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ADC12DJ5200RF: power supply

new2day
Expert 1950 points
Part Number: ADC12DJ5200RF
Other Parts Discussed in Thread: ADC12DJ3200, TPS74401, TPS7A7200, TIDA-01027

ADC12DJ5200 is pin compatible with ADC12DJ3200, which means it can be used as drop-in without any changes. 

I've looked at the documentations or application notes about power supply design (TIDA-01027). It suggests using TPS7A8400A  for both 1.1V and 1.9V to the ADC instead of TPS74401 (1.1V) and TPS7A7200 (1.9V). 

I like to check and or confirm a couple things:

1. would it be fine to use TPS74401 (1.1V) and TPS7A7200 (1.9V) without any performance degrading? 

How much would be degraded, such as SFDR etc. 

2. do you have test results by using either LDOs? two TPS7A8400A  vs. TPS74401 (1.1V) and TPS7A7200 (1.9V). 

Thank you.

  • 0
    TI__Mastermind 39340 points

    Hi,

    Unfortunately, we don't have results comparing the 5200RF ADC with various LDO/power supply designs.

    Even though the output noise of the TPS7A8400A LDO, which is on the current EVM, is lower than the TPS74401 and TPS7A7200 LDO's. it should be fine.

    This there was an issue, it would affect SNR not SFDR so much....unless you use a typical switcher design.

    If you assume the ADC's PSRR to be 40dB (which it is, we have measured it), then you can start to address this by a simple calculation to understand the tradeoffs.

    Take the TPS74401 LDO, it has roughly 17.6uVrms output noise. You can assume this noise is white.and the PSRR of the ADC will suppress this by -40dB. This means the noise is actually....176nVrms. 

    Now, lets look at the 5200RF ADC's noise...For JMODE1, the FS=0.8Vpp, and has an SNR of 55dB, Fs = 10.4GSPS. Back-calculate and the ADCs' noise is 503uVrms. which is much higher than 176nVrms. So, you should be fine if you plan to go this route.ADC12DJ5200RF_EVM_SCH_RevA.PDF

    Lastly, we have a switcher design for the 5200RF that was also evaluated. I attached the schematics if interested. This design was proven out and yields the same ADC performance specifications. Plus you will get the added efficiency and smaller size. 

    Regards,

    Rob