7/21
VN800S / VN800PT
GND PROTECTION NETWORK AGAINST
REVERSE BATTERY
Soluti on 1: Resistor in the ground line (R
GND
only). This
can be us ed with any t ype of load .
The fo llow ing is an indica tion on how to di mension the
R
GND
resistor.
1) R
GND
≤ 600mV / (I
S(on)ma x
).
2) R
GND
≥ (−VCC) / (-I
GND
)
where -I
GND
is the DC re vers e grou nd pi n cu rren t an d can
be found in the absolute maximum rating section of the
device’s datasheet.
Power Dissipation in R
GND
(when VCC<0: during reverse
battery situations) is:
P
D
= (-VCC)2/R
GND
This resistor can be shared amongst several different
HSD. Please note tha t t h e va l u e of this resis t o r sh ould be
calcul ated with form ula (1) wher e I
S(on)max
becomes t he
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 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 hav e to share the sa me resisto r then
the ST suggests to utiliz e Solu tio n 2 (se e below ).
Solution 2:
A diode (D
GND
) in the gro und line.
A resistor (R
GND
=1kΩ) should be inserted in parallel to
D
GND
if the devi ce will be driving an inducti ve load.
This small signal diode can be safely shared amongst
several different HSD. Also in this case, the presence of
the ground network wi ll produce a shift (
j
600mV) in t he
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 net work.
µC I/Os PROTECTION:
If a ground protection network is used and negative
transients are present on the V
CC
line, th e con trol p ins will
be pulled negative. ST suggests to insert a resistor (R
prot
)
in lin e to prevent the µC I/Os pins to latch-up.
The value of these resistors is a compromise between the
leakage c urrent of µC an d the current required by the
HSD I/Os ( Input le vels comp atibilit y) wi th the lat ch-up li mit
of µC I/Os.
-V
CCpeak/Ilatchup
≤ R
prot
≤ (V
OHµC-VIH-VGND
) / I
IHmax
Calculation example:
For V
CCpeak
= - 100V an d I
latchup
≥ 20mA; V
OHµC
≥ 4.5V
5kΩ ≤ R
prot
≤ 65kΩ.
Recommended R
prot
value is 10kΩ.
APPLICATION SCHEMATIC
V
CC
INPUTn
GND
STATUSn
OUTPUTn
Volt.
Reg
BUS
ASIC
Control & Diagnostic I/O
5V
24VDC
V
CC
DGND
VGND
RGND
Rprot
Rprot
LOAD
R
L