8

Reverse polarity protection

Reverse polarity protection can be implemented on board using two different solutions (or both, which is

recommended):

1.

Placing a resistor (RGND) between IC GND pin and load GND

2.

Placing a diode in parallel to a resistor between IC GND pin and load GND

If option 1 is selected, the minimum resistance value must be selected according to the following equation:

RGND≥ VCCIGNDCC

(1)

where

IGNDCCistheDCreversegroundpincurrentandcanbefoundinTable2.

The power dissipated by RGND during reverse polarity is:

PD= VCC2

RGND

(2)

If option 2 is selected, the diode has to be chosen by taking into account VRRM > |VCC| and its power dissipation

capability:

PD≥IS×VF

(3)

Note:

In normal operation (no reverse polarity), there is a voltage drop (ΔV) between GND of the device and GND of

the system. Using option 1, ΔV = Rgnd * Icc. Using option 2, ΔV = VF@(IF).

Figure 23. Reverse polarity protection

Note:

Input(i) is intended as any input pin on logic side.

This schematic can be used with any type of load.

ISO808A, ISO808A-1

Reverse

polarity protection

DS14170 - Rev 1

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