• State
  • Locked Locked
  • Replies 3 replies
  • Subscribers 63 subscribers
  • Views 254 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS2121: PR1 Fluctuation

GP
Prodigy 20 points
Part Number: TPS2121

Hello,

Does anyone have an idea as to why the PR1 signal on my prototype PCB is fluctuating as shown in the oscilloscope image below? This is happening on many samples, but not all. I've also included the schematic portion showing the voltage divider. My hysteresis resistor is set to 71.5 kOhm.

  • 0
    TI__Mastermind 28090 points

    Hi GP,

    What is the IN1 typical voltage?

    Can you send a waveform with this issue that shows IN1, PR1, OUT, and ST?

    Thanks,

    Patrick

  • 0 in reply to Patrick Shalton
    Prodigy 20 points

    Hi Patrick,

    Unfortunately, my scope is only 2-channel, so I had to take the captures separately. 

    Image 1: blue is ST and yellow is PR1.

    Image 2: blue is input 1 and yellow is PR1.

    Image 3: blue is input 1 and yellow is output (exactly overlapping).

  • 0 in reply to GP
    TI__Mastermind 28090 points

    Hi GP,

    It looks like the device is frequently switching between IN1 and IN2. Perhaps the PR1 and CP2 steady state values are very close to each other? Can you send the CP2 side of the schematic too - and I am guessing that BAT1+ = BAT2+ = 4.2V?

    My other instinct is that it could be a soldering issue, but that is ruled out as you mentioned that this takes place on numerous boards. I calculate that with VBAT1+ = 4.2V, PR1 should be at 2.34V, but it looks to be less than 1V while IN1 is active.

    Thanks,

    Patrick