ST72325AR7B3 datasheet(163/197 Pages) STMICROELECTRONICS

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ST72325xx

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CONTROL PIN CHARACTERISTICS (Cont’d)

Figure 87. RESET pin protection when LVD is enabled.1)2)3)4)

Figure 88. RESET pin protection when LVD is disabled.1)

Note 1:

– 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).

– Whatever the reset source is (internal or external), the user must ensure that the level on the RESET pin can go

below the VIL max. level specified in section 12.9.1 on page 162. 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 en-

sure that the current sunk on the RESET pin is less than the absolute maximum value specified for IINJ(RESET) in

section 12.2.2 on page 143.

Note 2: 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.

Note 3: In case a capacitive power supply is used, it is recommended to connect a 1M

Ωpull-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).

Note 4: Tips when using the LVD:

– 1. Check that all recommendations related to reset circuit have been applied (see notes above).

– 2. 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 + 1M

Ω pull-down on the RESET pin.

– 3. The capacitors connected on the RESET pin and also the power supply are key to avoid any start-up marginality.

In most cases, steps 1 and 2 above are sufficient for a robust solution. Otherwise: replace 10nF pull-down on the

RESET pin with a 5µF to 20µF capacitor.

0.01

μF

ST72XXX

PULSE

GENERATOR

Filter

RON

VDD

WATCHDOG

LVD RESET

INTERNAL

RESET

EXTERNAL

Required

Optional

(note 3)

0.01

μF

EXTERNAL

RESET

CIRCUIT

USER

Required

ST72XXX

PULSE

GENERATOR

Filter

RON

VDD

WATCHDOG

INTERNAL

RESET

ST72325AR7B3 Datasheet(PDF) 163 Page - STMicroelectronics

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