ACT8945A datasheet(28/42 Pages) ACTIVE-SEMI

28 / 42 page

ACT8945A

Rev 2, 11-Feb-14

- 28 -

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PWRHLD) before nPBIN is de-asserted. If the

microprocessor is unable to complete its power-up

routine successfully before the user releases the

push-button, the ACT8945A automatically shuts the

system down. This provides protection against

accidental or momentary assertions of the push-

button. If desired, longer “push-and-hold” times can

be implemented by simply adding an additional time

delay before asserting PWRHLD.

Control Sequences

The ACT8945A features a variety of control

sequences that are optimized for supporting system

enable and disable sequences of Atmel SAMA5D3

series and SAM9 series application processors.

Enabling/Disabling Sequence

ACT8945AQJ303 Sequence

A typical enable sequence is initiated whenever

nPBIN is asserted low via 50KΩ resistance. The

enable sequence begins by enabling REG3. When

REG3 reaches its power-OK threshold, nRSTO is

asserted low, resetting the microprocessor. When

REG3 reaches its power-OK threshold for 2ms ,

REG1 is enabled. When REG3 reaches its power-

OK threshold for 4ms , REG2 is enabled. When

REG3 is above its power-OK threshold when the

reset timer expires, nRSTO is de-asserted, allowing

the microprocessor to begin its boot sequence.

REG4, REG5, REG6 and REG7 can be enabled or

disabled by PWREN after system powers up.

During the boot sequence, the microprocessor must

assert PWRHLD, holding the regulators to ensure

that the system remains powered after nPBIN is

released.

As with the enable sequence, a typical disable

sequence is initiated when the user presses the

push-button, which interrupts the processor via the

nPBSTAT output. The actual disable sequence is

completely

software-controlled,

but

typically

involved initiating various “clean-up” processes

before finally set MSTROFF[ ] bit to 1 to shut the

system down.

: Typical value shown, actual delay time may vary from (T-1ms) x 88% to T x 112%, where T is the typical delay time setting.

Figure 3:

ACT8945AQJ303 Enable/Disable Sequence

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