ACT8798 View Datasheet(PDF) - Active-Semi, Inc

Part Name

Description

Manufacturer

ACT8798

Six Channel Integrated Power Management IC for Handheld Portable Equipment

Active-Semi, Inc 

Active-Semi

ACT8798

Rev 1, 16-Nov-09

SYSTEM MANAGEMENT

FUNCTIONAL DESCRIPTION

General Description

The ACT8798 offers an array of system

management functions that allow it to provide

optimal performance in a wide range of

applications.

I2C Serial Interface

At the core of the ACT8798's flexible architecture is

an I2C interface that permits optional programming

capability to enhance overall system performance.

To ensure compatibility with a wide range of system

processors, the ACT8798 uses standard I2C

commands; I2C write-byte commands are used to

program the ACT8798, and I2C read-byte

commands are used to read the ACT8798's internal

registers. The ACT8798 always operates as a slave

device, and is addressed using a 7-bit slave

address followed by an eighth bit, which indicates

whether the transaction is a read-operation or a

write-operation, [1011011x].

SDA is a bi-directional data line and SCL is a clock

input. The master initiates a transaction by issuing a

START condition, defined by SDA transitioning from

high to low while SCL is high. Data is transferred in

8-bit packets, beginning with the MSB, and is

clocked-in on the rising edge of SCL. Each packet

of data is followed by an Acknowledge (ACK) bit,

used to confirm that the data was transmitted

successfully.

For more information regarding the I2C 2-wire serial

interface, go to the NXP website: http://www.nxp.com

System Startup and Shutdown

The ACT8798 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 ACT8798 is automatically enabled when either

of the following conditions exists:

1) nMSTR is asserted low, or

2) PWRHLD is asserted high.

If either of these conditions is true, the ACT8798

enables REG1, REG2, REG4, and may be REG3,

powering up the system processor so that the

startup and shutdown sequences may be controlled

via software. These startup conditions are

described in detail below.

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, REG2, REG3, and REG4 are

enabled and nRSTO is asserted low to hold the

microprocessor in RESET for 260ms. nRSTO goes

high-Z upon expiration of the reset timer, de-

asserting the processor's reset input and allowing

the microprocessor to initiate its power up

sequence. Once the power-up routine is

successfully completed, the microprocessor must

assert PWRHLD so that the ACT8798 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 PWRHLD High

The ACT8798 is compatible with applications that

do not utilize its push-button control function, and

may be enabled by simply driving PWRHLD to a

logic-high to enable REG1, REG2, and REG4. In

this case, the signal driving PWRHLD 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

timing and sequence. When using the application

circuits shown in Figure 2, the nIRQ signal is

asserted 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 PWRHLD

input, disabling the regulators and shutting the

system down.

nMSTR Enable Input

In most applications, connect nMSTR to an active

low, momentary push-button switch to utilize the

Innovative PowerTM

ActivePMUTM is a trademark of Active-Semi.

I2CTM is a trademark of Philips Electronics.

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www.active-semi.com

Copyright © 2009 Active-Semi, Inc.

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