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VB027 / VB027(011Y) / VB027(012Y)
1
PRINCIPLE OF OPERATION
The
VB027, VB027(011Y), VB027(012Y) 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 VB027, VB027(011Y),
VB027(012Y) 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 VB027,
VB027(011Y), VB027(012Y) 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 currentswitch-off, the
primary voltage HV
C
is clamped by a series of Zener
diodes at an internally set value V
cl
, typically 360V.
The collector current sensed throughthe R
sense
, is limited
thanks to the “Current limiter” block that, as soon as theI
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.
VB027,
VB027(011Y), VB027(012Y)
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.
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:
I
C(DIAG1)
info after x ms (I
C(DIAG1)
=2.5A)
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
1.5A and, in this example, the switch-off current will be
kx*1.5 / 2.5.
OVERVOLTAGE
The
VB027, VB027(011Y), VB027(012Y) 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)
FIGURE 1: Application circuit
