8/23
VN920 / VN920-B5 / VN920SO
GND PROTECTION NETWORK AGAINST
REVERSE BATTERY
Solution 1: Resistor in the ground line (R
GND
only). This
can be used with any type of load.
The following is an indication on how to dimension the
R
GND
resistor.
1) R
GND
≤ 600mV / (I
S(on)max
).
2) R
GND
≥ (−V
CC
) / (-I
GND
)
where -I
GND
is the DC reverse ground pin current and can
be found in the absolute maximum rating section of the
device’s datasheet.
Power Dissipation in R
GND
(when V
CC
<0: during reverse
battery situations) is:
P
D
= (-V
CC
)
2
/R
GND
This resistor can be shared amongst several different
HSD. Please note that the value of this resistor should be
calculated with formula (1) where I
S(on)max
becomes the
sum of the maximum on-state currents of the different
devices.
Please note that if the microprocessor ground is not
common with the device ground then the R
GND
will
produce a shift (I
S(on)max
* R
GND
) in the input thresholds
and the status output values. This shift will vary
depending on how many devices are ON in the case of
several high side drivers sharing the same R
GND
.
If the calculated power dissipation leads to a large resistor
or several devices have to share the same resistor then
the ST suggests to utilize Solution 2 (see below).
Solution 2:
A diode (D
GND
) in the ground line.
A resistor (R
GND
=1kΩ) should be inserted in parallel to
D
GND
if the device will be driving an inductive load.
This small signal diode can be safely shared amongst
several different HSD. Also in this case, the presence of
the ground network will produce a shift (
600mV) in the
input threshold and the status output values if the
microprocessor ground is not common with the device
ground. This shift will not vary if more than one HSD
shares the same diode/resistor network.
LOAD DUMP PROTECTION
D
ld
is necessary (Voltage Transient Suppressor) if the
load dump peak voltage exceeds V
CC
max DC rating. The
same applies if the device will be subject to transients on
the V
CC
line that are greater than the ones shown in the
ISO T/R 7637/1 table.
µ
C I/Os PROTECTION:
If a ground protection network is used and negative
transients are present on the V
CC
line, the control pins will
be pulled negative. ST suggests to insert a resistor (R
prot
)
in line to prevent the µC I/Os pins to 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
5kΩ ≤ R
prot
≤ 65kΩ.
Recommended R
prot
value is 10kΩ.
1
APPLICATION SCHEMATIC
V
CC
GND
OUTPUT
D
GND
R
GND
D
ld
µ
C
+5V
R
prot
V
GND
INPUT
CURRENT SENSE
R
SENSE
R
prot
