Datasheet

VN750-E Electrical specifications
Doc ID 10891 Rev 7 17/38
2.5.2 Solution 2: diode (D
GND
) in the ground line
A resistor (R
GND
=1 kΩ) should be inserted in parallel to D
GND
if the device drives an
inductive load.
This small signal diode can be safely shared amongst several different HSDs. Also in this
case, the presence of the ground network produces a shift (≈600mV) in the input threshold
and in the status output values if the microprocessor ground is not common to the device
ground. This shift does 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.
The 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 are 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 from latching-up limit of µC
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
=10 kΩ.
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 +5 V 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)
.