.

Stability

The charger is stable without any compensation when a

P-channel MOSFET is used as the pass transistor and

the battery is present. A 10µF tantalum capacitor is

recommended at the BAT pin to keep the ripple voltage

low when the battery is disconnected. A ceramic output

capacitor may also be used, but because of the very low

ESR and high Q characteristics of multilayer ceramic

capacitors, it may be necessary to add a 1Ω resistor in

series with the ceramic capacitor to improve voltage

mode stability.

If a PNP transistor is used for the pass transistor, a 1000pF

capacitor is required from the DRV pin to VCC. To help

stablize the voltage loop a 10µF tantalum capacitor at the

BAT pin is also recommended when a battery is not

present.

Li-Ion Linear Charger Using a PNP Transistor

VIN = 6V

MBRM120T3

R1

1k

CTIMER

0.1µF

R2

1k

8

VCC

3

9

CHRG SENSE

10

ACPR

DRV 7

LTC1732-4

4

TIMER

1

BAT

6

PROG

SEL GND

2

5

C1 R3

RSENSE

C3

1nF 10k 0.2Ω

1µF

Q2

ZTX749

Q1

2N5087

IBAT = 500mA

RPROG

19.6k

C2

10µF

+ 4.1V

Li-Ion

CELL

1732 TA02

10

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