ACT5880 datasheet(61/87 Pages) ACTIVE-SEMI

61 / 87 page

ACT5880

Rev 2, 03-Sep-13

- 61 -

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Push-button Inputs

The nPBIN features dual-functions input, by

detecting if it is directly shorted to ground or pulled

to ground through a resistor of around 50kΩ (good

in range of 24kΩ to 82kΩ). See the Figure 2 for the

external connection, the push-button that directly

grounds the nPBIN input is namely the "Reset Key",

is identified as a manual reset request by the

ACT5880 when it is pressed; The other push-button

is namely the "Enable Key", is identified as a device

enable request when it is pressed.

When either "Reset Key" or "Enable Key" is

pressed, the nPBSTAT asserts low; In both cases

the ACT5880 may assert interrupt to the application

system if it is programmed so, by pulling the nIRQ

low.

Figure 2:

The External Circuit for The Push button Input

nPBSTAT Output

nPBSTAT is an open-drain output that reflects the

state of the nPBIN input; nPBSTAT is asserted low

whenever nPBIN is asserted, and is high-Z

otherwise. This output is typically used as an push

button status signal to the processor, to initiate a

software-programmable routine such as operating

mode selection or to open a menu. Connect

nPBSTAT to an appropriate supply voltage

(typically IO voltage) through a 10kΩ or greater

resistor.

Control Sequences

Power Output Sequence

A typical enable sequence initiates as a result of

pressing “Enable Key”, which is one of the 5 events

mentioned in the "Device Power States", and it

turns ACT5880 into the power-on default state or

last powered state before being turned off by

removing all the 5 events. When REG1 reaches its

power-OK threshold, nRSTO is asserted low. If

REG1 is above its power-OK threshold when the

reset timer expires, nRSTO is de-asserted. If the

equipment system pulls the PWRHLD (or any of the

HFPWR, ACOK or RTC alarm wake-up) to a logic

high before the push-button is released, the enable

state of the ACT5880 is kept. If this does not

happen, the ACT5880 goes back to the disable

state. The Figure 3 shows the states of the

ACT5880 and its power rails. The ACT5880 has 2

programmable reset timeout, which is optional on

default setting and programmable in operation.

When "Enable Key" is pressed in ACT5880 enable

state, the response depends on if the OUT1 outputs

is normal at the moment.

Figure 3:

Power Rail Sequence

When OUT1 is already enabled, the push button

event only asserts nPBSTAT (and the nIRQ if it is

programmed so). When the OUT1 is disabled, the

push button event starts OUT1 and pulls the nRSTO

low until the reset time-out expires after the OUT1 is

in regulation, also asserts nPBSTAT (and nIRQ if it is

programmed so), while no change to other

rails.Figure 4 shows the "Enable Key" push button

event when OUT1 is disabled.

Figure 4:

REG1 to nRSTO Sequence

See Figure 4 for illustration of pressing of "Enable

Key" when OUT1 does not output. When OUT1 is in

ACT5880

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