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TPS3890: TPS389033: Wrong output voltage on RESET

_Lina
Expert 3305 points
Part Number: TPS3890

Team,

We are currently using a TPS389033 in our design as a supervisor for a C2000 device (F28377d) as a part of our reference design. Although the part receives 3.3V into Vdd, and 1.2V into SENSE, it only outputs 2.2V on RESET pin. 

Pull up resistor value is 4.7kOhm on RESET and a cap to ground (0.1uF). The cap on CT is 1000pF, and the cap on the supply is 1uF. It is only one board out of 5 that is showing this behavior. Any thoughts as to what would be causing this or how to debug? 

Best,

  • 0
    TI__Genius 12630 points

    Lina,

    If you look at the EC table 7.5 on pg 5 of the datasheet: http://www.ti.com/lit/ds/symlink/tps3890.pdf you can see the V_IH (High-level output voltage [this should be labeled as V_OH - we will work to fix this]) is 0.7 x Vdd at the min value. This means the lowest the output should be while "high" is 0.7 x 3.3 = 2.31V. Since you are seeing a lower voltage of 2.2V on RESET pin, I believe it is because the resistor pull-up value is not high enough. The datasheet uses 1Mohm in the example application circuit.

    Also, I noticed the CT capacitor value is 1000pF (1nF) but the minimum allowed is 1.149nF (1.5nF if using capacitors with +/- 20% tolerance). This should be followed unless there is a specific reason not too.

    Feel free to reach me at my work email: michaeldesando@ti.com for detailed troubleshooting if increasing the pull-up resistor does not fix this issue.

    -Michael