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OPA547: - clarification about the appropriate R value for ILIM pin / Why is VOUT limited to 1.4V?

AnBer
Mastermind 28890 points
Part Number: OPA547

Team,

This is a follow up of the below E2E post where Raymond Z. helped with:
https://e2e.ti.com/support/amplifiers/f/14/p/899491/3325820#3325820

It seems that in some of the boards the VOUT gets limited to 1.4V when the resistor on VLIM is equal to 750k.
What could be the reason?
I can share the schematics off-line if needed.

Thanks in advance.

A.

  • 0
    TI__Guru* 93105 points

    Hello AnBer,

    If RLIM is set to 750 k, the OPA547 maximum output current (Imax) is programmed to approximately 33 mA. If the output voltage tries to swing beyond what 33 mA limiting permits, the output will clip at the voltage level equal to RL x Imax. If you remove the output load or increase its resistance you will likely see the output swings to a much higher voltage when the input voltage is increased accordingly.

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • 0
    TI__Mastermind 47966 points

    Hi AnBer,

    Can you send me the schematic?

    Rcl = 750kohm will limit the OPA547's current to approx.30.4mA. The constant output current is approx. 12.2mA. If the output load is not changed at 150 ohm, the output voltage should be 150Om*12.2mA = 1.83V. 

    Speculation: If the output Rload = 1.4V, the Rload = 1.4V/12.2mA = 114.8 ohm. What is the tolerance of the load resistor?

    The current limit tolerance per the datasheet is specified at +/-30mA. I was wondering if the value of Rcl resistor needs to be lowered slightly. 

    Best,

    Raymond

  • 0
    TI__Genius 10850 points

    Hi AnBer,

    We haven't heard from you in a while. We hope the issue was resolved. Closing this thread now. Reply to re-open if you have any additional questions.