VB027SP-E

Application information

Doc ID 018828 Rev 1

9/14

3

Application information

3.1

Principle of operation

The VB027SP-E is mainly intended as high voltage power switch device driven by a logic

level input and interfaces directly to a high energy electronic ignition coil.

VB027SP-E increases current in the coil to the desired, internally set current level.

When the collector current exceeds 4.5 A, the diagnostic signal is turned high and it remains

so, until the load current reaches 5.8 A (second threshold). At that value, the diagnostic

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 20 V is allowed. There can

negative current due to leakage inductances and stray capacitances of the ignition coil. This

can cause parasitic glitches on the diagnostic output. VB027SP-E has a built-in protection

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.

3.2

Thermal behaviour

You can see in the block diagram of the VB027SP-E (see Figure 1) 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 1 A.

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 overtemperature threshold, the first diagnostic is

shifted down to about 1.5 A and, in this example, the switch-off current is kx * 1.5 / 2.5.