Application information VND5025LAK-E
22/31 Doc ID 12794 Rev 6
If the calculated power dissipation leads to a large resistor or several devices have to share
the same resistor, then ST suggests to utilize the following Solution 2.
3.1.2 Solution 2: Diode (D
GND
) in the ground line
If the device drives an inductive load, insert a resistor (R
GND
=1kΩ) in parallel to D
GND
.
This small signal diode can be safely shared among several different HSDs. Also in this
case, the presence of the ground network produces a shift ( 600mV) in the input
threshold and in the status output values if the microprocessor ground is not common to the
device ground. This shift does not vary if more than one HSD shares the same
diode/resistor network.
3.2 Load dump protection
D
ld
is necessary (Voltage Transient Suppressor) if the load dump peak voltage exceeds the
V
CC
maximum DC rating. The same applies if the device is subject to transients on the V
CC
line that are greater than the ones shown in the ISO 7637-2:2004E table.
3.3 Microcontroller I/Os protection
If a ground protection network is used and negative transients are present on the V
CC
line,
the control pins are pulled negative. ST suggests to insert an in-line resistor (R
prot
) to
prevent the µC I/Os pins from latch-up.
The value of these resistors is a compromise between the leakage current of µC and the
current required by the HSD I/Os (input levels compatibility) with the latch-up limit of µC
I/Os.
-V
CCpeak
/I
latchup
≤ R
prot
≤ (V
OHµC
-V
IH
-V
GND
) / I
IHmax
Calculation example:
For V
CCpeak
= -100V and I
latchup
≥ 20mA; V
OHµC
≥ 4.5V
5k
Ω
≤ R
prot
≤ 65k
Ω
Recommended values: R
prot
=10k
Ω
, C
EXT
= 10nF
