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WEBENCH® Tools/TLV62568PEVM-860: 3.3V Regulator Output too Low

N S
Intellectual 365 points
Part Number: TLV62568PEVM-860
Other Parts Discussed in Thread: TLV62568

Tool/software: WEBENCH® Design Tools

Dear Support

I used Webench to enter the following:

Vin Min = 3.5V

Vin Max= 4.2V

Output: 3.3V @ 1A @ 60'C

It gave me few options and I selected the one with TLV62568

I ordered the evaluation boards TLV62568P-EVM-860

I changed the feedback resistor R1 to 453K (0603)

I changed the Inductor to 1uH from Farnell-2289185

https://uk.farnell.com/coilcraft/xfl3012-102meb/inductor-1uh-2-6a-20-pwr-115mhz/dp/2289185?ost=2289185&krypto=Yq58RD63%2FtpwWNhcJoVKCcwXLeihlTg3gS%2FuJjs5oQyrhNy%2FTCuqMHDsrHFHClXOZ9wMHLBGIYUYZx168dhIyA%3D%3D&ddkey=https%3Aen-GB%2FElement14_United_Kingdom%2Fsearch

I removed the default output cap of 10uF & replaced with two 22uF caps (0805) in parallel from Farnell:

https://uk.farnell.com/tdk/c2012x5r1a226k125ab/cap-22-f-10v-10-x5r-0805/dp/2346921?ost=2346921&ddkey=https%3Aen-GB%2FElement14_United_Kingdom%2Fsearch

I measured the cap values before fitting using my Fluke 117, & they were apprx 22.2uF each

I used 3.6V/0.4A bench power supply to power the EVM & the output is apprx 3.2V. instead of 3.3V

Initially, I had only 10uF cap  & the output was apprx 1.7V with 453K feedback

So, I changed to 2 x 22uF & still it was less than required target of 3.3V

I then added 3rd cap of 10uF so all together 2 x 22uF + 1 x 10uF but the output voltage dropped below to 3.0V.

I am getting worried now if this is suitable for my application as at the moment I am using this without any load (i.e., its output is not connected to my circuitry which has opamps  & other ICs who have standard 1uF + 100nF across them Rail decoupling caps (quite few of them) & if this regulator has such negative effect on its output by adding caps (whilst no load is connect then would it really work in actual application?

Why am I not getting the desired 3.3V output?

I have tried by connecting a 750R 0603 load across the output to see if adding load helps in improving the situation but still no luck.

Any suggestions?

  • 0
    TI__Mastermind 36631 points
    Dear Customer,

    Is the output dropped below regulation at 1A load only or even at no load?

    One option you can try is to use an inductor with higher Isat (ex. XFL4020-102ME; Isat =4.5A). It is possible that at 1A load that the high side FET reached that ILIM (1.5A, minimum) limiting the duty cycle which in effect will reduce the output voltage.


    Best regards,
    Excel
  • 0 in reply to Excel Regidor
    Intellectual 365 points
    Dear Excel
    Thanks for getting back to me.
    No the output has no load connected and it is still dropped below target 3.3V.

    And if I connect a load of 750R which is again well below the target of 1A, it still doesn't make any difference.


    I take your point for isat of inductor but so far it has never been used for 1A load

    Kind regards
    NS
  • 0 in reply to Excel Regidor
    Intellectual 365 points

    Dear Excel

    Further to my last message, I have also tried 2.2uH inductor that comes with the Evaluation Kit (rated @ 2.8A). But I see the same problem.

    And again my load was no where near 1A. I used 750R resistor across the output.

    I am desperately looking for solution to this problem as I was expecting the voltage regulation to give me least of problems. I designed my board originally with SOT23-5 LDO but that seems to struggle. It looks like that with LDOs TPS73201 & TPS73633, my output goes to dead short circuit after working fine for few minutes. I used Ceramic X5R/X7R caps (tried combination of 10uF / 1uF & 100nF) separate & together (both @ inputs & outputs). I also tried 47uF tantalum (both at input & output) but they for some reasons they go dead short circuit. And if I take the caps OFF board & then put back same caps (with the same LDO), the short circuit disappears.

    I powered the same circuit (load) with bench top power supply set to 3.3V current limited to 0.4A and my current consumption never goes higher than 25mA. So, both of the LDOs should have worked.

    Then I thought may be its my layout (as I am restricted with space on  my board) So, I decided to order this Evaluation Kit for 1A switch mode & now this is struggling even in isolation (i.e., with my actual circuit load connected to it)

    Looking forward to hearing from you

    Kind Regards

    NS

  • 0 in reply to N S
    TI__Mastermind 36631 points
    Dear NS,

    Please provide the schematic diagram and layout related to TLV62568P. If you can provide the whole schematic of your board the better.

    I suggest to isolate the circuit related to TLV62568P. Don't put a supply to other part of the circuit.
    Supply TLV62568P with 5.0V at no load. If it is not regulating properly, check the FB pin. It should be 0.6V.
    If not then replace TLV62568P with new sample. Then measure again the output.

    Let me know the test results.


    Best regards,
    Excel
  • 0 in reply to Excel Regidor
    TI__Mastermind 36631 points

    Dear NS,

    I will temporarily close this trend. Once you have the data, you can open it again by responding to it and I will reply to it immediately.

    Thank you.


    Best regards,
    Excel

  • 0 in reply to Excel Regidor
    Intellectual 365 points
    Dear Excel
    Could I have your email please so I could send my schematic & layout files to you.

    Kind Regards
    NS
  • 0 in reply to N S
    TI__Mastermind 36631 points

    Hi NS,

    This is my email add: e-regidor@ti.com.


    Best regards,
    Excel