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TPSI31PXQ1EVM: TPSI31PXQ1EVM

Mohamed Sadek Rechid
Prodigy 10 points
Part Number: TPSI31PXQ1EVM

Tool/software:

Hello , 

Dear TI support team , I started testing the TPSI31PXQ1EVM evaluation module using low HV input ( 30Volts) to become familiar with the board before going to higher voltages , when i probed V_capacitor (  i used 0.47uF) i observed an exponential curve , however in the datasheet i expected to see a linear ramp since the avg current from the inductor is constant  . 

  1. Why do i see an exponential curve instead  of ramp ? 
  2. how should i measuring the charging current ( i assume this the same current passing through the shunt resistor   or somewhere else ?

thank you for your support ! 

  • 0
    TI__Expert 7286 points

    Hello Mohamed,

    Thanks for joining E2E and reaching out to our team!

    The EVM by default has 125 mohm shunt resistor, so the comparator is looking for 9.84A before turning off the MOSFET. Since the voltage and capacitance is quite low, the current is likely not reaching the 9.84 A before the capacitor is fully charged. Try increasing your voltage and capacitance or increase shunt resistance in order to see the linear charge.

    If you want to stay with 30 V and 470 nF, try using Rshunt = 4.3 kohm. This should charge in about 100 ms.

    For measuring output current, I typically use current probe clamped on output cable. Current passing through shunt resistor works too.

    Best regards, 
    Tilden Chen

    Solid State Relays | Applications Engineer

  • 0 in reply to Tilden Chen
    Prodigy 10 points

    Hello Tilden,

    Thank you very much for your clear explanation     , I wanted to mention that during my testing, the original shunt resistor (R1, 0.15 Ω, 2 W, 2512 package) on the board was damaged. In the lab, I only had the same value  resistor available but with a 1 W power rating instead of 2 W.

    Do you think it is acceptable to use this 1 W version for   tests (e.g., 30 V – 400 V), or would this risk further damage due to power dissipation, especially when I move towards higher voltage tests (up to 400 V in my case)?

    Thanks again for your guidance and support!

    Best regards,
    Mohamed

  • +1 in reply to Mohamed Sadek Rechid
    TI__Expert 7286 points

    Hello Mohamed,

    Thanks for your reply.

    1W is fine, the time is extremely short. These resistors typically have an overload rating, 5x for 5s. Meaning resistor rated for 1W at DC may be able to handle 5W if the load time < 5s. Just allow for adequate cooling time in-between precharges.

    Best regards, 
    Tilden Chen

    Solid State Relays | Applications Engineer