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TPS7A4501-SP: Quiescent current vs ground current for light current loads

Aieie
Prodigy 50 points
Part Number: TPS7A4501-SP

Tool/software:

Hi there, 

in the TPS7A4501-SP datasheet (SLVSC31D revised Aug 15), for Vin=18V the typical ON quiescent is <0.8mA, with an output load of 4.3k (with a typical 0.2mA variation over temperature, for Vin=6V and no load).
So in this value there is already a light output load.
This quiescent current figure is in line with the headline value of <1mA quiescent current for the part.

Where I am not super clear is with 'ground current' plots: Figure 7,8 in particular seems to suggest there an additional 1mA ish for light loads (i.e. <25mA). Is that correct? 
So am I right in saying that if we have an output current of 25mA,  then we have to add quiescent current+ground current is about 2mA (typical at ambient)?
Or if Figure 7 already taking into account the 1mA quiescent current and so the total (non-load current) is 1mA?

Thanks

Regards

  • +1
    TI__Genius 12010 points

    Hello,

    Your last statement is correct.

    Ground current is the difference between the input and output currents, while quiescent current is more specifically the current used by the internal circuitry of the device itself. This means ground current includes quiescent current. Quiescent current is measured while the device is as near to no-load operation as possible. The feedback resistors themselves do create a very small load, so this is noted in the test conditions (4.3kOhm equivalent that you highlighted, for example).

    Let me know if there's any further clarification I can add.

    All the best,

    Sarah

  • 0 in reply to Sarah Koch
    Prodigy 50 points

    Hi Sarah,

    thanks so much for your quick reply!

    OK, so moving forward I will just refer to Figure7 and 8, as that is the total non-load wasted current.

    In hindsight, perhaps they could have measured the quiescent current with Vo=1.21V and no load, so not to measure any load current at all (no divider at the output) and without any waste current proportional to the load (as in Figure8).


    To be honest, by looking at Figure 8 the non-load current increases exponentially with higher loads, so the claim that the quiescent current is 1mA is really only true for loads around 10mA or so.. no? 

    Thanks for your help

    Regards

  • +1 in reply to Aieie
    TI__Genius 12010 points

    No problem!

    To your point, it looks like Figure 3 does show a quiescent current test performed with true no load. It's not clear whether the same units were used but ultimately it does appear to produce roughly the same result as the test in Figure 5 that had FB resistors, so the extremely small load the FB resistors create can be considered nearly negligible. The graphs are gathered from one unit while the Electrical Characteristics table values are based on a larger sample of units, so there can be some small differences due to part-to-part variation but they do agree with each other.

    The measured unit in the graphs shows roughly Iq=~0.7mA @25C and the table suggests an average of 1mA. 

    Thanks,

    Sarah