UM1693 datasheet(28/196 Pages) STMICROELECTRONICS

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Reverse battery protection

UM1693

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DocID025505 Rev 1

clamped to minus one diode voltage due to the forward biased substrate diode of the HSD.

The N-channel MOSFET is turned off once the GND voltage begins to drop. This happens

within a few microseconds. The first current spike is due to the recharging of the VCC

capacitor. As soon as the GND voltage drops to -100 V, the N-channel MOSFET starts to

conduct in avalanche until the pulse amplitude drops below its breakdown voltage

BVDSS = 100 V.

The breakdown voltage BVDSS of the N-channel MOSFET either should be higher than the

maximum negative transient peak voltage of ISO 7637:2-2011(E) or the energy capability of

the N-channel MOSFET in avalanche must be high enough to sustain the transient pulse

energy.

Figure 10. Reverse battery test VN7016AJ-E (13.5 V

→ -4 V, 82 mΩ, R2 = 15 kΩ) as per

LV 124: 2009-10 standard

Figure 10 shows an example of an abrupt reverse battery test changing the polarity of the

battery supply from 13.5 V to -4 V within a few µs. The test setup used a 100 V/100 m

Ω

N-channel MOSFET with a gate resistor R2 = 15 k

Ω. The total line impedance is measured

with 82 m

Ω in line with the requirements of LV 124: 2009-10.

The N-channel MOSFET is able to turn-off within 10 µs about. During this time a relatively

high current will flow through the HSD substrate diode. The total energy dissipated in the

HSD is around 100 µJ, which is withstood by the M0-7 high-side driver family.

2.2.4

P-channel MOSFET in the VCC line

The P-channel MOSFET is connected in such a way that its Gate is connected to GND via a

resistor R2 and its drain to VCC pin, while the source acts as the reverse polarity protected

supply. In Figure 11 is reported a generic schematic with P-channel MOSFET configuration.

Compared to an N-channel MOSFET the device will be turned on by applying a negative

gate source voltage.

It is important to insert the transistor in the right direction, because the P-channel MOSFET

has as well an intrinsic anti parallel body diode which is in forward direction from drain to

source.

By referring the gate signal to the ground line, the device is fully turned on when the battery

is applied in the right polarity.

R2 = 15k

VCC - GND stress: ~0.1mJ

UM1693 Datasheet(PDF) 28 Page - STMicroelectronics