Datasheet

Application information VN920SP-E
18/27 Doc ID 10896 Rev 4
3.1.2 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.
Safest configuration for unused INPUT and STATUS pin is to leave them unconnected, while
unused SENSE pin has to be connected to ground pin.
3.2 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 Table 12.
3.3 MCU I/Os protection
If a ground protection network is used and negative transient are present on the V
CC
line,
the control pins is 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
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.