VNQ810-E
10/20
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.
Series resistor in INPUT and STATUS lines are also
required to prevent that, during battery voltage transient,
the current exceeds the Absolute Maximum Rating.
Safest configuration for unused INPUT and STATUS pin
is to leave them unconnected.
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.
.
µC I/Os PROTECTION:
If a ground protection network is used and negative
transient 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.
OPEN LOAD DETECTION IN OFF STATE
Off state open load detection requires an external pull-up
resistor (R
PU
) connected between OUTPUT pin and a
positive supply voltage (V
PU
) like the +5V line used to
supply the microprocessor.
The external resistor has to be selected according to the
following requirements:
1) no false open load indication when load is connected:
in this case we have to avoid V
OUT
to be higher than
V
Olmin
; this results in the following condition
V
OUT
=(V
PU
/(R
L
+R
PU
))R
L
<V
Olmin
2) no misdetection when load is disconnected: in this
case the V
OUT
has to be higher than V
OLmax
; this
results in the following condition R
PU
<(V
PU–
V
OLmax
)/
I
L(off2)
.
Because I
s(OFF)
may significantly increase if V
out
is
pulled high (up to several mA), the pull-up resistor R
PU
should be connected to a supply that is switched OFF
when the module is in standby.
The values of V
OLmin
, V
OLmax
and I
L(off2)
are available in
the Electrical Characteristics section.
Figure 9. Open Load detection in off state
VOL
V batt. VPU
R
PU
RL
R
DRIVER
+
LOGIC
+
-
INPUT
STATUS
V
CC
OUT
GROUND
I
L(off2)
Obsolete Product(s) - Obsolete Product(s)
