VN750PS-E Electrical specifications
Doc ID 16782 Rev 3 17/27
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.
2.6 Load dump protection
D
ld
is necessary (voltage transient suppressor) if the load dump peak voltage exceeds the
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 7637-2: 2004(E) table.
2.7 Microcontroller 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 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
µ
C
-V
IH
-V
GND
) / I
IHmax
Calculation example:
For V
CCpeak
= - 100 V and I
latchup
≥ 20 mA; V
OH
µ
C
≥ 4.5 V
5kΩ ≤ R
prot
≤ 65 kΩ.
Recommended values: R
prot
=10kΩ.
2.8 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.
