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ISOM8110: How could I use the ISOM8110 to control an LM25037?

Istvan Adam
Prodigy 90 points
Part Number: ISOM8110
Other Parts Discussed in Thread: LM25037,

Tool/software:

Hi,

I’m designing a push-pull converter using the LM25037, and I would like to implement the isolation with an opto-emulator.

I read in the ISOM8110 datasheet that the minimum forward current is 0.5 mA.
The COMP pin of the LM25037 has an internal 5 kΩ pull-up resistor.
In steady-state, the voltage at the COMP pin is around 1.2 V, which means that approximately 760 µA flows through the ISOM8110’s output transistor.
Assuming a current transfer ratio (CTR) of 180%, the LED current would be around 422 µA — which is below the minimum 0.5 mA specified.

Is it possible to use the ISOM8110 with the LM25037?

Could I perhaps add a pull-up resistor to the COMP pin to increase the current through the transistor?

  • +1
    TI__Mastermind 28515 points

    Hello Istvan, 

    Thank you for your interest in our part.

    "Could I perhaps add a pull-up resistor to the COMP pin to increase the current through the transistor?"

    • Yes, a pull-up resistor is needed to increase the current through the transistor and diode-emulator input for controllers where the forward current is below the minimum IF of 0.5mA.

    Best,
    Andrew 

  • 0 in reply to Andrew J
    Prodigy 90 points

    Thank you for your help! I’m going to use a 3.3 kΩ resistor, so the resulting pull-up resistance will be 2 kΩ. You are the best! :)