ACT8796
Active- Semi
Rev 2, 16-Nov-09
SYSTEM MANAGEMENT
FUNCTIONAL DESCRIPTION (CONT’D)
nMSTR Enable Input
nIRQ Output
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
sequence.
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
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.
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:
Thermal Shutdown
The ACT8796 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 ACT8796 die temperature exceeds
160°C, and prevents the regulators from being
enabled until the IC temperature drops by 20°C
(typ).
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 10kꢀ 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.
Figure 2:
Simple Circuits
nMSTR
OUT2
INL
ACT8796
VCC
100k
100k
500k
OUT2
PB
VCC
100k
nIRQ
nIRQ
100k
PB
ACT8796
CPU
(A)
(B)
Innovative PowerTM
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