LMD18400 Datasheet, PDF (14/26 Pages) National Semiconductor (TI) – Quad High Side Driver

LMD18400
SNVS094C – JUNE 1996 – REVISED APRIL 2013
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The diagnostic data can be read periodically by a controller or only in the event of a general system error
indication to determine the cause of any system problem. This general indication of a fault is provided by an
Error Flag output (pin 13). This pin goes low whenever any type of error is detected. There is a built-in delay of
approximately 75 µs from the time an error is detected until pin 13 is taken low. This is to help mask short
duration error conditions such as may be caused by driving highly capacitive loads (>2 µF). A lamp load may
generate a shorted load error for several hundred milliseconds as it turns on which should be ignored.
Figure 25. Serial Diagnostic Data Assignments
The Error Flag output pin is an open drain transistor which requires a pull-up resistor to a positive voltage of up
to 16V. Typically this pull-up is to the same 5V supply which is biasing the Enable input and any other external
logic circuitry. The Error Flag pins of several LMD18400 packages can be connected together with just one pull-
up resistor to provide an all-encompassing general system error indication. Upon detection of an error, each
device could then be polled for diagnostic information to determine the source of the fault condition.
A second direct output error flag is for an indication of Thermal Shutdown (pin 17). This active low flag provides
an immediate indication that the die temperature has reached +170°C and that the drive to all four switches has
been removed. This output is pulled up to the internal 5.1V logic regulator through a small (5 µA) current source
so use of a buffer on this pin is recommended.
Figure 26. Thermal Shutdown Flag and Shutdown Input
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