VN31

6/13

Figure 7. Switching Time Waveforms

FUNCTIONAL DESCRIPTION

The device has a diagnostic output which

indicates open load conditions in off state as well

overtemperature. The truth table shows input,

diagnostic and output voltage level in normal

operation and in fault conditions. The output

signals are processed by internal logic. The open

load diagnostic output has a 5 ms filtering. The

filter gives a continuous signal for the fault

condition after an initial delay of about 5 ms. This

means

that

a

disconnection

during

normal

operation, with a duration of less than 5 ms does

not affect the status output. Equally, any re-

connection

of

less

than

5

ms

during

a

disconnection duration does not affect the status

output. No delay occur for the status to go low in

case of overtemperature conditions. From the

falling edge of the input signal the status output

initially low in fault condition (over temperature or

case of open load. These feature fully comply with

International Standard Office (I.S.O.) requirement

for automotive High Side Driver.

To protect the device against short circuit and over

current conditions, the thermal protection turns the

integrated Power MOS off at a minimum junction

temperature of 140 °C. When the temperature

returns to 125 °C the switch is automatically turned

on again. In short circuit the protection reacts with

virtually no delay, the sensor being located in the

region of the die where the heat is generated.

Driving inductive loads, an internal function of the

device ensures the fast demagnetization with a

This function allows to greatly reduce the power

dissipation according to the formula:

where f = switching frequency and

Based on this formula it is possible to know the

value of inductance and/or current to avoid a

thermal shut-down. The maximum inductance

which causes the chip temperature to reach the

shut down temperature in a specific thermal

environment, is infact a function of the load current

PROTECTING THE DEVICE AGAIST LOAD

DUMP - TEST PULSE 5

The device is able to withstand the test pulse No.

7637/1 without any external component. This

means that all functions of the device are

performed

as

designed

after

exposure

to

disturbance at level II. The VN31 is able to

withstand the test pulse No.5 at level III adding an

external resistor of 150 ohm between pin 1 and

ground plus a filter capacitor of 1000

µF between

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 10).

The consequences of the voltage drop across this

diode are as follows:

– If the input is pulled to power GND, a negative

respect to power GND).

– The undervoltage shutdown level is increased

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 application circuit in Figure 11), which

becomes the common signal GND for the whole

This solution allows the use of a standard diode.