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PMICLOADBOARDEVM: Load board setup and debug

Vinod Narayan
Prodigy 10 points
Part Number: PMICLOADBOARDEVM

Tool/software:

Hi Team,

My name is Vinod and I work at Meta in the hardware engineering team. I am working on bringing up the PMIC load board that we are planning to use for testing our PMIC. There are a couple of issues we are running into, if you can please help with explanation/debugging that would be great. Just so you know, I tried asking this question in the E2E forum but it is not letting me post my question. I have attached images of the setup, the setup is as follows:

1. 50mV control signal pulse, frequency - 1 Hz is being configured from AWG and connected to J1, the switch is set to the right position to enable parallel mode

2. A Keithley SMU is connected as a source (set to 1.5V) to measure current and is connected to Load1 and GND

3. Another Keithley SMU is connected to Ch1, J2 to measure voltage. Also, the scope probe is connected to the same leads to observe the time domain voltage waveform

4. The current probe is connected to load1 and gnd to observe the current waveform on the scope

5. The power supply is configured to +11 and -11 volts as recommended and connected to J5 power terminal. 

Issues: 

Issue #1:

As you can see the waveform, the voltage waveform (J2 output - Color yellow) and Current waveform (Blue Color) it has a weird step to it and it also seems to be periodic, almost a step-down ramp of equal to 100mA which is significant.  We are trying to debug and trying to explain the possible reasons, have you seen something like this on your setup and can you help us with the reason and/or debug? Let me know if you have further technical questions or if it is possible to schedule a virtual call?

Issue #2:

If we compare the rise time of the voltage waveform (yellow) and rise time of the current waveform (blue color) there seems to be a significant difference. If we zoom in, we can confirm that the rise time of the "voltage" waveform is close to 200ns but if we look at the "current" waveform the rise time is close to 3us. In the setup guide you show the rise time to be as fast as 80ns for current that goes from 0-8A. We have a current probe that is capable of measuring ns time and we have extremely small leads on the pads, i even tried reducing the length thinking that is contributing to the delay but no change in the current waveform. Can you please check and also let me know about this?

Please let me know, I would greatly appreciate your response ASAP. 

Thanks and Regards,

Vinod

  • 0
    TI__Expert 6440 points

    Hi Vinod,

    Issue 1. 

    I don't recall seeing this kind of behavior. Load board is sensitive to load cable lengths but this should be seen as oscillation. 

    Is input signal from AWG 50ohm matched?

    Issue 2.

    For this I suspect SMU cannot provide high enough current. Meaning fast transient including cables will limit transient current from SMU very much, typically range is microseconds for ~10' cables, and to really be able to measure faster transient you would need to add cap very close to load board connector, around inch or two maximum. 

    Also to note that user's guide figure is measured with EVM where there is hundreds of microfarads caps on EVM side and very short loop. And current waveform is taken using on board current sense resistor, measured voltage over and translated to current.

    Faster the transient more all parasitics comes to play in real application. I think you are seeing some symptoms because of those. 

    There is experiment of integrating this same design on bottom side of the EVM to further reduce parasitics and we were able to achieve range of ~10ns rise/fall times for 0-12A load. 

    Br, Jari