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OPA454: OPA454 start up current

Kailyn Chen
Genius 9560 points

Part Number: OPA454
Other Parts Discussed in Thread: OPA445,

Hello,

What is the power up current of OPA454 and OPA445? Because our customer find that if the supply current is lower 2A of OPA454, the power would be damaged, while the OPA445 could worked normally, so what  are the differences between  OPA445 and OPA554 during power up?

  • 0
    Guru 140200 points

    Hi Kailyn,

    what do you mean by "...if the supply current is lower 2A of OPA454, the power would be damaged..."?

    Hhm, I don't think that the OPA454 and OPA445 have "power up currents" themselves. If there is a considerable power up current then this might be caused by the load. But the short circuit current is limited to about 170mA for the OPA454 which is far away from 2A. On the other hand, the short circuit current of the OPA445 is much lower, only 26mA. This could explain why the OPA445 is working in your circuit and the OPA454 not. Or is the power up current coming from the rest circuitry?

    Kai

  • 0
    TI__Guru* 93105 points

    Hi Kailyn,

    The OPA445 and OPA454 are high-voltage Op amps, but their nominal operating currents are low on the order of a few milliamperes. I would not expect for either Op amp to draw significantly higher current, more than a few milliamperes, during normal V+/V- power up. Sometimes with Op amps there can be power up conditions that result in higher than expected supply current being drawn. An example of this is unequal start-up times for dual (+/-) supplies i.e. the positive supply comes up much sooner, or later, than the negative supply. In such cases an internal latch condition may be encountered and the current drawn by the Op amp can be much higher than normal. We haven't had any reports of the OPA454 having this behavior, but we can't possibly know all the different ways customers might apply supply voltages.

    If the OPA454 is exhibiting this behavior adding transient voltage suppressor diodes from V+ and V- to ground nearly always remedies the problem. We can discuss that option more if it turns out there is a latch condition. 

    If you can provide the OPA445/OPA454 circuit schematic with detailed supply, input voltage and load information, we can review the circuit. Additionally, DSO images of the supply V+ and V- voltage and current during power up to the two devices could prove be very helpful.

    Does the customer have the OPA454 underside PowerPAD connected to V- on the PC board? See 12.1.2 PowerPAD Layout Guidelines #1. The PowerPAD must be connected to the most negative supply voltage on the device, V–.

    Regards, Thomas

    Precision Amplifiers Applications Engineering