STV0974 datasheet(31/69 Pages) STMICROELECTRONICS

31 / 69 page

Functional description

STV0974

31/61

4.7

Power management unit

The STV0974 is reset via the internal PowerOnReset cell (POR) or via an external control reset

line. The device reset is controlled by the RST pin.

The POR cell generates an output signal on the POR pin every time that the device external supply

is switched off or the PDN pin is activated.

The STV0974 enters into power-up phase in two circumstances:

● when the supplies are turned on with PDN pin high.

● when the STV0974 exits from power-down (PDN pin rises with supplies already on).

At power-up, the STV0974 performs its initialization phase and goes into sleep mode.

Figure 18: Reset of

STV0974

Figure 19: State machine at power-up

STV0974

POR

RST

Host control line

(left unconnected)

Application with external reset line

STV0974

POR

RST

Application with POR reset cell

Connection

on application

board

Supplies Off

Vdd = 0

Boot

Power-down

Supplies

turned-on

PDN low

PDN high

Sleep mode

Supplies

turned-off

& PDN high

Supplies turned on & PDN low

Supplies

turned-off

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