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TPS7A8300: Issue

Part Number: TPS7A8300

We are using TPS7A8300RGWT in our design to generate 1V and 1.2V from 1.8V.

We are monitoring these voltages with 5% tolerance using a micro-controller with built-in 10-bit ADC in the design.

We have received the designed PCB recently. Currently we are in testing phase.

During testing, its noticed that on random occasions, micro-controller was reading out of range value for 1V and 1.2V voltages from TPS7A8300RGWT.

Now during investigation to find out the reason, its noticed that when CNR/SS capacitor is touched with oscilloscope probe or touched with finger, regulator output is going out of tolerance consistency. This is happening on both the regulators. I am not sure if this is co-related to random fault from these regulators.

Kindly look into this issue and let me know if there is any fix to this.

  • Hi Waseeq,

    The CNR/SS capacitor is what is generating the reference for the LDO. This is a high impedance node, so if you touch it with your finger or a scope probe it will change the voltage at the NR/SS pin. If you need to monitor this pin you should use a DMM/Oscilloscope that has a 10G ohm impedance to monitor it. This will keep the reference voltage from changing very much.

    Best Regards,
    Mark
  • Hi Mark,

    Thanks for clarifying, however on odd occasions there is some fluctuation at the output voltages without probing or touching, which the micro-controller who is monitoring these voltages is able to capture this variation, This looks strange but Is there anything that would be influencing this. Schematics and TPS7A8300_Schematics.pdfLayout is as per datasheet recommendation. I have attached the schematics, let me know if there is anything I can try out.

  • Hi Waseeq,

    Thanks for the schematic, I don't see any issues with that. When you are able to see a difference in the output of the LDO with the micro-controller how big is it? Do the fluctuations in the output voltage correspond with changes in the input voltage or the output current?

    Another thing you can try is cleaning the board. Sometimes during manufacturing there is solder flux residue that can cause leakage currents that can change the NR/SS voltage.

    Regards,
    Mark
  • Hi Mark,

    Thanks for checking the schematics. There is variation of +/-5% to +/-10% of output voltage. Load current and input voltage are constant. I will check for proper soldering and let you know if this issue persists.

    Regards,

    Waseeq