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LP38798: PSRR -- Vout 16V, Iout 3.5mA

steve wenner
Expert 2355 points
Part Number: LP38798
Other Parts Discussed in Thread: TLV61046, TPS7A47,

Good evening....

I have an application that deals with 16.5V, extremely low level signals and large gains.  The datasheet for the above subject shows much PSRR data for Vout = 5V and some data to support Vout =1.2V but nothing to support higher voltages.  Can you please share with me some internal data for PSRR and noise with respect to voltages up at Vout = 16V with light load 3.5mA?  Also the EVM doesn't seem to support the high voltages, is there a reason that the EVM doesn't have provisions to set the output voltage to say 15V for testing purposes?

Thank you

Steve 

  • 0
    Expert 2355 points

    Quick follow up to that...

    I have been also looking at the TPS7A4701...  Trying to decide on the better solution? (any comments would be appreciated) I like the LP because piece price is cheaper.

    The end application is using a boost converter (TLV61046) that drives the LDO.  The light current causes the boost to go into burst mode with a pronounced spectral energy around 38kHz (ie 3.5mA load draw).  The input voltage to the LDO is 16.695V with the output of the LDO 15.6V.

    thanks

    Steve 

  • 0 in reply to steve wenner
    TI__Mastermind 43630 points

    Hi Steve,

    Both are great parts. PSRR performance is more affected by the delta between VIN and VOUT than the actual voltages. The LP38798 was designed with the goal of having the highest possible PSRR with excellent noise performance. The TPS7A47 was designed with the goal of having the best noise performance with excellent PSRR.

    For both, noise does gain as a function of VOUT. the TPS7A47 has a plot showing this:

    Given your load is so light (i.e. the PSRR should be great for both at this load), I would think that the TPS7A47 might be the better option.

    I do not have data on the LP38798 at 15V at VOUT.

    I hope this helps.

  • 0 in reply to JCHK
    Expert 2355 points

    John...

    Thank you so much for the response!  I was inclined to lean in that direction.  Can you tell me for what you know about my given application (HIGH PSRR, low noise) is it better to use resistors to get Vout or use the ANY OUT Programmable pins ? (I could use Vref + 6P4V1 + 6P4V2 + 1P6V)

    Thanks

    Steve

  • 0 in reply to steve wenner
    TI__Mastermind 43630 points

    Hi Steve,

    You're welcome. Any-Out has advantages with respect to solution size, accuracy, and a very minor benefit in no additional noise added from the feedback resistors. If you can get the voltage you want with Any-Out, this is a good option.

    Regards,