ACT8937A datasheet(43/45 Pages) ACTIVE-SEMI

43 / 45 page

ACT8937A

Rev 1, 22-Oct-12

Innovative Power

ActivePMU

TM and ActivePathTM are trademarks of Active-Semi.

2CTM is a trademark of NXP.

- 43 -

www.active-semi.com

TOTTIMO[1]

TOTTIMO[0]

TOTAL TIME-OUT

PERIOD

3 hrs

4 hrs

5 hrs

Disabled

Thermal Regulation

The charger features an internal thermal regulation

loop that monitors die temperature and reduces

charging current as needed to ensure that the die

temperature does not exceed the thermal regulation

threshold of 110°C. This feature protects against

excessive junction temperature and makes the

device more accommodating to aggressive thermal

designs. Note, however, that attention to good

thermal designs is required to achieve the fastest

possible charge time by maximizing charge current.

Charge Safety Timers

The charger features programmable charge safety

timers which help ensure a safe charge by

detecting potentially damaged cells. These timers

are programmable via the PRETIMO[1:0] and

TOTTIMO[1:0] bits, as shown in Table 12 and Table

13. Note that in order to account for reduced charge

current resulting from DCCC operation, the charge

time-out periods are extended proportionally to the

reduction in charge current. As a result, the actual

safety period may exceed the nominal timer period.

Charger Timer Interrupts

The charger features the ability to generate

interrupts based upon the status of the charge

timers. Set the TIMRPRE[ ] bit to 1 and

TIMRSTAT[ ] bit to 1 to generate an interrupt when

the Precondition Timer expires. Set the TIMRTOT[ ]

bit to 1 and TIMRSTAT[ ] bit to 1 to generate an

interrupt when the Total-Charge Timer expires.

TIMRDAT[ ] indicates the status of the charge

timers. A value of 1 indicates a precondition time-

out or a total charge time-out occurs, a value of 0

indicates other cases.

When an interrupt is generated by the charge

timers, reading the TIMRSTAT[ ] returns a value of

1. TIMRSTAT[ ] is automatically cleared to 0 upon

reading. When no interrupt is generated by the

charge timers, reading the TIMRSTAT[ ] returns a

value of 0.

Table 12:

PRECONDITION Safety Timer Setting

Table 13:

Total Safety Timer Setting

Charge Status Indicator

The charger provides a charge-status indicator

output, nSTAT. nSTAT is an open-drain output

which sinks current when the charger is in an

active-charging state, and is high-Z otherwise.

nSTAT features an internal 8mA current limit, and is

capable of directly driving a LED without the need

of a current-limiting resistor or other external

circuitry. To drive an LED, simply connect the LED

between nSTAT pin and an appropriate supply,

such as VSYS. For a logic-level charge status

indication, simply connect a resistor from nSTAT to

an appropriate voltage supply.

Table 14:

Charging Status Indication

Reverse-Current Protection

The charger includes internal reverse-current

protection 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 CHGIN falls

below VBAT, the charger automatically reconfigures

its power switch to minimize current drawn from the

battery.

Battery Temperature Monitoring

In a typical application, the TH pin is connected to

the battery pack's thermistor input, as shown in

PRETIMO[1]

PRETIMO[0]

PRECONDITION

TIME-OUT PERIOD

40 mins

60 mins

80 mins

Disabled

STATE

nSTAT

PRECONDITION

Active

FAST-CHARGE

Active

TOP-OFF

Active

END-OF-CHARGE

High-Z

SUSPEND

High-Z

TEMPERATURE FAULT

High-Z

TIME-OUT-FAULT

High-Z

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