VN02ANSP datasheet(5/9 Pages) STMICROELECTRONICS

5 / 9 page

FUNCTIONAL DESCRIPTION

The device has a diagnostic output which

indicates over temperature conditions.

The truth table shows input, diagnostic output

status and

output voltage level in

normal

operation and fault conditions. The output signals

are processed by internal logic.

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

oC. When the

temperature returns to 125

oC the switch is

automatically turned on again. To ensure the

protection in all VCC conditions and in all the

junction temperature range it is necessary to limit

the voltage drop across Drain and Source (pin 3

and 5) at 28V according to:

Vds =VCC -IOV *(Ri +Rw +Rl)

where:

Ri = internal resistence of Power Supply

Rw = Wires resistance

Rl = Short Circuit resistance

Driving inductive loads, an internal function of the

device ensures the fast demagnetization with

typical voltage (Vdemag) of -18V.

This function allows the reduction of the power

dissipation according to the formula:

Pdem = 0.5 * Lload *(Iload)

2 * [(VCC +Vdem)/Vdem]* f

where f = Switching Frequency

Based on this formula it is possible to know the

value of inductance and/or current to avoid a

thermal shut-down.

PROTECTING THE DEVICE AGAINST RE-

VERSE BATTERY

The simpliest way to protect the device against a

continuous reverse battery voltage (-36V) is to

insert a Schottky diode between pin 1 (GND) and

ground, as shown in the typical application circuit

(Fig. 3). 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,Vih

thresholds and Vstat are increased by Vf with

respect to power GND).

The undervoltage shut-down 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 application circuit in fig. 4), which becomes

the common signal GND for the whole control

board avoiding shift of Vih,Vil and Vstat. This

solution allows the use of a standard diode.

Figure 2: Over Current Test Circuit

VN02ANSP

5/9

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