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LM3481: Dynamic input current limit

Ronald Jansen
Prodigy 10 points
Part Number: LM3481

Tool/software:

Hello,

We use LM3481 for charging a buffer in photoflash applications.

Different customers have different requirements. Some require fast buffer charging and other prefer a lower charging current.

Because of that we are looking for ways to make the input current software selectable.

What if we add a resistor to the current sense input and pull it up through a DAC? This would create a bias voltage at the sense input.

For example:

Slope compensation resistor: 1k

Resistor from Isen to DAC: 9.1k

If the DAC would be set to 1V, the Isen input at 0A would be 0.1V

Given that the maximum sense voltage is 160mv, would that effectively reduce the peak current with 60%?

And would there be any pitfalls/side effects to take into account?

Thanks in advance for your input!

Ronald

  • 0
    TI__Mastermind 26970 points

    Hi Roland,

    Thanks for using the e2e forum.

    I understand you idea setting a current limit for the device, but I have no reference for an implementation like this.
    A concern about this approach is, that the current limit is used as an active regulation feature. Originally, it is meant as a protection feature, so the regulation in overcurrent state may become irregular.
    To have a clean and stable duty cycle even during current limit state, I would recommend the approach of using a shunt resistor at the output, and feed this signal through an amplifier into the FB or COMP pin. Basically adding a second regulation loop. This way you achieve a constant output current regulation.

    Please let me know if you have additional questions on this.

    Best regards,
    Niklas