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TPS7A4501-SP: ADJ bias current

Joseph Samrani
Prodigy 20 points
Part Number: TPS7A4501-SP

Tool/software:

Hello,

The data sheets list the ADJ Bias current range between typical = 3uA to max = 7uA at 25 degC. However, figure 13 graphs the temperature vs ADJ current to be be close to ~1.5uA at 25 degC and at 125 degC is less than 3uA.  I know still very small current, but it does make slight difference when performing WCA.  For analysis purposes which is the better representation of the ADJ bias current, figure 13 or the values in the table?  Thank you.

Regards,

Joseph. 

  • +1
    TI__Genius 12090 points

    Hi Joseph,

    The graph represents a single unit, while the electrical characteristics table encompasses part-to-part differences and other sources of variation across a sample of units. The electrical characteristics min/max limits also have some statistical guard-banding applied, so they would be the more conservative of the 2 sources. 

    Thanks,

    Sarah

  • +1 in reply to Sarah Koch
    Prodigy 20 points

    Hello Sarah,

    I have another question about this LDO. I am using two LDOs to generate 3.3V and 1.5V rails for uC, where both LDOs are powered from the same 5V supply. The 1.5V has to come up prior the 3.3V rail based on the uC power up requirements, I am thinking of couple of options:

    1- Use the1.5V rail and connect it to the 3.3V LDO shutdown pin, then the 1.5V is on prior 3.3V. However, the shutdown pin input range is 0.9V to 2V, will this cause the 3.3V not come on fully or be in some undetermined state?

    2- Instead of connecting the 1.5V to the 3.3V shutdown pin, I thought of connecting an RC circuit to the shutdown pin on 3.3V LDO. Therefore, when the 5V comes on, the 1.5V will be on prior the 3.3V based on the RC constant connected to 3.3V shutdown pin.  Does the shutdown pin expect transition from low to high over specific time or just looking for a thrush hold level?

    Thank you.

  • 0 in reply to Joseph Samrani
    TI__Genius 12090 points

    Hey Joseph,

    The SHDN pin operates based on whether the enable/disable threshold has been passed. It is not a gradual turn-on or turn-off. Since the max SHDN pin enable threshold could be as high as 2V, using the 1.5V output to enable the 3.3V device carries some risk that there could be cases where the 3.3V device is never enabled. The RC approach could be a feasible alternative since SHDN is looking at whether the threshold has been passed. 

    Depending your design goals and timeline, you might also consider the TPS7H1121-SP as an alternative LDO to help simplify your design. It comes with a power good pin, in addition to soft start and current limiting functionality.

    Thanks,

    Sarah