VND05BSP datasheet(5/9 Pages) STMICROELECTRONICS

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FUNCTIONAL DESCRIPTION

The device has a diagnostic output which

indicates open load in on-state, open load in

off-state,

over

temperature

conditions

and

stuck-on to VCC.

From the falling edge of the input signal, the

status output, initially low

to signal a fault

condition

(overtemperature

open

load

on-state), will go back to a high state with a

different delay in case of overtemperature (tpovl)

and in case of open open load (tpol) respectively.

This feature allows to discriminate the nature of

the detected fault. 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

oC. When this temperature returns to 125 oC

the switch is automatically turned on again. In

short circuit the protection reacts with virtually no

delay, the sensor being located inside the Power

MOS area. An internal function of the devices

ensures the fast demagnetization of inductive

loads with a typical voltage (Vdemag) of -18V. This

function allows to greatly reduces the power

dissipation according to the formula:

Pdem = 0.5

• Lload •(Ιload)2 • [(VCC+Vdemag)/Vdemag]

• f

where f = switching frequency and

Vdemag = demagnetization voltage.

The maximum inductance which causes the chip

temperature to reach the shut-down temperature

in a specified thermal environment is a function of

the load current for a fixed VCC, Vdemag and f

according to the above formula. In this device if

the GND pin is disconnected, with VCC not

exceeding 16V, it will switch off.

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

(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 shutdown level is increa-

sed

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. 3), 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.

Switching Time Waveforms

VND05BSP

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