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TPSI31PXQ1EVM: Active Precharge

Suraj Singh
Prodigy 30 points
Part Number: TPSI31PXQ1EVM

Tool/software:

Dear TI Support Team,

I hope this message finds you well.

I am currently evaluating the TPSI31PXQ1EVM for a pre-charge application and would like to confirm a few details:

1. Voltage Support: Can TPSI31PXQ1EVM reliably support for input voltage of 1000V?

2. DC link Parameter: This application involves DC link capacitor of 2500uF, targeting a pre-charge duration approximately 2 seconds, could you please confirm if TPSI31PXQ1EVM is suitable for this configuration?

3. Pre-Charge Time Setting: While referring to the calculation sheet provided on the product page, I have noticed that it does not allow me to manually set or select the required pre-charge time. Kindly advise how this value be configured or if an updated tool is available.

reference: (https://www.ti.com/tool/TPSI31PXQ1EVM)

4. Could you also please provide application note on component selection and calculation.

Best Regards,

Suraj Singh

  • +1
    TI__Expert 7356 points

    Hello Suraj,

    Thanks for joining E2E and reaching out to our team!

    Suraj Singh said:
    1. Voltage Support: Can TPSI31PXQ1EVM reliably support for input voltage of 1000V?

    Yes, the components in the design are minimum rated for 1200-V.

    Suraj Singh said:
    2. DC link Parameter: This application involves DC link capacitor of 2500uF, targeting a pre-charge duration approximately 2 seconds, could you please confirm if TPSI31PXQ1EVM is suitable for this configuration?

    Yes, the EVM targets 4-5 A average charging current, so it would charge 2.5 mF to 1000 kV in around 423 ms. 

    Suraj Singh said:
    3. Pre-Charge Time Setting: While referring to the calculation sheet provided on the product page, I have noticed that it does not allow me to manually set or select the required pre-charge time. Kindly advise how this value be configured or if an updated tool is available.

    The calculation sheet outputs charge time (tCHARGE), which is mostly a function of inputs sense resistance (RSENSE) and inductance (L). So you can modify RSENSE and L if you desire a different charge time. For your application, I'd recommend RSENSE = 300 mΩ and L ≥ 300 µH.

    Suraj Singh said:
    4. Could you also please provide application note on component selection and calculation.

    We are working on a design guide, plan to release by end of July. 

    Best regards, 
    Tilden Chen

    Solid State Relays | Applications Engineer

  • 0 in reply to Tilden Chen
    Prodigy 30 points

    Thank you Tilden Chen!

    I would like to understand the following -

    1.how pre-charge time is calculated for the TPSI31PXQ1EVM? Is the calculated Precharge time same for both TPSI31PXQ1EVM with Psupport (TPSI305x-Q1) and without Psupport. 

    2.Could you please share the formula or methode used for determining the pre-charge duration based on the system parameters.

    3.Relation between Inductor and Rsense vs Precharge Time: Could you please explain how the inductor and Rsensor resistor influence the pre-charge time? 
       I'm particularly interested in understanding how changes in these components affect the charging profile of the DC link capacitor.

    4. Impact of increasing Rsense Resistance: If we increase the resistance of the Rsense resistor, does this pose any thermal risks to the circuit or the resistor itself? is there a recommended range or power rating for Rsense to safely handle such adjustments without overheating? 

  • 0 in reply to Suraj Singh
    TI__Expert 7356 points

    Hello Suraj,

    Thanks for your reply.

    Suraj Singh said:
    1.how pre-charge time is calculated for the TPSI31PXQ1EVM? Is the calculated Precharge time same for both TPSI31PXQ1EVM with Psupport (TPSI305x-Q1) and without Psupport. 

    Psupport just adds additional switching power. So if your calculated inputs do not exceed TPSI31P1 switching power limit (42 mW), then enabling Psupport does not improve charge time. To estimate precharge time, you can follow the example in my following answer. The calculator does it a little differently by summing the charge accumulated per switching cycle (Q = It) until VLINK reaches VBAT.

    Suraj Singh said:
    2.Could you please share the formula or methode used for determining the pre-charge duration based on the system parameters.

    To estimate charge time, first we find the peak and minimum current thresholds and average them to find the average charging current. Then I can use the average charging current to solve for charge time, given voltage and capacitance since I=Q/t. 

    For example, if I select Rsense = 125 mΩ, Ipeak = 1.23 V / 125 mΩ = 9.84 A, Imin = 0.160 V / 125 mΩ = 1.28 A, so Iavg = 5.56 A. We can calculate charge time with t = Q/I and Q = CV. Assuming 2 mF capacitance to 800 V, this would be t = 800 V * 2 mF / 5.56 A = 287 ms. 

    You can see the TIDA 060063 design guide for more details on the operation theory while we work on a design guide for this as it is very similar.

    Suraj Singh said:
    3.Relation between Inductor and Rsense vs Precharge Time: Could you please explain how the inductor and Rsensor resistor influence the pre-charge time? 
       I'm particularly interested in understanding how changes in these components affect the charging profile of the DC link capacitor.

    You can try using the calculator and inputting different Rsense and L values to see how they affect the charge time, but basically Rsense modifies the average charging current, while L affects the current slope (di/dt). So bigger Rsense lowers average current which increases charge time. Larger L, decreases di/dt, which decreases switching frequency (i.e. switching power), but can increase charge time a bit.

    Suraj Singh said:
    4. Impact of increasing Rsense Resistance: If we increase the resistance of the Rsense resistor, does this pose any thermal risks to the circuit or the resistor itself? is there a recommended range or power rating for Rsense to safely handle such adjustments without overheating? 

    We intentionally selected resistors with overload rating (5x for 5s), meaning that a resistor rated for 2W at DC can handle up to 10W for 5s. Since precharge tends to be <1s, thermals won't be much of an issue. Definitely need to consider thermals for long precharge times or multiple consecutive precharges (turning vehicle on off repeatedly). 

    Best regards, 
    Tilden Chen

    Solid State Relays | Applications Engineer

  • 0 in reply to Tilden Chen
    Prodigy 30 points

    I need one more clarification regarding the TPSI31PXQ1EVM module

    what should be done with Pin 13 (VDDH) and Pin 14 (VDDM)?

    Should these pins be left unconnected, or do they need to be tied to specific voltages for proper operations?

  • 0 in reply to Suraj Singh
    TI__Expert 7356 points

    Hello Suraj,

    Thanks for your reply.

    Since TPSI31P1 integrates isolated power, you can leave VDDH and VDDM floating while using the EVM.

    Best regards, 
    Tilden Chen

    Solid State Relays | Applications Engineer