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TPS7A83A: VBIAS PSRR vs Frequency

Tomasz Krupski
Prodigy 170 points
Part Number: TPS7A83A

Hi, is the "Figure 7-8 VBIAS PSRR vs Frequency" correct? When I compare it to "Figure 7-7 PSRR vs Frequency and COUT" the only difference is Cout (67uF vs. 22uF and 100uF). The frequency scale is the same. The PSRR on the Figure 7-8 is exceptionally high. Do Cout different values have such a high impact on PSRR ?

  • +1
    TI__Mastermind 47225 points

    Hi Tomasz,

    Figure 7-7 shows the PSRR vs. frequency from VIN to VOUT, and Figure 7-8 shows the PSRR vs. frequency from VBIAS to VOUT. This is to say that the VBIAS rail usually does not need much filtering because its PSRR is very high even up to 10MHz. To answer your question about different COUT values, PSRR is only affected by COUT at frequencies outside the bandwidth of the error amp (usually > 100kHz), as you can see in Figure 7-7, unless COUT is very large (some devices can support > 1mF). 

    Regards,

    Nick