ACT8712 datasheet(34/36 Pages) ACTIVE-SEMI

34 / 36 page

SINGLE-CELL Li+ BATTERY CHARGER (CHGR)

Rev0, 25-Feb-08

ACT8712

Innovative Products. Active Solutions.

- 34 -

www.active-semi.com

ActivePMU

TM is a trademark of Active-Semi.

2CTM is a trademark of Philips Electronics.

Input Capacitor Selection

VIN is the power input pin for the ACT8712 battery

charger. The battery charger is automatically en-

abled whenever a valid voltage is present on VIN.

In most applications, VIN is connected to either a

wall adapter or a USB port. Under normal opera-

tion, the input of the charger will often be “hot-

plugged” directly to a powered USB or a wall

adapter cable, and supply voltage ringing and over-

shoot may appear at the VIN pin and can potentially

be large enough to damage the charger input. In

most applications, a capacitor connected from VIN

to GA, placed as close as possible to the IC, is suf-

ficient to absorb the energy. The VIN pin is de-

signed for enhanced robustness and has an abso-

lute maximum transient voltage rating of +7V, and

attention must be given to bypass techniques to

ensure operation within this limit.

Charge Current Programming

Charge current programming is performed using a

combination of the ACT8712’s CHGR/ISET1[ ] and

CHGR/ISET2[e] registers and the multifunction

CHGLEV input. The multi-function CHGLEV input

provides charge-current selection between the cur-

rent setting defined by CHGR/ISET1[ ] and the cur-

rent setting programmed by CHGR/ISET2[ ], as well

as a charge suspend function. Drive CHGLEV to a

logic-low to select the current programmed by

CHGR/ISET1[ ]. In order to reduce the number of

GPIOs required to interface with the ACT8712, the

CHGR/ICHGSET[ ] bit may be used instead of the

CHGLEV pin to achieve identical functionality.

By default, the ACT8712’s CHGR/ISET1[ ] and

CHGR/ISET2[ ] registers are programmed to pro-

vide a charge current of 90mA when CHGLEV is

driven low, and 450mA when CHGLEV is driven

high, so that the ACT8712 is compatible with sys-

tem that utilize lower-current input supplies, such as

a USB port. To achieve a different charge current,

program the CHGR/ISET1[ ] and/or CHGR/ISET2[ ]

registers accordingly.

Charge Safety Timer

The ACT8712 features a programmable charge

safety timer that is utilized during operation in the

PRECONDITION state. The safety timer has a de-

fault timeout period of 60 minutes, although it may

be programmed to either 90 minutes or 120 minutes

by writing to the CHGR/TIMOSET[ ] register. This

applications that do not require a charge safety

timer function.

Thermal Regulation

The ACT8712 features an internal thermal feedback

loop that reduces the charging current as necessary

to ensure that the die temperature does not exceed

the thermal regulation threshold of 110°C. This fea-

ture protects the ACT8712 against excessive junc-

tion temperature and makes the ACT8712 more

accommodating of aggressive thermal designs with-

out risk of damage. Note, however, that attention to

good thermal design is required to achieve the

shortest possible charge time.

Charge Status Bits

The ACT8712 charger provides a variety of read-

only charge status bits that can be read by the host

processor as needed to make intelligent power

management decisions. Five charge status bits are

available:

Input Voltage Status

The CHGR/VINPOK[ ] bit is set to [1] when a valid

input supply is connected to VIN. A valid input sup-

ply is defined as one that :

1) is greater than the voltage at BAT, and

2) is greater than the VIN UVLO threshold.

Charger Status

There are two bits available that describe the cur-

rent status of the charger itself.

The CHGR/CHGSTAT[ ] bit is set to [1] when the

charger is actively charging the battery, and is

cleared to [0] when a charge cycle terminates or is

suspended.

The CHGR/CHGROK[ ] bit is set to [1] when TBD,

and is cleared otherwise.

Timeout Fault

The CHGR/TIMOFLT[ ] bit is set to [1] when a time-

out fault occurs, and remains cleared otherwise.

Once set to [1], it is automatically cleared to [0]

when TBD.

Battery Removed Fault

The CHGR/BATFLT[ ] bit is set to [1] when there is

no battery connected, and remains cleared other-

wise.

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