ST7LITE49M datasheet(171/188 Pages) STMICROELECTRONICS

171 / 188 page

ST7LITE49M

Electrical characteristics

171/188

Figure 96.

RESET pin protection when LVD is enabled3)4)

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 13.10.1 on page 170.

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 Table 66. on page 144.

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

Ω 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

●

Check that all recommendations related to ICCCLK and reset circuit have been applied

(see caution in Table 2 on page 16 and notes above).

●

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.

●

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

ST7xxx

PULSE

GENERATOR

Filter

RON

VDD

INTERNAL

RESET

EXTERNAL

Required

Ω

Optional

(note 3)

WATCHDOG

LVD RESET

ILLEGAL OPCODE 5)

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