• State TI Thinks Resolved
  • Locked Locked
  • Replies 9 replies
  • Answers 4 answers
  • Subscribers 63 subscribers
  • Views 226 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

TPS65919-Q1: SMPS1 Maximum Current drawn

Art Mecina
Genius 16505 points
Part Number: TPS65919-Q1

Hello Guys,

Good day.

Our customer is using O919A152TRGZRQ1 in automotive ECU application. The output voltage of  SMPS1 is 0.8V. They would like to know how much maximum current they can draw from SMPS1 with 0.8V voltage output.

In datasheet, output voltage range specified is "0.7- to 3.3-V " with 3.5 Amp current . Please clarify along with Impact, if any, on other outputs on device.

Thanks!

Art

  • 0
    TI__Mastermind 24740 points

    Hello,

    The efficiency, at 0.8V output and 3.5A load current, is around 60%. The power losses is around 1.86W due to SMPS1 rail. Junction to ambient thermal resistance is 24.8C/W. The 3.5A load at 0.8V causes junction temperature rising of 1.86W*24.8C/W = 46.3C.

    Regards

  • 0 in reply to Mahmoud Harmouch
    TI__Genius 16505 points

    Hello Mahmoud,

    Thanks for looking into this!

    However, customer have some clarifications below.

    They would like to know how much maximum current can be drawn from SMPS1 if they configure it for 0.8V output. Reference Calculation : 3.3V*3.5Amp=11.55W (max power delivery as per SMPS1 specification) so if they configure device for 0.8V and considering maximum power 11.55W, calculation (11.55W/0.8V=14.4 Amp)says they can draw 14.4 Amp maximum output current.

    Hence, they want this calculation be checked and confirm how much maximum current they can really draw from SMPS1 for 0.8V output voltage.

    I will direct customer to this thread, so that they would be able to explain their use case better.

    Thanks!

    Art

  • 0 in reply to Art Mecina
    TI__Mastermind 24740 points

    Hello Art,

    The output current relative to output voltage is not linear. The power losses is higher at lower output voltage and same current. Please check the efficiency plots below. Your statement is right by theory and with neglected power losses. At 3.5A load current, the efficiency is 90% at 3.3V but it only around 60% at 0.8V. I hope this explains the issue and please let me know for further question.

    Regards

  • 0 in reply to Mahmoud Harmouch
    TI__Genius 16505 points

    Hello Mahmoud,

    Thanks for the clarification. You mentioned something about the efficiency plots. I don't see any. Maybe i missed it?

    Best regards,

    Art

  • 0 in reply to Art Mecina
    TI__Mastermind 24740 points

    Hello Art, I thought I inserted the picture.

    Regards

  • 0 in reply to Mahmoud Harmouch
    TI__Genius 16505 points

    No worries Mahmoud. Thanks!

    Art

  • 0 in reply to Art Mecina
    TI__Mastermind 24740 points

    Hello,

    I believe the problem is solved and I'm closing this thread. Please let me know for further support.

    Regards

  • 0 in reply to Mahmoud Harmouch
    TI__Genius 16505 points

    Hello Mahmoud,

    Apologies, for the delayed response for I was awaiting the customers' response.

    Please let us know SMPS (out of four) they can use with 3.5A output current @ 0.8V output voltage, with high efficiency. Kindly share the details.

    Thanks!

    Art

  • 0 in reply to Art Mecina
    TI__Mastermind 24740 points

    Hello Art,

    The SMPS 1, 2, or 3 output can deliver up to 3.5A. At 0.8V and 3.5A, the Output Power is 2.8Watts. The power losses in the device is Output Power*(1/Efficiency - 1). The power losses in this rail is 0.8Watts*(1/0.65 -1) = 2.68Watts. The junction to ambient temperature is 24.8C/W. The junction temperature rise above ambient is 2.68W*24.8C/W = 66.5 degrees. The junction temperature max is 125C. That means the ambient should be below 125 - 66.5 = 59 degrees.

    In addition we need to count the power losses due to others rails. Each rail power losses can be calculated the same way.

    As a result the device can deliver 3.5A but the thermal should be considered. The junction to ambient thermal resistance can be lowered by adding an adequate heat sink.

    I hope that answers your question. Please let me know for further support.

    Regards