ST72325AR7-Auto datasheet(211/243 Pages) STMICROELECTRONICS

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ST72325xxx-Auto

Electrical characteristics

Doc ID 13770 Rev 3

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Figure 88.

RESET pin protection when LVD is enabled

Note:

- The reset network protects the device against parasitic resets.

- The output of the external reset circuit must have an open-drain output to drive the ST7

reset pad. Otherwise the device can be damaged when the ST7 generates an internal reset

(LVD or watchdog).

- Whether the reset source is internal or external, the user must ensure that the level on the

RESET pin can go below the VIL maximum level specified in Section 19.9.1 on page 210.

Otherwise the reset will not be taken into account internally.

- Because the reset circuit is designed to allow the internal RESET to be output in the

RESET pin, the user must ensure that the current sunk on the RESET pin is less than the

absolute maximum value specified for IINJ(RESET) in Section 19.2.2 on page 191.

When the LVD is enabled, it is recommended not to connect a pull-up resistor or capacitor. A

10nF pull-down capacitor is required to filter noise on the reset line.

In case a capacitive power supply is used, it is recommended to connect a 1M

 pull-down

resistor to the RESET pin to discharge any residual voltage induced by the capacitive effect

of the power supply (this will add 5µA to the power consumption of the MCU).

Tips when using the LVD:

A. Check that all recommendations related to reset circuit have been applied (see notes

above).

B. Check that the power supply is properly decoupled (100nF + 10µF close to the MCU).

Refer to AN1709 and AN2017. If this cannot be done, it is recommended to put a 100nF +

 pull-down on the RESET pin.

C. The capacitors connected on the RESET pin and also the power supply are key to avoid

any start-up marginality. In most cases, steps A and B above are sufficient for a robust

solution. Otherwise, replace 10nF pull-down on the RESET pin with a 5µF to 20µF

capacitor.

0.01µF

ST72XXX

PULSE

GENERATOR

Filter

RON

VDD

WATCHDOG

LVD RESET

INTERNAL

RESET

EXTERNAL

Required



Optional

(note 3)

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