L9788 datasheet(31/264 Pages) STMICROELECTRONICS

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DS12308 Rev 4

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L9788

Operation behavior

263

3.1.7

Power up from WAKE_UP_TIMER

The chip is powered up when an end counting is reached inside the wake_up_timer block.

The end and enable counting are set by MSC before the chip is powered down. In case the

power up of the chip is not completed in a MRD_EN_TIMEOUT from WAKE_UP_EOT end

of counting detection the Main Relay Driver is switched off and the chip goes in OFF state.

When U chip is already in on state (the logic is out of power on reset), the wake_up_timer

end counting only sets a flag, with no impact on power supply. This flag is named

WAKE_UP_EOT_DET (detection of a wake_up end of time condition) and is clear by

VDD5/VDDIO under voltage or by the MSC command WAKE_UP_EOT_RST. If no other

power on source is active a power down sequence is started.

The Main Relay Driver is not switched on by WAKE_UP_EOT if the device is powered in

permanent battery.

The MSC sets the programmable time on Wake up timer_SET Registers (CONFIG-REG15-

0 to CONFIG_REG15-2). The counting can be started/stopped by MSC command -

CONFIG_REG1[6:7] = WAKE_UP_TIMER_START_STOP[0:1] (CONFIG_REG1 D6;D7) -

or by switching the pin KEY_IN according to a selection set by MSC bit -

CONFIG_REG20[2] = WAKE_UP_TIMER_EN_SEL.

The counter counts time on the WAKE_UP_TIMER_CNT Register.

WAKE_UP_TIMER_CNT Register and Wake up timer_SET Register are being compared,

and when they match, WAKE_UP_EOT_DET signal will be set to high level to trigger a

power up sequence.

Condition:

4.8 V ≤ VB_IN ≤ 18 V, 3.5 V ≤ VB_STBY ≤ 18 V Tj -40 to 175 °C unless otherwise specified;

VB_STBY > 3.5 V, EOT can keep the counter value (allow to stop counting),



5 V < VB_STBY < 18 V, EOT full function, full parameter.

Iinput

Input current of

WK_IN

WK_IN ≤ 5 V

340

µA

WK_IN

WK_Tfilter

Filter time for

switching on/off

Guaranteed by test

scan

WK_IN

RPD

Pull-down resistor

WK_IN=1V

170

300

500

kΩ

WK_IN

MRD_EN_TIMEOUT

Timeout for power up

execution

331

500

650

WK_IN

Tbattery_det

Main logic POR

timeout (used to

recognize permanent

battery condition)

210

450

µs

Table 10. WK pins electrical characteristics (continued)

Symbol

Parameter

Test condition

Min

Typ

Max

Unit

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