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TPS61086 No Load at forced PWM Mode

tateo yamashiro
Guru 10890 points
Other Parts Discussed in Thread: TPS61086

Hi,

My customer has question about TPS61086.
Could you tell me about questoin?

[Question]
 My customer checked SW pin wave form at EVM under the following condition.

  Vin=3.7V
  Vout=10.2V
  Iout=no load
  L=4.7uH
  MODE pin: pull up to Vin

 Please show this wave form. SW pin wave form is pulse skipping. Why does this device become pulse skipping?

Best Regards,
tateo

  • 0
    TI__Mastermind 40080 points
    Hi Tateo,When TPS61086 work in force PWM mode:
    If the Vin is constant, just change Io, off-time keeps constant, on-time automatically regulates with the load. Operation frequency will be slightly changed, heavy load has lower frequency while light load has higher frequency.
    But when the load current is small , it will still enter into PFM mode.
    Best regards,Helen
  • 0 in reply to Helen chen
    Guru 10890 points

    Thank you for your reply.

    In this case, TPS61086 is forced PWM Mode(MODE pin is pull up to VIN). Why does the device become PFM Mode at very light load? Please explain more detail.

    Best Regards,

    tateo

  • 0 in reply to tateo yamashiro
    TI__Mastermind 40080 points
    The device has a 100ns-150ns minimum on time, in the very light load or no load condition, the output voltage will be higher than the setting voltage if it still work under the PWM mode.
    So the device is designed to work in the PFM mode under the light load to noload condition even the MODE pin is pull up to VIN, thus the output voltage keeps regulate.
    Regards.Helen