Datasheet

Data Sheet 18 Rev.1.0, 2008-04-29
BTS4175SGA
Diagnostic Mechanism
7 Diagnostic Mechanism
For diagnosis purpose, the BTS4175SGA provides a status pin.
7.1 ST Pin
BTS4175SGA status pin is an open drain, active low circuit. Figure 12 shows the equivalent circuitry. As long as
no “hard” failure mode occurs (Short circuit to GND / Over temperature or open load in OFF), the signal is
permanently high, and due to a required external pull-up to the logic voltage will exhibit a logic high in the
application. A suggested value for the
R
PU ST
is 15kΩ.
.
Figure 12 Status output circuitry
7.2 ST Signal in Case of Failures
Table 3 gives a quick reference for the logical state of the ST pin during device operation.
7.2.1 Diagnostic in Open Load, Channel OFF
For open load diagnosis in OFF-state, an external output pull-up resistor (R
OL
) is recommended. For calculation
of the pull-up resistor value, the leakage currents and the open load threshold voltage
V
OL(OFF)
has to be taken into
account. Figure 13 gives a sketch of the situation and Figure 14 shows the typical timing diagram.
I
leakage
defines the leakage current in the complete system, including I
L(OFF)
(see Chapter 5.4) 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.
Table 3 ST pin truth table
Device operation IN OUT ST
Normal operation L L H
HHH
Open Load channel L > V
(OL)
L
1)
1) L if potential at the output exceeds the Openload detection voltage
HHH
Over temp channel L L H
HLL
ST pin full diag.vsd
GND
ST
R
ST
ZD
ESD
R
PU ST
V
ccµC
Channel 0
Diagnostic
Logic