Application information

VND920

18/26

Doc ID 7767 Rev 6

3.1.2

Solution 2: diode (DGND) in the ground line

A resistor (RGND = 1 kΩ) should be inserted in parallel to DGND if the device drives an

inductive load.

This small signal diode can be safely shared amongst several different HSDs. Also in this

case, the presence of the ground network will produce a shift (

≈600 mV) in the input

threshold and in the status output values if the microprocessor ground is not common to the

device ground. This shift will not vary if more than one HSD shares the same diode/resistor

network.

Series resistor in INPUT and STATUS lines are also required to prevent that, during battery

voltage transient, the current exceeds the absolute maximum rating.

Safest configuration for unused INPUT and STATUS pin is to leave them unconnected.

3.2

Load dump protection

Dld is necessary (Voltage Transient Suppressor) if the load dump peak voltage exceeds the

VCC max DC rating. The same applies if the device is subject to transients on the VCC line

that are greater than the ones shown in the ISO 7637-2: 2004(E) table.

3.3

MCU I/Os protection

If a ground protection network is used and negative transient are present on the VCC line,

the control pins will be pulled negative. ST suggests to insert a resistor (Rprot) in line to

prevent the microcontroller I/O pins to latch-up.

The value of these resistors is a compromise between the leakage current of microcontroller

and the current required by the HSD I/Os (Input levels compatibility) with the latch-up limit of

microcontroller I/Os.

-VCCpeak/Ilatchup ≤ Rprot ≤ (VOHµC -VIH -VGND) / IIHmax

Calculation example:

For VCCpeak = -100V and Ilatchup ≥ 20 mA; VOHµC ≥ 4.5 V

5k

Ω ≤ Rprot ≤ 65 kΩ.

Recommended values: Rprot =10kΩ .

Obsolete

Product(s)

- Obsolete

Product(s)