Application information VN800S / VN800PT
16/32
3.1.2 Solution 2: diode (D
GND
) in the ground line
A resistor (R
GND
= 1kΩ) 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 will produce 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 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.
3.2 MCU 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
OH
µ
C
-V
IH
-V
GND
) / I
IHmax
Calculation example:
For V
CCpeak
= - 100V and I
latchup
≥ 20mA; V
OH
µ
C
≥ 4.5V
5kΩ ≤ R
prot
≤ 65kΩ.
Recommended values: R
prot
=10kΩ .
