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UCC14241-Q1: Can be used to power Operational Amplifiers?

Pier Mauro Margotti
Prodigy 10 points
Part Number: UCC14241-Q1

Tool/software:

Hello,

Would it be possible to power a circuit that uses two Operational Amplifiers with the UCC14241? I kind of got to the conclusion that the presence of operational amplifiers makes the  UCC14241-Q1 enter a protection mode just few ms after starting up, and provides no power. Without the operational amplifiers or sometimes with just one operational amplifier, it seems to work correctly.

By the way, the Operational Amplifiers are believed not to source or sink any current, at least during the power-up sequence.

Many thanks and kind regards.

  • 0
    TI__Mastermind 31595 points

    Is this for a bipolar opamp where you need +VCC/-VCC or single output bias where you only need +VCC/GND? If bipolar, you need to make sure the UCC14241-Q1 can handle any load imbalance that might occur between +VCC/-VCC. The dual output of UCC14241-Q1 operates using a split capacitor output (two caps in series) and needs to maintain charge balance for the outputs to remain in regulation. The ratio of voltage is proportional to the ratio of the capacitors and is the loading become too asymmetrical such that the voltage on VEE-COM begins to decrease, the output may get into UVLO and shut down.

    Please use the UCC14241-Q1 Excel Design Tool to optimize the capacitor ratio and RLIM for dual output or just setting up the UCC14241-Q1 in single output.

    Regards,

    Steve

  • +1 in reply to Steven Mappus1
    Prodigy 10 points

    It is for bipolar indeed. The Excel Design Tool did not show any issue but the VDD-to-VEE or (VDD-COM) output of the UCC14241-Q1 stops rising as it reaches less than 1 V (I guess VVDD_UVLOS), then, I guess once elapsed the tSOFT_START_TIME_OUT, the outputs fall back to zero. If I cycle VIN or the ENA, the above repeats, with very slight variations from instance to instance.

    I can measure several tens of kOhms between VDD-COM-VEE, sign that there's not some short (i.e. without power). After trying several combinations of capacitors and RLIM (trying to increase the charge output of the UCC14241-Q1), I started removing components that I thought might perhaps be drawing current during the start-up, till I decided to remove also the OpAmps, then the UCC14241-Q1 worked as expected. So I concluded they were the culprits and I came to you asking whether you could confirm or reject my guess, i.e. that OpAmps may not be necessarily suitable to be powered by the UCC14241-Q1 without any precaution. By the way, I tried "traditional" OpAmps so far, i.e. which do not incorporate any advance feature such as Power-On checks before starting operation.

    Kind Regards,

    Pier Mauro

  • 0 in reply to Pier Mauro Margotti
    TI__Mastermind 31595 points

    Sounds like the bipolar op amp is presenting an asymmetrical load to the UCC14241-Q1? One option is to try and skew the capacitor divider to compensate for the asymmetrical load from the op amp? You would need to account for the additional load on VDD and VEE separately as you see in the Excel tool. Also, set up the RILM as RDR as described in the Excel tool.

    Regards,

    Steve

  • 0 in reply to Steven Mappus1
    Prodigy 10 points

    Many thanks for the support.

    In facts I have eventually found an issue with the implementation of the schematics, which concerned the Op-Amps. Once corrected the card and resolved the issue, I can confirm that the UCC14241-Q1 powers correctly the Op-Amps and that the values of the capacitors as well as RLIM originally chosen through the Excel tool do provide the expected result.