Datasheet

Application information VND5T100AJ-E
22/32 Doc ID 018513 Rev 2
3.1.2 Solution 2: diode (D
GND
) in the ground line
A resistor (R
GND
=4.7kshould be inserted in parallel to D
GND
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 produces 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 not varies 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 to
V
CC
max 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 T/R 7637/2 table.
3.3 MCUI/Os protection
If a ground protection network is used and negative transient are present on the V
CC
line,
the control pins are pulled negative. ST suggests that a resistor (R
prot
) be inserted 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.
-V
CCpeak
/I
latchup
 R
prot
 (V
OHC
-V
IH
-V
GND
) / I
IHmax
Calculation example:
For V
CCpeak
= -600 V and I
latchup
 20 mA; V
OHC
 4.5 V
30 k  R
prot
 180 k.
Recommended R
prot
value is 60 k