• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 220 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.

TPS61089: frequency at 1mA

Given Ding
Genius 10125 points
Part Number: TPS61089

Hi Team, 

in customer's application, they use TPS61089 as power supply for audio, then there is above 20kHz ripple requirement. 

In TPS61089, it's PFM mode at light load, so want to check with you on the frequency at below condition: 3~4Vin, 10.5Vout, 1mA load.  

Is the Webench simulation result on PFM mode correct? If so, I can use Webench but since PFM mode is non-linear control, I'm not sure if PFM model match the actual design. Thanks. 

BRs

Given 

  • 0
    TI__Expert 5180 points

    Hi Given,

    I tested required working condition based on TPS61089EVM, the frequency at PSM mode is not fixed and will changed due to noise or interference. The tested frequency is in 16.7-76.9kHz range which may be below 20kHz for short time.

    For such low power PSM mode, I think switching frequency shortly below 20kHz may be acceptable, because the total energy is so small at 10.5mW to be heard.

    Frequency in PSM mode is also depend on Cout because small Cout will accelerate discharge process and increase PSM switching frequency. EVM is 3*22uF//1uF at output. If frequency is strictly required, Cout can be corresponding decreased without affecting normal work such as output ripples.

    Webench is not accurate on PFM mode, because Webench can only simulate for short time. It can simulate normal heavy load condition. Frequency at PFM mode is recommended test through lab.

    Best Regards,

    Eric Yue

  • 0 in reply to Eric Yue
    TI__Genius 10125 points

    Hi Eric, 

    Thanks for your reply. In customer's design, it's 3Vin to 11Vout, Iout=90mA, so I use Webench design, the Cout is only 1x10uf. So it can be above 20kHz, right? Thanks. 

  • 0 in reply to Given Ding
    TI__Expert 5180 points

    Hi Given,

    Typically, three 22-μF ceramic output capacitors work for most applications. 10uF Cout seems too small. I tested frequency through EVM, which has 3*22uF Cout. The frequency is about 467kHz which is similar to Webench design and is above 20kHz.

    Best Regards,

    Eric Yue