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Original question:

TPS793475-EP: TPS793475 LDO - PSRR

TPS7A47: Vdo vs PSRR

Yusuke Mukuno
Expert 7395 points
Part Number: TPS7A47

Hi expert,

My customer have a request.

Could you please give me the Vdo vs PSRR data like figure16 at Vout=15V? (TPS7A47)

Also, in case of TPS7A3301, please give me same data at Vout=-15V?

I had understood that the PSRR is not depend on the Vdo.

However, if the input voltage is near to Vout+Vdo, I seem, it is affect to PSRR. (from the following E2E session)

Could you please let me know the reason for it?

In case of TPS7A41 figure16,

Datasheet spec is Vdo=450mV(max) at 1A load.  However, The PSRR at Vdo=500mV is lower around 10dB than PSRR at Vdo=1000mV.

 Vdo at both conditions meet the datasheet spec, I cannot understand the reason about this difference...

Thanks

Muk

  • 0
    TI__Mastermind 23361 points

    Hi Muk,

    Please see my comments below your questions.

    My customer have a request.

    Could you please give me the Vdo vs PSRR data like figure16 at Vout=15V? (TPS7A47)

    --The LDO's output can be set to anywhere between 1.5V to 34V, and it's impossible to include every combination when we validated the IC. Instead, we normally pick the common voltage rails for the majority of our test. As for your question, I understand the VDO vs PSRR plot in Figure 16 was taken with the 3.3V output, but the difference between different output voltages of the LDO is only the gain on top of the FB voltage. At similar VDO, the PSRR performance across different voltage is comparable. You may also show Figure 18 to your customer, and based on Figure 18, the 15V output could have 15dB lower PSRR comparing to the 3.3V output with a frequency less than 100Hz, the rest of the PSRR performance should be similar to the one with 3.3V output.

    Also, in case of TPS7A3301, please give me same data at Vout=-15V?

    --Similar to what I have explained for the previous question, please use Figure 19 to help the customer pick the VDO based on their PSRR needs.

    I had understood that the PSRR is not depend on the Vdo.

    --PSRR is highly dependent on the VDO to a certain point. In general, high VDO will imporve PSRR.

    However, if the input voltage is near to Vout+Vdo, I seem, it is affect to PSRR. (from the following E2E session)

    --Yes, if the headroom is just output + the minimum Vdo, the PSRR performance will be less than optimal.

    Could you please let me know the reason for it?

    --You may find more details in the last paragraph on Page 2 of this app note:

    www.ti.com/.../slyt202.pdf

    In case of TPS7A41 figure16,

    Datasheet spec is Vdo=450mV(max) at 1A load. However, The PSRR at Vdo=500mV is lower around 10dB than PSRR at Vdo=1000mV.

    Vdo at both conditions meet the datasheet spec, I cannot understand the reason about this difference...

    --This is another example that VDO is determining the PSRR performance, you may find more details in the app note I posted in your last question.

    Regards,
    Jason Song