ACT8740 datasheet(37/40 Pages) ACTIVE-SEMI

37 / 40 page

SINGLE-CELL Li+ BATTERY CHARGER (CHGR)

ACT8740

Rev PrB, 25-Feb-08

Innovative Products. Active Solutions.

- 37 -

www.active-semi.com

ActivePMU

TM is a trademark of Active-Semi.

2CTM is a trademark of Philips Electronics.

General Description

The ACT8740’s internal battery charger is a full-

featured, intelligent, linear-mode, single-cell charger

for Lithium-based cells. This charger provides a

complete selection of advanced functions and re-

quires minimum system design effort.

The core of the charger is a CC/CV (Constant- Cur-

rent/Constant-Voltage), linear-mode charge control-

ler with a highly-accurate charge termination thresh-

old. This controller incorporates current and voltage

sense circuitry, an internal power MOSFET, a full-

featured state-machine that implements charge

control and safety features, and circuitry that elimi-

nates the reverse-blocking diode required by con-

ventional charger designs. The ACT8740’s charger

also features thermal-regulation circuitry that pro-

tects it against excessive junction temperature, al-

lowing the fastest possible charging times, as well

as proprietary input protection circuitry that makes

the charger robust against input voltage transients

that can damage other chargers.

CC/CV Regulation Loop

At the core of the ACT8740’s battery charger is a

CC/CV regulation loop, which regulates either cur-

rent or voltage as necessary to ensure fast and safe

charging of the battery. In a normal charge cycle,

this loop regulates the charge current to the pro-

grammed charge current level and continues charg-

ing at this current until the battery cell voltage

reaches the charge termination voltage. Once the

cell reaches the Charge-Termination Threshold

Voltage, the CV loop takes over and charge current

is allowed to decrease as necessary to keep the

cell voltage at the charge termination voltage.

Charger Enable/Disable

When a valid input voltage is applied to VIN, the

battery charger is automatically enabled in order to

simplify system design and eliminate the need for

external input supply detection circuitry.

Once the charger is enabled, a charge cycle auto-

matically begins unless CHGLEV is floating,

CHGR/SUSCHG[ ] is set to [1], or a fault condition

has occurred.

Charger Status

During normal operation, the processor can read

the status of the input supply by reading

CHGR/VINPOK[ ], which is set to [1] when the fol-

lowing conditions are true:

1) The voltage at VIN is greater than the voltage at

BAT, and

2) The voltage at VIN is greater than the VIN

UVLO threshold.

Alternatively, the processor can read the status of the

charger by reading the CHGR/CHGROK[ ] bit, which

is set to [1] when the following conditions are true:

1) The voltage at VIN is greater than the voltage at

BAT, and

2) The voltage at VIN is greater than the VIN

UVLO threshold, and

3) No fault has occurred.

Finally, the status of a charge cycle can be deter-

mine by reading the CHGR/CHGSTAT[ ] bit or by

evaluating the state of the nSTAT output. nSTAT is

an open-drain output that has an internal 8mA cur-

rent limit, and is capable of directly driving LEDs for

a visual charge-status indication without the need of

current-limiting resistors or other external circuitry.

To drive an LED, simply connect the LED between

an appropriate supply, typically VIN, and nSTAT.

When a logic-level charge status indicator is de-

sired, simply connect a pull-up resistor of 10kΩ or

more from nSTAT to OUT2 or another suitable sup-

ply.

CHGR/CHGSTAT[ ] is set to [1] and nSTAT sinks

current when any of the following conditions are

true:

1) The charger is operating in the PRECONDI-

TION state, or

2) The charger is operating in the FAST-CHARGE

state, or

3) The charger is operating in the TOP-OFF state.

When none of these conditions are true, CHGR/

CHGSTAT[ ] is cleared to [0] and nSTAT goes into

a high-Z state.

FUNCTIONAL DESCRIPTION

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