trol market provides integrated open-load de-
tection that is specific to any of the individual
channels. As with the overload detection, this
greatly helps OEMs to reduce the time to iden-
tify the root cause of such a failure.
Open load when driver is still off [OLI]: Even
before the switch is turned on, an open load
(wire-break) can be detected. This is possible
because in addition to monitoring the output
current, the voltage at the output of the IC is
also being monitored. In case of the output
being in off-state a small trickle current of 25µA
is passed through the load. For loads with an
ohmic resistance of less than 12kohm, if the
output is disconnected from the load, the output
will float at a voltage higher than 2V which in
turn triggers the OLI diagnostic feedback.
Short to Vbb while the output is off [SCV]:
The switch output could erroneously be con-
nected to Vbb. Root causes may include wiring
error, a short circuit during operation, or a
natural disaster which leaves the equipment
flooded. This condition can also be detected
by the IC.
Overtemperature at an output [OTA]: Excessive
heavy duty operation of outputs may be an in-
dication of gradual degradation of the ma-
chinery on the factory floor. For this reason
each of the output channels is equipped with
an individual temperature sensor. When the
output driver temperature reaches 150°C the
respective output channel is automatically
turned off to avoid material damage to the IC.
Five types of diagnostics are available on the
IC level.
Vbb monitoring [UV, MV, W4P]: Of all of the
IC-level diagnostics, Vbb-monitoring is prob-
ably the most important one. Vbb-monitoring
checks the voltage level on the driver output
side. The possible reasons for this voltage
failing and falling below the normal operation
level could be that the power supply is not ad-
equately designed for the loads, or the power
supply is simply beginning to fail. It is also
conceivable that the electrical connection be-
tween the power supply and the switching IC
is gradually increasing its ohmic resistance, i.e.
corrosion may be at work. In a large number
of applications the nominal supply voltage
(Vbb) on the factory side is 24V +/-20%. How-
ever, if that voltage drops to a level as low as 9V,
the outputs are turned off while it is still
possible to do so. This is not done without a
pre-warning. As a matter of fact, there are two
intermittent stages: if the supply voltage drops
below 16V then an under-voltage warning
[UV] is issued. At that voltage the performance
level of outputs of the IC is not yet compro-
mised. The UV feedback provides a pre-warning.
If the supply voltage drops further, i.e. to a
level of 13V and below, then a missing voltage
warning [MV] is sent. At this supply voltage
level, the IC outputs are still working. However
one may be well advised to perform a controlled
system shut-down while it is still possible. Only
if the supply voltage drops to 9V or less are all
outputs automatically turned off and a wait-
for-power [W4P] feedback triggered. In this
case the supply voltage has dropped to a level
too low for proper operation.
There are four additional IC-level feedbacks
available.
Overtemperature on IC-level [OTP]: In addition
to the temperature monitoring of each of the
eight output channels, the IC has a ninth tem-
perature sensor. This additional sensor provides
overtemperature protection on IC-level. The
threshold is set to 125°C in order to remain
below the glazing temperature of standard FR4
PCB materials.When this threshold is exceeded
all outputs are automatically shut off (OTP).
P
OWER
M
ANAGEMENT
Figure 2. Many integrated diagnostic capabilities are available in the single IC. This eliminates
the need to develop complex and space consuming circuit layouts based on multiple discrete
components
