Datasheet

Data Sheet 31 Rev. 2.1, 2011-09-01
PROFET™+ 12V
BTS5045-2EKA
Diagnostic Functions
7.3.3 SENSE Signal in Open Load
7.3.3.1 Open Load in ON Diagnostic
If the channel is ON, a leakage current can still flow through an open load, for example due to humidity. The
parameter
I
L(OL)
gives the threshold of recognition for this leakage current. If the current I
L
flowing out the power
DMOS is below this value, the device recognizes a failure, if the DEN (and DSEL) is selected. In that case, the
SENSE current is below
I
IS(OL)
. Otherwise, the minimum SENSE current is given above parameter I
IS(OL)
.
Figure 24 shows the SENSE current behavior in this area. The red curve shows a typical product curve. The blue
curve shows the ideal
k
ILIS
ratio.
Figure 24 Current Sense Ratio for Low Currents
7.3.3.2 Open Load in OFF Diagnostic
For open load diagnosis in OFF-state, an external output pull-up resistor (R
OL
) is recommended. For the
calculation of pull-up resistor value, the leakage currents and the open load threshold voltage
V
OL(OFF)
have to be
taken into account. Figure 25 gives a sketch of the situation.
I
leakage
defines the leakage current in the complete
system, including
I
L(OFF)
(see Chapter 5.5) and external leakages, e.g, due to humidity, corrosion, etc.... in the
application.
To reduce the stand-by current of the system, an open load resistor switch S
OL
is recommended. If the channel x
is OFF, the output is no longer pulled down by the load and
V
OUT
voltage rises to nearly V
S
. This is recognized by
the device as an open load. The voltage threshold is given by
V
OL(OFF)
. In that case, the SENSE signal is switched
to the
I
IS(FAULT)
.
An additional
R
PD
resistor can be used to pull V
OUT
to 0V. Otherwise, the OUT pin is floating. This resistor can be
used as well for short circuit to battery detection, see Chapter 7.3.4.
I
IS
I
L
Sense for OL .vsd
I
L(OL)
I
IS(OL)