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VB027 / VB027(011Y) / VB027(012Y)

1

PRINCIPLE OF OPERATION

The

intended as high voltage power switch device driven by a

logic level input and interfaces directly to a high energy

electronic ignition coil.

The

input

VB027(011Y),

by an external controller that determines both dwell time

coil to the desired, internally set current level.

When the collector current exceeds 4.5A, the diagnostic

signal is turned high and it remains so, until the load

current reaches 5.8A (second threshold). At that value,

the diagnostic signal is turned low, and the

µC forces the

level is reached, forces the darlington (using the “Driver”

block) to limit the current provided.

The transition from saturation to desaturation, coil current

limiting phase, must have the ability to accommodate an

overvoltage. A maximum overshoot of 20V is allowed.

There can be some short period of time in which the

current

due

to

leakage

inductances

and

stray

capacitances of the ignition coil. This can cause parasitic

glitches

on

the

diagnostic

output.

VB027,

circuit that allows to lock the p-buried layer potential of the

linear stage to the collector power, when the last one is

pulled underground.

THERMAL BEHAVIOUR

You can see in the block diagram of the

VB027,

VB027(011Y),

VB027(012Y)

a

box

called

overtemperature protection. The purpose of this circuit is

to shift the current level at which the first diagnostic is

activated down of about 1A.

This information can be managed by the micro that can

take the corrective action in order to reduce the power

dissipation. This block is not an effective protection but

just an overtemperature detection. The shift down of the

first flag level cannot be present for temperatures lower

than 125

°C.

As an example of its behavior you can suppose a very

simple motor management system in which the micro

does just a simple arithmetic calculation to decide when to

switch-off the device after the first flag threshold.

EXAMPLE:

As soon as the temperature rises over the overtemp

threshold, the first diagnostic is shifted down to about

1.5A and, in this example, the switch-off current will be

kx*1.5 / 2.5.

OVERVOLTAGE

The

VB027,

VB027(011Y),

withstand the following transients of the battery line:

FIGURE 1: Application circuit