VN808-E datasheet(13/18 Pages) STMICROELECTRONICS

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VN808-E

Reverse polarity protection

13/18

Reverse polarity protection

A schematic solution to protect the IC against a reverse polarity condition is proposed.

This schematic is effective with any type of load connected to the outputs of the IC.

The RGND resistor value can be selected according to the following conditions to be met:

RGND ≤ 600 mV / (IS in ON state max).

RGND ≥ (-VCC) / (-IGND)

where -IGND is the DC reverse ground pin current and can be found in the absolute

maximum rating section of the device datasheet.

The power dissipation associated to RGNG during reverse polarity condition is:

PD = (-VCC)

2/R

GND

This resistor can be shared by several different ICs. In such case IS value on formula (1) is

the sum of the maximum ON-state currents of the different devices.

Please note that if the microprocessor ground and the device ground are separated then the

voltage drop across the RGND (given by IS in ON state max * RGND) produce a difference

between the generated input level and the IC input signal level. This voltage drop will vary

depending on how many devices are ON in the case of several high side switches sharing

the same RGND.

Figure 9.

Reverse polarity protection

Status

Input

GND

Output

+ Vcc

GND

(Optional)

Load

Status

Input

GND

Output

+ Vcc

GND

(Optional)

Load

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