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AFE7920: Abnormal output at the moment of power failure

Zach Zhu
Prodigy 260 points
Part Number: AFE7920

Tool/software:

Hi,

My customer has a problem using AFE7920. 

Ch1 is the output of AFE Tx Balun, Ch2 is the PAU enable given by the system for triggering, and Ch3 is the power supply of TXAP/TXAM 1V8 in front of AFE Tx balun.

Under what circumstances will the chip show an abnormal output at the moment of power failure?

BR,

Zach Zhu

  • 0
    TI__Expert 4330 points

    Hi Zach,

    As per the datasheet, TI cannot guarantee functional operation of the device beyond what is listed in the Recommended Operating Conditions (section 8.3). The 1.8V rail supplies the TX, the TX DAC, and the PLL, so a power failure on the 1.8V rail may lead to an abnormal TX output.

    We have two options to catch this - one would be the PAP (power amplifier protection), which can be configured to trigger on PLL loss of lock and then disable the TX output. However, since the PAP also runs off the TX clock, and there is some clock disturbance, we may not be able to turn off the TX immediately upon seeing this error. Please refer the customer to section 7 of the Configuration Guide for more information on PAP. The other option would be to configure the ALARM pins to go high on PLL unlock errors. This way, when the customer sees the ALARM pin go high, they can turn off all the TX output using either GPIO or C API override functions. Please refer the customer to section 8.4 of the configuration guide for more information on the ALARM pins.

    Thanks,

    Aman