ACT8712 datasheet(13/36 Pages) ACTIVE-SEMI

13 / 36 page

SYSTEM MANAGEMENT

Rev0, 25-Feb-08

ACT8712

Innovative Products. Active Solutions.

- 13 -

www.active-semi.com

ActivePMU

TM is a trademark of Active-Semi.

2CTM is a trademark of Philips Electronics.

nMSTR Enable Input

In most applications, connect nMSTR to an active

low, momentary push-button switch to utilize the

ACT8712’s closed-loop enable/disable functionality.

If a momentary-on switch is not used, drive nMSTR

to GA or to a logic low to initiate a startup se-

quence.

Enable/Disable Inputs (ON1 and ON2)

The ACT8712 provides two manual enable/disable

inputs, ON1 and ON2. ON1 is the master enable

input. When driven high, ON1 enables REG1 and

REG2. ON2 is the enable input for REG3. ON2 is

used to enable REG3 when any of the following

conditions exists:

1) A valid supply voltage is present at VIN,

2) nMSTR is asserted low, or

3) ON1 is asserted high.

Power-On Reset Output

The ACT8712 integrates a 260ms power-on reset

generator, reducing system size and cost. nRSTO

is an open-drain output. Connect a 10kΩ or greater

pull-up resistor from nRSTO to an appropriate volt-

age supply, typically OUT2. nRSTO asserts low

upon startup and remains low until the reset-timeout

period expires, at which point nRSTO goes high-Z.

nIRQ Output

The ACT8712 provides an active-low, open-drain

push-button status output that sinks current when

nMSTR is driven to a logic-low. Connect a pull-up

resistor from nIRQ to an appropriate voltage supply.

nIRQ is typically used to drive the interrupt input of

the system processor, and is useful in a variety of

software-controlled enable/disable control routines.

Thermal Shutdown

The ACT8712 integrates thermal shutdown protec-

tion circuitry to prevent damage resulting from ex-

cessive thermal stress, as may be encountered un-

der fault conditions. This circuitry disables all regu-

lators if the ACT8712 die temperature exceeds

160°C, and prevents the regulators from being en-

abled until the IC temperature drops by 20°C (typ).

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