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LM25037: Comp pin

Simon Reuning
Prodigy 20 points
Part Number: LM25037


Hello, 

My question is related to the comp pin.

I have the internal Op Amp disabled by tying the FB pin to ground per datasheet. 

I want to drive the Comp Pin directly with an external Op-Amp. 

Now looking at the Absolute Maximum table the datasheet states that the 'Comp pin is an output and TI does not recommend connecting external power sources'.

A little bit further up in the pin description the datasheet states that the 'Comp pin is an I/O and described as input to the pulse with modulator.'

In Figure 12 it is also described as Input for a voltage feedback.

I went ahead and tested it out and was able to drive that pin directly and got the results i was hoping for.

I need to know what my absolute maximums are on that pin and if i have to use an open-collector op amp. 

 

  • 0
    TI__Mastermind 34465 points
    Hello Simon,
    Sorry about the confusion in the data sheet. Sometimes the wording used is not clear and may appear contradictory.
    So the first thing you did is to disable the internal OPAMP by tying FB to GND.
    This OPAMP has an open drain output so tying FB to GND allows COMP to reach 5V through a 5k internal resistor.
    So if you want to externally control COMP your circuit needs to pull down on COMP either with an open drain or open collector.
    You cannot apply a voltage directly into COMP.
    If you are using an external OPAMP you need to connect its output to a transistor drive and connect the collector of the transistor to COMP.

    The Absolute Maximum Ratings table does not list a value for COMP or RES because even though they can be configured as inputs you should never apply an external voltage to these pins. You can control these pins voltages by pulling down on the pins.

    Regards

    John