ACT8796 datasheet(11/34 Pages) ACTIVE-SEMI

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SYSTEM MANAGEMENT

ACT8796

Rev1, 10-Oct-08

Innovative Power

- 11 -

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

ACT8796'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

The ACT8796 provides two manual enable/disable

inputs, PWRHLD and ON3. PWRHLD is the master

enable input. When driven high, PWRHLD enables

REG1, REG2, and REG4, and also activates the

enable/disable control logic for the other regulators.

ON3 is the enable input for REG3, and is active

when either of the following conditions exists:

1) nMSTR is asserted low, or

2) PWRHLD is asserted high.

Power-On Reset Output

The ACT8796 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. nRSTO asserts low upon startup and

remains low until the reset-timeout period expires,

at which point nRSTO goes high-Z.

nIRQ Output

Figure 2 shows two simple circuits that can be used

to generate nIRQ, a processor interrupt signal,

which can be used as part of the ACT8796’s push-

button control logic. This signal is typically used to

drive the interrupt input of the system processor,

and is useful in a variety of software-controlled en-

able/disable control routines. Figure 2A provides an

active-low, open-collector push-button status output

that sinks current when nMSTR is driven to a logic-

low. Figure 2B provides an active-high, open-

collector push-button status output that sources

current when nMSTR is driven to a logic-low.

Thermal Shutdown

The ACT8796 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 ACT8796 die temperature exceeds

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

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

FUNCTIONAL DESCRIPTION (CONT’D)

ACT8796

nMSTR

ACT8796

100k

nIRQ

OUT2

VCC

CPU

500k

OUT2

VCC

nIRQ

100k

INL

(A)

(B)

Figure 2:

Simple Circuits

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