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TPS54335A/max duty

Tsukui Yusuke
Guru 21930 points
Other Parts Discussed in Thread: TPS54335A

Hi,

Could you tell me about TPS54335A max duty?

Customer want to know the minimum on time of TPS54335A.
Because there is a possibility that the input voltage comes down.

When the input and output voltage difference is small,
What will happen to this device?

A person with a question there were past. But there is no answer.
Could you tell me your advice?



Best Regards,
Yusuke

  • 0
    Guru 21930 points

    Hi,

    Can I get the information?
    If you need more information or if  I should  clarify my comment ,
    please let me know.
     
    Best Regards,
    Yusuke/Japan Disty

  • 0 in reply to Tsukui Yusuke
    TI__Guru**** 191445 points
    There is no minimum off time requirement for TPS54335A. See SH 6 of the datasheet Switching Requirements. As long as the BOOT to SW voltage is above around 2.1 V, the high side FET can remain on indefinitely. For practical circuits, the BOOT charge will eventually fall below the BOOT UVLO and the high side will turn off and the low side will turn on long enough to re-charge the BOOT cap. So TPS54335A can operate with low headroom between Vin and Vout.
  • 0 in reply to JohnTucker
    Guru 21930 points

    John-san,

    Thank you for your kind support.
    Does this device is 100% Duty can operate?

    Customer condition is:
    Vin=12V to 24V,Vout=12V
    (Customer is concerned about the operation at the time of Vin=12V / Vout=12V condition.)

    If you can not be recommended, are there any other device?

    Best Regards,
    Yusuke/Japan Disty

  • 0 in reply to Tsukui Yusuke
    TI__Guru**** 191445 points
    It cannot do true 100% duty cycle (pass thru). It can do very near 100% duty cycle. The high side FET can remain on past the normal switching period, so it is essentially 100% duty cycle for several cycles, then one very high duty cycle with a short off time to allow the BOOT cap to re-charge. Is this clear?
  • 0 in reply to JohnTucker
    TI__Prodigy 460 points

    John,

    Without extra power circuit which supply boot-cap voltage above SW node, how can I calculate the maximum duty?

    Customer made 5V 3A output with TPS54335A and input voltage could be low as low as 6.6V. 

    So inquired that guaranteed minimum input voltage which could make 5V, 3A

    Please let me know the minimum input voltage for that output power-rail (if it could be varied by switching frequency, then please let me know how can I calculate or example frequency vs input voltage)

    Thank you

  • 0 in reply to Hayden Shin
    TI__Guru**** 191445 points
    Minimum Vin of 6.6 V and 5 V output results in approximately 76 % duty cycle. That is not close to the minimum voltage required to regulate the output to 5 V. I have set the responsible organization to BSR-MCP. That team can provide direct support.