ACT8342
SYSTEM MANAGEMENT
FUNCTIONAL DESCRIPTION
General Description
The ACT8342 offers an array of system manage-
ment functions that allow it to provide optimal per-
formance in a wide range of applications.
Rev0, 26-May-08
System Startup and Shutdown
The ACT8342 features a flexible control architec-
ture that supports a variety of software-controlled
enable/disable functions that make it a simple yet
flexible and highly configurable solution.
The ACT8342 is automatically enabled when any of
the following conditions exists:
1) nMSTR is asserted low, or
2) ON1 is asserted high, or
3) ON2 is asserted high, or
4) ON3 is asserted high.
If any of these conditions is true, the ACT8342 en-
ables and ON1 drives REG1, ON2 drives REG2,
and ON3 drives REG3.
Manual Enable Due to Asserting nMSTR Low
System startup is initiated when the user presses
the push-button, asserting nMSTR low. When this
occurs, REG1 is enabled, which in turn enables the
processor to allow it to control the system power up
sequence. Once the power-up routine is success-
fully completed, the microprocessor must assert
ON1 so that the ACT8342 remains enabled after
the push-button is released by the user. Upon com-
pletion of the start-up sequence the processor as-
sumes control of the power system and all further
operation is software-controlled.
Manual Enable Due to Asserting ON1 High
The ACT8342 is compatible with applications that
do not utilize it’s push-button control function, and
may be enabled by simply driving ON1 to a logic-
high. In this case, the signal driving ON1 controls
enable/disable timing, although software-controlled
enable/disable sequences are still supported if the
processor assumes control of the power system
once the startup sequence is completed.
Shutdown Sequence
Once a successful power-up routine is completed,
the system processor controls the operation of the
power system, including the system shutdown tim-
Innovative Power
TM
ActivePMU
TM
ing and sequence. The ACT8342 asserts nIRQ low
when nMSTR is asserted low, providing a simple
means of alerting the system processor when the
user wishes to shut the system down. Asserting
nIRQ interrupts the system processor, initiating an
interrupt service routine in the processor which will
reveal that the user pressed the push-button. The
microprocessor may validate the input, such as by
ensuring that the push-button is asserted for a mini-
mum amount of time, then initiates a software-
controlled power-down routine, the final step of
which is to de-assert the ON1 input, disabling
REG1 and REG2 and shutting the system down.
nMSTR Enable Input
In most applications, connect nMSTR to an active
low, momentary push-button switch to utilize the
ACT8342’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 ACT8342 provides three manual en-
able/disable inputs. When driven high, ON1 enables
REG1, ON2 enables REG2, and ON3 enables
OUT3.
nIRQ Output
The ACT8342 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 ACT8342 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 ACT8342 die temperature exceeds
160°C, and prevents the regulators from being en-
abled until the IC temperature drops by 20°C (typ).
-7-
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