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Ripple rejection of TPS79147 and TPS79101

Martin Turon
Prodigy 225 points
Other Parts Discussed in Thread: TPS791, TPS7A8101, TPS799

Hi,

I'm trying to find a chart describing ripple rejection PSRR vs. frequency of the TPS79147 (fixed 4.7V ouput) and TPS79101 (adjustable output).  Unfortunately, the datasheet only specifies these figures for the 1.8V and 3.3V output versions.  There is mention of 70dB PSRR at 10khz, which is helpful, but the plots for the TPS79118 and TPS79133 seem to contradict this number.  Does TI have such plots ripple rejection plots available for the two parts in question?

Thanks,

Martin

  • 0
    TI__Mastermind 41760 points

    Hi Martin,

    Unfortunately for this older device, we do not have data other than what's on the datasheet. The PSRR graphs in the datasheet show 70dB+ at 10kHz depending on the operating conditions. You may be able to get similar results with 4.7V and the adjustable as long as you keep the similar VIN - VOUT differential of 1V or higher. Since the TPS791 has a maximum recommended input voltage of 5.5V the 4.7V input/output differential will be 0.8V so the PSRR will be slightly lower. However, you can always improve PSRR performance by increasing the input/output cap.

    Regards,

    Darwin

  • 0 in reply to Darwin Fernandez
    Prodigy 225 points

    Hi Darwin,

    Thanks for the help.  What would your guess be on the PSRR at 15khz with 5.0V input?  Can the 4.7V fixed work well with such a low in/out diff?

    Also, do you think this family would have better PSRR at 15khz than TPS79901?

    Finally, would it be safe to output 4.833V with the TPS79101 given a 5.0V input?

    Regards,
    Martin

  • 0 in reply to Martin Turon
    TI__Mastermind 41760 points

    Hi Martin,

    It is very difficult to get high PSRR performance with 300mV and 167mV in/out differential. The TPS799 does not look like it will meet your requirements. You may need to increase your input voltage requirement and increase the output cap more to use the TPS791. The TPS7A8101 is a 1A device that is specifically made for PSRR, although, it may still be difficult to meet 70dB of PSRR with a 167mV in/out diff.

    Regards,

    Darwin