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TLV1702: Window Comparator: Outputs are shorted.

shiwei luan
Intellectual 750 points
Part Number: TLV1702
Other Parts Discussed in Thread: TLV1701

In the datasheet, the TLV1702 has a window comparator example. The outputs of two TLV1702 are shorted. If one output is High, the other is Low, will this cause any problem?

Thank you.

  • 0
    TI__Guru 53826 points

    Hello Shiwei,

    This is an "OR'ed" output. Either comparator can pull the output low.

    The TLV1701 outputs are "Open Collector", and can only pull low. Think of them like a relay switch to ground. Look at the Block Diagram on page 11 of the datasheet. Notice that the output pin only has one transistor to ground (V-).

    The outputs cannot pull high on their own and require the pull-up resistor (Rpullup) to go "high".

    Since each output can only connect to ground, there is no current flow between the outputs, so they will not damage each other.

    Comparators come in two main output types, "Open Collector" (or "Open Drain" for CMOS), that only pulls low .The other type is "Totem Pole" or "Rail-to-Rail" output, which can sink and source current (this is the type of output you were thinking of).

    *IF* these were "Totem Pole" outputs, then NO, you cannot connect those types of outputs together as one output would short the other if the output states are different.

    So the circuit is ok, and actually quite common. But you need to use the correct output type (Open Collector).