Application information VN02N
12/16
3.1 Functional description
The device has a diagnostic output which indicates open circuit (no load) and over
temperature conditions. The output signals are processed by internal logic. To protect the
device against short circuit and over-current condition, the thermal protection turns the
integrated Power MOS off at a minimum junction temperature of 140°C. When the
temperature returns to about 125°C the switch is automatically turned on again. In short
circuit conditions the protection reacts with virtually no delay, the sensor being located in the
region of the die where the heat is generated.
3.2 Protecting the device against reverse battery
The simplest way to protect the device against a continuous reverse battery voltage (-26V)
is to insert a Schottky diode between pin 1 (GND) and ground, as shown in the typical
application circuit (Figure 12.).
The consequences of the voltage drop across this diode are as follows:
● If the input is pulled to power GND, a negative voltage of -VF is seen by the device. (VIL,
V
IH thresholds and VSTAT are increased by VF with respect to power GND).
● The undervoltage shutdown level is increased by VF.
If there is no need for the control unit to handle external analog signals referred to the power
GND, the best approach is to connect the reference potential of the control unit to node [1]
(see Figure 13.), which becomes the common signal GND for the whole control board. In
this way no shift of V
IH, VIL and VSTAT takes place and no negative voltage appears on the
INPUT pin; this solution allows the use of a standard diode, with a breakdown voltage able
to handle any ISO normalized negative pulses that occours in the automotive environment.
