ACT8798 datasheet(11/34 Pages) ACTIVE-SEMI

11 / 34 page

SYSTEM MANAGEMENT

ACT8798

Rev 1, 16-Nov-09

Innovative PowerTM

- 11 -

www.active-semi.com

ActivePMUTM is a trademark of Active-Semi.

I2CTM is a trademark of Philips Electronics.

Active-Semi

ACT8798'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

sequence.

Enable/Disable Inputs

The ACT8798 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 ACT8798 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

voltage 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 ACT8798’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

enable/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

ACT8798

integrates

thermal

shutdown

protection circuitry to prevent damage resulting from

excessive thermal stress, as may be encountered

under fault conditions. This circuitry disables all

regulators if the ACT8798 die temperature exceeds

160°C, and prevents the regulators from being

enabled until the IC temperature drops by 20°C

(typ).

FUNCTIONAL DESCRIPTION (CONT’D)

Figure 2:

Simple Circuits

ACT8798

nMSTR

ACT8798

100k

nIRQ

OUT2

VCC

CPU

500k

OUT2

VCC

nIRQ

100k

INL

(A)

(B)

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