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Original question:

TPS62136: Power supply oscillating

WEBENCH® Tools/TPS62136: Switching frequency - different from data sheet.

Elder Costa17
Expert 2825 points
Part Number: TPS62136
Other Parts Discussed in Thread: TINA-TI, TPS62135,

Tool/software: WEBENCH® Design Tools

While I was analyzing the power supply design to stabilize it, I notice the frequency was much lower than expected. I thought it had something to do with my changes, the bulky LC filter on the output so I tried the same design on Webench and the working frequency is close to what I obtained with TINA, ~550kHz whereas the DS states 1MHz.

Unfortunately I could not export the design to TINA-TI (at the moment the server is returning an error: "ERROR: Failed Sim Export Web Service: Connection error"). So I eliminated components from the schematics I was simulating to make it similar to the originally exported by Webench and the frequency is still close to those 550kHz.

The eSIM report shows ~760kHz, clearly wrong when compared with Webench graph.

While writing this I also noticed that this low frequency happens for the 10V version of the supply. On a version with 7.5V ouput the switching frequency is ~1.05MHz on Webench and 950kHz on TINA - different but at least close to the expected.

So, what is the cause of these discrepancies? Does this part change switching frequency depending on output voltage?

Bellow, a link to the Webench design I created to check this issue. I am also attaching the cleaned up TINA file from a previous design with output voltage set to 10V.

1832.Fonte +VAMP-10V-2.TSC

https://webench.ti.com/appinfo/webench/scripts/SDP.cgi?ID=56DA5F0E705FB3DD

  • 0
    TI__Guru**** 150830 points
    Hi Elder,

    I'm not able to follow all your combinations and settings of Vin, Vout, load, and MODE but yes the frequency can vary. Please see this app note, found on the product page, www.ti.com/.../slyt646.pdf.

    Setting MODE high forces PWM mode, which eliminates the lower frequency caused by skipping pulses in PFM mode.

    As well, we have the higher frequency TPS62135. This one also disables the AEE feature in forced PWM mode, for the highest frequency.

    Each D/S has measured graphs of the switching frequency. This is figure 66 and following for TPS62136.
  • 0 in reply to Chris Glaser
    Expert 2825 points
    Hi, Chris,

    Thank you very much for the heads up. I made some assumptions that were clearly wrong regarding the switching frequency. I am more comfortable with the results now.

    Thanks very much for the great support.

    Elder.