• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 38 subscribers
  • Views 506 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.

TPS54160A - Maximum Switching Frequency Data Sheet vs Webench.

Kurt Schmidt
Genius 11125 points

Please see the following post in Non-isolated DC-DC (https://e2e.ti.com/support/power_management/non-isolated_dcdc/f/196/t/558274) Why does Webench limit the maximum switching frequency to well below what the data sheet says it can be? Is this a Webench bug?

"I was attempting to verify a customer design using the TPS54160A for Vin = 9V - 60V and Vout = 5V @ 600mA max. Equations 12 and 13 in the data sheet give me a max switching frequency in the area of 744kHz - 881kHz (they designed for 550kHz nominal). But when we use Webench as a comparison for this design it says the switching frequency cannot be higher than 345kHz.

Why? What are we missing? Is this a Webench bug? By chance does Webench use some very high value for minimum controllable on-time that represents an abs max (the data sheet just says 130ns typ with no maximum given)? Something else I may be overlooking here?"

  • 0
    TI__Mastermind 26740 points

    Kurt,

    Thanks for the question. WEBENCH is also using eq. 12 and 13 from the datasheet. Min controllable on-time is 130ns as well. The major difference is the assumption in the DCR of the inductor and diode voltage drop. We are using 10mohm DCR and 300mV diode drop as compared to 100mohm DCR and 500mV in the datasheet. This is more conservative as compared to the datasheet leading to lower frequencies. The problem we are facing is that we have to select a frequency assuming the parasitics and then design the inductor based on the frequency chosen. We do not know the final DCR till we select the inductor. So, after the inductor selection is completed and if the inductor DCR is lower than the assumption (let's say less than 100mohm as in the datasheet), then the actual shift frequency might be lower than what you designed for. That is one reason we have a conservative estimate on the DCR.

    However, in order to make sure the frequency is not too conservative, I will update the WEBENCH assumptions based on the datasheet and release the changes. That should allow for higher frequencies. I will let you know once done.

    Regards,

    Amod

  • 0 in reply to Amod Vaze
    TI__Genius 11125 points
    Thanks for the rapid response Amod. I understand the issue.

    If you are updating the parameters in Webench we may also want to wait include an update to: a) Ton(max) from Ton(typ) of 130ns - this will tend to drive the max frequency back down, and b) the max allowable input current on the EN pin and how it drives the selection of the UVLO resistors at higher Vin's. I will send you information on this second issue but it will take me at least a day to get around to it due to work load. Are you okay waiting a day or two before updating?
  • 0 in reply to Kurt Schmidt
    TI__Mastermind 26740 points
    Sure, Kurt. I will try to procure max min on-time for this device and try the updates on the frequency selection locally. Let me know when you have the updates on the UVLO resistor selection.

    Regards,
    Amod