8/23
VN920 / VN920-B5 / VN920SO
GND PROTECTION NETWORK AGAINST
REVERSE BATTERY
Soluti on 1: Resistor in the ground line (R
GND
only). This
can be us ed with any type of load.
The fo llowin g is an indica tion on how to dim ension 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 that the val u e of this resi s to r sh ou l d 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
depend ing on how many devi ces are ON in the c ase 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 gr ound line.
A resistor (R
GND
=1kΩ) sh ould b e insert ed in paral lel 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 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 diod e/resisto r network.
LOAD DUMP PROTECTION
Dld is necessary (Voltage Transient Suppressor) if the
load dump peak voltage exceeds VCC max DC rating. The
same applies if the device will be subject to transients on
the VCC line that are grea ter tha n the ones sh own 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 VCC 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.
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