Vansco VMM3120, User Manual

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User Guide 37
Outputs
Note: How an output is de-rated is based on how all outputs are being used
collectively on the VMM3120.
There is one issue that must be addressed to determine the de-rating for low-side
outputs: Power dissipation.
Power dissipation
You must determine how much power is dissipated by each output. The total
allowable power dissipation inside the VMM3120 must be less than 7 W, which
will eliminate the need for additional heat sinking. Most of the power dissipation
comes from the output drivers.
The following calculation is used to determine how much power is dissipated by
the output drivers:

IoutN = output current for output N

RdsonN = 0.09Ω or 0.06Ω (resistance of the high-side or low-side output
FET, respectively) for output N
4.2.4. Low-Side Outputs with Current Sense Diagnostics
The VMM3120's low-side outputs have the ability to report many different fault
conditions, and are protected against short-circuit and over-current, open load,
and short-to-ground faults.
4.2.4.1. Short Circuit
Short-circuit faults occur when a low-side output pin is shorted to battery and
produces an output current above the specified over-current trip point, causing an
over-current on the circuit.
When a short circuit or over-current fault is detected, the software automatically
turns off the output.
The short circuit trip time for low-side outputs depends on how the outputs are
configured.
The application software can be used to reset an output from a short circuit or an
over-current fault by turning the output off and then on again.