ACT8342
Rev 3, 11-Sep-09
SYSTEM MANAGEMENT
FUNCTIONAL DESCRIPTION
General Description
The ACT8342 offers an array of system
management functions that allow it to provide
optimal performance in a wide range of
applications.
timing 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 minimum 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
sequence.
Enable/Disable Inputs
The ACT8342 provides three manual
enable/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
protection circuitry to prevent damage resulting
from excessive thermal stress, as may be
encountered under fault conditions. This circuitry
disables all regulators if the ACT8342 die
temperature exceeds 160°C, and prevents the
regulators from being enabled until the IC
temperature drops by 20°C (typ).
System Startup and Shutdown
The ACT8342 features a flexible control
architecture 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
enables 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
successfully completed, the microprocessor must
assert ON1 so that the ACT8342 remains enabled
after the push-button is released by the user. Upon
completion of the start-up sequence the processor
assumes 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
Innovative Power
TM
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TM
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