ACT8828 datasheet(45/49 Pages) ACTIVE-SEMI

45 / 49 page

ActivePath

TM CHARGER

ACT8828

Rev 3, 24-Sep-09

Active-Semi

Innovative Power

- 45 -

www.active-semi.com

ActivePMU

TM and ActivePathTM are trademarks of Active-Semi.

2CTM is a trademark of Philips Electronics.

STATE

nSTAT

Charging

Discharging

OFF

Input Floating

OFF

Fault

OFF

Charging Complete

OFF

FUNCTIONAL DESCRIPTION CONT’D

Thermal Regulation

The ACT8828's ActivePath charger features an

internal thermal regulation loop that reduces the

charging current as necessary to ensure that the

die temperature does not rise beyond the thermal

regulation threshold of 110°C. This feature protects

the against excessive junction temperature and

makes

the

device

accommodating

aggressive thermal designs. Note, however, that

attention to good thermal designs is required to

achieve the fastest possible charge time by

maximizing charge current.

In order to account for the reduced charge current

resulting from operation in thermal regulation mode,

the

charge

timeout

periods

are

extended

proportionally to the reduction in charge current.

Charging Safety Timers

The ACT8828 features a safety timer that is

programmable via an external resistor (RBTR)

connected from BTR to GA. The timeout period is

calculated as a function of this resistor by the

following equation:

tCHG = KBTR × RBTR, where KBTR = 0.24s/Ω.

If the timeout period expires prior to charge

termination, the charger is disabled and the nSTAT

pin signal a fault condition. If the ACT8828 detects

that the charger remains in precondition for longer

than the precondition time out period (which

determined as tCHG/3), the ACT8828 turns off the

charger and generate a FAULT to ensure prevent

charging a bad cell.

Charging Status Indication

The ACT8828 provides one charge-status output,

nSTAT which indicates charge status as defined in

Table 17. nSTAT is open-drain output with internal

5mA current limits, which sinks current when

asserted and are high-Z otherwise, and is capable

of directly driving LED without the need of current-

limiting resistor or other external circuitry. To drive

an LED, simply connect the LED between nSTAT

pin and an appropriate supply (typically VSYS). For

a logic level indication, simply connect a resistor

from nSTAT to a appropriate voltage supply.

Table 17:

Charging Status Indication Table

Input Supply Detection

The ACT8828's ActivePath charger is capable of

withstanding voltages of up to 12V, protecting the

system from fault conditions such as input voltage

transients or application of an incorrect input

supply. Although the ACT8828 can withstand a

wide range of input voltages, valid input voltages for

charging must be greater than the under-voltage

lockout voltage (UVLO) and the over-voltage

protection (OVP) thresholds, as described below.

Under Voltage Lock Output (UVLO)

Whenever the input voltage applied to CHG_IN falls

below 3.8V (typ), an input under-voltage condition is

detected and the charger is disabled. Once an input

under-voltage condition is detected, the input must

exceed the under-voltage threshold by at least

800mV for charging to resume.

Over Voltage Protection (OVP)

If the charger detects that the voltage applied to

CHG_IN exceeds 6.8V (typ), an over-voltage

condition is detected and the charger is disabled.

Once an input over-voltage condition is detected,

the input must fall below the OVP threshold by at

least 400mV for charging to resume.

Reverse Leakage Current

The ACT8828's ActivePath charger includes

internal circuitry that eliminates the need for

blocking diodes, reducing solution size and cost as

well as dropout voltage relative to conventional

battery chargers. When the voltage at CHG_IN falls

below VBAT, the charger automatically reconfigures

its power switch to minimize current drain from the

battery

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