Application information VN610SP-E
18/27 Doc ID 10889 Rev 5
If the calculated power dissipation requires the use of a large resistor, or several devices
have to share the same resistor, then ST suggests using solution 2 below.
3.1.2 Solution 2: a 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 (j600mV) 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 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
maximum DC rating. The same applies if the device is subject to transients on the V
CC
line that are greater than those shown in the ISO T/R 7637/1 table.
3.3 MCU I/O protection
If a ground protection network is used and negative transients 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 µC I/O pins from latching 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
OHμC
- V
IH
- V
GND
) / I
IHmax
Example
For the following conditions:
V
CCpeak
= - 100V
I
latchup
≥ 20mA
V
OHμC
≥ 4.5V
5kΩ ≤ R
prot
≤ 65kΩ.
Recommended values are:
R
prot
= 10kΩ
