Application information VN800PS-E
16/27 Doc ID 15610 Rev 4
If the calculated power dissipation leads to a large resistor or several devices have to share
the same resistor then the ST suggests to utilize Solution 2 (see Section 3.1.2).
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 is 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 produces a shift (≈600 mV) in the input threshold
and the status output values if the microprocessor ground is not common with the device
ground. This shift not varies 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 Microcontroller I/Os protection
If a ground protection network is used and negative transients 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 microcontroller I/Os 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
OHµC
-V
IH
-V
GND
) / I
IHmax
Calculation example:
For V
CCpeak
= -100 V and I
latchup
≥ 20 mA; V
OHµC
≥ 4.5 V
5k Ω ≤ R
prot
≤ 65 kΩ.
Recommended R
prot
value is 10 kΩ.
