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OPA2170: Can OPA2170 short-circuit output current limits be adjusted to custom levels during test process at TI?

Part Number: OPA2170

Can OPA2170 short-circuit output current limits be adjusted to custom levels during test process at TI?

  • Hi Dave,

    Could you elaborate on your need a little bit? Do you have concern about the distribution of short-circuit output currents? I'm wondering if we'd be able to find you an alternate part which exhibits the specification you're looking for.

    That said, generally we don't provide this type of adjustment/customization and the parts are tested to meet the datasheet specs.

    If you'd like to take this conversation offline, please send me a friend request and we can discuss further.

    Thank you,
    Paul
  • In reply to Paul Goedeke:

    HI Paul. This is for analog output on precision scientific instrumentation. The opamp is driven by DAC60004 to generate 0-5V or 0-10V signal.

    I need a single supply(4-35V) opamp with low input offset(on the order of 1-2mV for worse case, but lower is better), whose input includes GND, and whose output can swing within a few millivolts of ground.

    I'm interested in short-circuit limits because the output of this opamp circuit is customer facing and be connected to GND or 32V. If the short-circuit current limit is low enough and the thermal resistance of the package is low enough, then the op-amp won't overheat. From my testing it seems that short-circuit current limit on sinking current is especially important.

    OPA2170 short-circuit sinking current is 20mA or less.

    If output is connected to 32V, and sinking 20mA, then 150 ohms used for RISO compensation dissipates 60mW and has 3V drop across it.

    OPA2170 dissipates(32V-3V)*20mA =  580mW. In a WSON package 580mW*71.5C/W = 41.47C temperature rise, which is respectable. 

    If the circuit-circuit sinking current limit were lower, it'd be better because the OPA2170 would dissipate less heat.

  • In reply to Dave Knight:

    The OPA2170 tested well on the bench. The only thing that'd make it better would be if its output sank less current when short circuited to 32V.
    The OPA2237 looks like it might be promising. I haven't tested it. It has lower short-circuit sinking limit, but it's thermal characteristics aren't as good as the OPA2170 WSON.
  • In reply to Dave Knight:

    Thanks for the additional info Dave. I'll share this with the team and get back to you with some thoughts. With the upcoming holidays, please allow for some delay in the reply.

    Thanks,
    Paul
  • In reply to Dave Knight:

    Dave,

    R31 resistance value is the only way to limit current for 32V. The reason is the internal diode from U15A output to U15A pin8. This diode is just a diode and won't actively limit current.

    Try measuring pins 1 and 8 when 32V is applied to see that PIN1 > PIN 8

    Regards,
    Ronald Michallick
    Linear Applications

    TI assumes no liability for applications assistance or customer product design. Customer is fully responsible for all design decisions and engineering with regard to its products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning Customer's design. If Customer desires engineering services, the Customer should rely on its retained employees and consultants and/or procure engineering services from a licensed professional engineer (LPE).

     

  • In reply to Ron Michallick:

    Ronald,
    D1 in the schematic limits the current through the internal diode from D15A output to U15A pin 8. When 32V is applied to pin 1, pin 8 tracks pin 1, but it's not destructive because of the low current and does not exceed the opamps voltage rating.

    I'm more specifically interested in limiting the current sinking ability of the op-amp, or finding a part similar to the OPA2170 with a lower short-circuit sinking limit.
    Regards,
    Dave
  • In reply to Dave Knight:

    Dave,

    Oh yes, the D1 diode. I didn't scroll up high enough the see that diode this morning.
    VCC and VOUT will increase in current limit as you have seen. Power dissipated is IOUT * VOUT so lowering VOUT and IOUT will be helpful.
    One other plan is to make output try to go high if output is greater than VCC. That would greatly reduce current.
    Do you have your circuit in Ti-Tina that you can upload?

    Regards,
    Ronald Michallick
    Linear Applications

    TI assumes no liability for applications assistance or customer product design. Customer is fully responsible for all design decisions and engineering with regard to its products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning Customer's design. If Customer desires engineering services, the Customer should rely on its retained employees and consultants and/or procure engineering services from a licensed professional engineer (LPE).

     

  • In reply to Ron Michallick:

    Ron,
    How do you recommend making the output go high if the output is greater than VCC?
  • In reply to Dave Knight:

    Dave,

    This modified circuit should provide full sink current until op amp V+ pin starts to rise,  at that point the output is suppose to go high so the output will not fight the external voltage anymore and op amps' V+ will rise with just a little current to run the PNP transistor.

    However, that doesn't model well. It won't solve if voltage starts at 32V but will solve for voltage ramping to 32V (DC transfer function). Also current doesn't drop and op amp's ground current flows in the wrong direction most of the time.  

    I will need to build this to prove it out.

    8688.opa2170 analog output(with high voltage input reversal).TSC

    So the worst case should be external voltage close to 12V and low current above that.

    Regards,
    Ronald Michallick
    Linear Applications

    TI assumes no liability for applications assistance or customer product design. Customer is fully responsible for all design decisions and engineering with regard to its products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning Customer's design. If Customer desires engineering services, the Customer should rely on its retained employees and consultants and/or procure engineering services from a licensed professional engineer (LPE).