VB027BSP Datasheet, PDF (4/7 Pages) STMicroelectronics – HIGH VOLTAGE IGNITION COIL DRIVER POWER I.C.

VB027BSP
PRINCIPLE OF OPERATION
The VB027BSP 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.
The input V_IN of the VB027BSP is fed from a low power
signal generated by an external controller that determines
both dwell time and ignition point. During V_IN high (≥4V)
the VB027BSP increases current in the 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
V_IN to the low state. During the coil current switch-off, the
primary voltage HV_C is clamped by a series of Zener
diodes at an internally set value V_cl typically 365V.
The collector current sensed through the R_sense, is limited
thanks to the “Current limiter” block that, as soon as the I_cl
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
output pin (HV_C) is pulled below ground by a negative
current due to leakage inductances and stray
capacitances of the ignition coil. This can cause parasitic
glitches on the diagnostic output. VB027BSP 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.
FIGURE 1: Application circuit
THERMAL BEHAVIOUR
You can see in the block diagram of the VB027BSP a box
called overtemperature protection. The purpose of this
circuit is to shift the current level at which the first
diagnostic is activated down to about 2.5A.
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:
I_C(DIAG1) info after x ms (I_C(DIAG1)=4.5A)
I_switch-off info after kx ms.
As soon as the temperature rises over the overtemp
threshold, the first diagnostic is shifted down to about
2.5A and, in this example, the switch-off current will be
kx*2.5 / 4.5.
OVERVOLTAGE
The VB027BSP can withstand the following transients of
the battery line:
-100V / 2ms (R_i=10Ω)
+100V / 0.2ms (R_i=10Ω)
+50V / 400ms (R_i=4.2 Ω, with V_IN=3V)
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