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Original question:

TPS7A84A: how to measure the LDO noise density spectrum

TPS7A84A: TPS7A84A PSRR test

user4073964
Prodigy 20 points
Part Number: TPS7A84A

there is an interesting issue when I was test the PSRR. As we know, it is better for us to remove the input cap, the input caps of TPS7A8400 are removed. If connect the board directly to the power supply, there is about 26kHz reponse on Vin which cause large votlage spike on input, when the load is higher than 0.6A, output voltage drops. could  anyone tell me how to remove this spile without adding any cap or filter that affects the injuected signal.

the PSRR test needs injected input signal.

  • 0
    TI__Mastermind 23361 points

    Hi, 

    I am not sure what is causing the spikes on your input supply. But those voltage spikes can normally be improved by reducing the inductance from your supply to the board, and also by reducing the input supply's impedance. I would recommend making the cable from your supply as short as possible to reduce the inductance. 

    Here is an app note discussing how to measure PSRR in the lab, please see this link. In our lab, we have a custom-built board that allows us to inject AC test signal on top of the DC operating point. We then use the signal analyzer to collect the response at different frequencies. 

    http://www.ti.com/lit/an/slaa414a/slaa414a.pdf

    It's hard for us to remotely helping you with measurements on your own setup, but if there is some pieces of information you are trying to get from PSRR, please let me know, and we may be able to help. 

    Regards, 
    Jason Song