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Original question:

TPS783: measured Iq is 6x higher than specified in the datasheet

TPS783: TPS783 quiescent current in Dropout mode (Vin-Vout <= 0.5V)

Riccardo Dell'Oro
Prodigy 180 points
Part Number: TPS783
Other Parts Discussed in Thread: TPS7A03

Hello,

We are using a TPS78330DDC in a device where a backup battery is provided. During our tests we found that the quiescent current remain inline with the datasheet data for the given conditions (Vin >= Vout+0.5V) but rise in a consistent way when this condition is not met.

We choose the TPS783 for its characteristic "Dropout mode" that allows it to be operated (without regulation, of course) even with Vin equal or below Vout.

Now my question is: how can we predict the quiescent current for this device when it is working in the provided "Dropout" mode?

Thank you.

  • 0
    TI__Mastermind 23361 points

    Hi Riccardo, 

    When in dropout, the positive rail of the error amp inside the LDO is not high enough to push the output to the set voltage. When this is happening, the error amplifier drives the gate voltage of the pass FET to the rail, and the FET is fully on. This process could consume a lot of power, this is why during dropout, some of the LDO may see higher quiescent current when it's approaching the regulation zone from the dropout and the quiescent current will then drop significantly once in regulation. 

    For most of the LDO datasheets including this device, unfortunately, the quiescent current in dropout is not provided. If your application requires the device to stay in dropout for an extended amount of time, I would advise you to run your validation as this is not the LDO is intended to operate. 

    Regards, 
    Jason Song

  • 0 in reply to Jason Song
    Prodigy 180 points

    Hi Jason, thank you for your reply.

    In our application a 3V supplied microprocessor keeps control of the core system when external supply is not present. This goal is obtained using a power switch that rely on a 3.6V Lithium primary battery as backup element. When the battery voltage drop to the element end of life value, all active tasks are suspended BUT data retention and a powerless maintenance alert indication need to remain active. In this last state the whole system current consumption attest around 3-4uA, but unfortunately is exactly at that stage that the TPS783 quiescent current rise at a level even higher than that of the system itself. Lowering system supply to 2.5V could be an option, but this imply revising all the interfacing of the system to the external world, which appear prohibitive. Can you suggest another linear regulator with similar characteristics to the TPS783, but without this limitation when operating in Dropout mode?

    Thank you and Best Regards.

  • 0 in reply to Riccardo Dell'Oro
    Prodigy 180 points

    For the benefit of the readers, I found that the newly manufactured TPS7A03 device share the same basic characteristics of the TPS783 (with other several improvements) while keeping a nanopower behavior also in dropout mode.