VB027ASP Datasheet, PDF (4/8 Pages) STMicroelectronics – HIGH VOLTAGE IGNITION COIL DRIVER POWER IC

VB027ASP
PRINCIPLE OF OPERATION
The VB027ASP is mainly intended as a high
voltage power switch device driven by a logic
level input and interfaces directly to a high energy
electronic ignition coil.
The input Vin of the VB027ASP is fed from a low
power signal generated by an external controller
that determines both dwell time and ignition point.
During Vin high (≥ 4V) the VB027ASP increases
current in the coil to the desired, internally set
current level.
After reaching this level, the coil current remains
constant until the ignition point, that corresponds
to the transition of Vin from high to low (typ. 1.9V
threshold).
During the coil current switch-off, the primary
voltage HVc is clamped at an internally set value
Vcl, typically 345V.
The transition from saturation to desaturation,coil
current limiting phase, must have the ability to
accomodate an overvoltage. A maximum
overshoot of 20V is allowed.
THERMAL BEHAVIOUR
You can see in the block diagram of the
VB027ASP a box called overtemperature
protection. The purpose of this circuit is to shift
the current level at witch the 1st diagnostic is
activated down of about 2.5A.
This information can be managed by the micro
that can take the corrective actions in order to
reduce the power dissipation.
This block is not an effective protection but just
an overtemperature detection. The shift down of
the 1st flag level cannot be present for
temperatures lower than 125 ^oC.
As an example of its behaviour 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 1st flag threshold.
EXAMPLE:
Iflag info after X msec. (Iflag = 4.5A)
Iswitch off after K*X msec.
As soon as the temperature rises over the
overtemp. threshold, the 1st diagnostic is shifted
down to about 2.5A and in this example, the
switch off current will be K*X*2.5/4.5 helping the
system to reduce the power dissipation.
As you can see this behaviour is not a protection
but just a feedback for the micro.
FEEDBACK
When the collector current exceeds 4.5A, the
feedback signal is turned high and it remains so,
until the load current reaches 5.8A (second
threshold), at that value, the feedback signal is
turned low.
OVERVOLTAGE
The VB027BSP can withstand the following
transients of the battery line:
-100V/2msec (Ri = 10 Ω)
+100V/0.2msec (Ri = 10 Ω)
+50V/400msec (Ri = 4.2 Ω, with VIN = 3 V)
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