LTC1732-8.4 View Datasheet(PDF) - Linear Technology

Part Name

Description

Manufacturer

LTC1732-8.4

Lithium-Ion Linear Battery Charger Controller

Linear Technology 

LTC1732-8.4

APPLICATIONS INFORMATION

V+

VDD

8

VCC

3

CHRG

400k

2k

µPROCESSOR

OUT

LTC1732-8.4

IN

1732-8.4 F01

Figure 1. Microprocessor Interface

Table 1. Microprocessor Interface

IN

OUT CHARGE STATUS

LOW

HIGH Charge

LOW

Hi-Z C/10

HIGH

Hi-Z Stop Charging

When the LTC1732-8.4 is in charge mode, the CHRG pin

is pulled low 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 full-

scale current (C/10), the N-channel MOSFET is turned off

and a 35µA current source is connected to the CHRG pin.

The IN pin is then pulled high by the 2k pull-up. By forcing

the OUT pin into a high impedance state, the current

source pulls the pin low through the 400k resistor. When

the internal timer has expired, the CHRG pin changes to

high impedance and the 400k resistor pulls the pin high to

indicate that charging has stopped.

ACPR Output Pin

The LTC1732-8.4 has an ACPR output pin to indicate that

the input supply (wall adapter) is higher than 8.2V and

55mV above the voltage at the BAT pin. When both

conditions are met, the ACPR pin is pulled to ground by an

N-channel MOSFET that is capable of driving an LED.

Otherwise, this pin is high impedance.

CHRG Status Output Pin (C/10)

The LTC1732-8.4 includes a comparator to monitor the

charge current to detect a near end-of-charge condition.

This comparator does not terminate the charge cycle, but

provides an output signal to indicate a near full charge

condition. The timer is used to terminate the charge cycle.

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 35µA current source to

ground. After an internal time delay of 15ms, this state is

latched. This delay helps prevent false triggering due to

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

abled in trickle charge mode.

Gate Drive

Typically the LTC1732-8.4 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 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.

17328f

9

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