L9788 datasheet(42/264 Pages) STMICROELECTRONICS

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Operation behavior

L9788

42/264

DS12308 Rev 4

3.4

Smart reset circuit

There are two Reset pins:

RSTN: reset pin linked to VDD5 supply;

RSTC: reset pin linked to VDDIO supply.

3.4.1

Smart reset RSTN pin

The RSTN pin is an input/output active low. As output pin the Smart Reset circuit takes into

account several events in the device in order to generate the proper reset signal at RSTN

pin for the microcontroller and for portion of the internal logic as well.

The RSTN in output (RSTN(OUT) is activated by the contributions described by the reset

matrix and is intended as reset for the external microcontroller.

The RSTN in input (RSTN(IN)) is filtered Trst_flt_RST and stops the internal logic as

described in the reset matrix.

The internal RSTN(OUT) has higher priority respect to the external RSTN(IN). The

RSTN(IN) is masked until Tmsk_RSTN after RSTN(OUT) has been released.

RSTN(OUT) and RSTN(IN) are recombined on the pad according to the scheme.

Figure 14. Reset circuit

The RSTN activates on the contributions specified by the reset matrix:

Figure 15. Reset matrix

GADG2511160825PS

RSTN(OUT)

RSTN(IN)

RSTN pin

100μs

GADG2511161010PS

VDDIO

RSTC

LOGIC

VDDIO uv = 0 pull up connected

VDDIO uv = 1 pull up disconnected

VDDIO uv = 0 LS OFF

VDDIO uv = 1 LS ON

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