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TPS659037 / Minimum off time of SMPS

S.Satoshi
Guru 21685 points
Other Parts Discussed in Thread: TPS659037

Hi,

I understand that the SMPS9 of TPS659037 output 3.3V, then I'd like to know the minimum input voltage to regulate 3.3V. An minimum off time is necessary to calculate minimum input voltage, but it's not specified in electrical characteristics. Can you provide minimum off time or recommended minimum input voltage to regulate 3.3V?

Best Regards,

Sonoki / Japan Disty

  • 0
    TI__Genius 16410 points
    Sonoki-san,

    Let me look in to this. Typically we've used 5V in with 3.3V out, and we've done 4.2V in to 3.3V out before. I'm not sure if we have the minimum, but let me try to find it.

    Regards,
    Karl
  • 0 in reply to Karl Wallinger
    Guru 21685 points

    Hi Karl,

    Thank you for your support. Please let me know if you can find any information to estimate minimum input voltage.

    Best Regards,

    Sonoki

  • 0 in reply to S.Satoshi
    TI__Genius 16410 points
    Hello Sonoki-san,

    With decreasing input voltage, each SMPS will skip some off pulses in order to increase the duty cycle to keep the regulated output voltage. So it will regulate to 3.3V until Vin is decreased enough so that the SMPS operates in 100% duty cycle. In 100% duty cycle mode:

    Vout = Vin - I*(Rdson + Rl + Rp)

    Where Rdson is the resistance of the high-side FET, Rl is the resistance of the inductor, and Rp is the parasitic resistance, including bond wires, PCB trace, etc.

    We can say Rdson + Rp for the PMIC will be 200mOhm maximum across temp. You should add to this the DCR of the inductor you are using. Since SMPS9 can supply 1A, the maximum voltage drop will be 1A * (200mOhm + Rl). If this is 50mOhm for your inductor, then you should plan for a dropout of 250mV, or 3.3V+0.25V = 3.55V minimum Vin.

    Regards,
    Karl
  • 0 in reply to Karl Wallinger
    Guru 21685 points

    Hi Karl,

    Thank you for your information. I understand that TPS659037 can operate with 100% duty cycle mode. This is enough information.

    Best Regards,

    Sonoki

  • 0 in reply to S.Satoshi
    Intellectual 980 points
    Hi Karl,

    I understand that pulse skipping can also occur if the minimum on time of the SMPS is not met. Can you tell me what is the minimum T_on for the PMIC SMPS?

    Regards,
    Prachi
  • 0 in reply to prachi panse1
    TI__Genius 16410 points
    Hi Prachi,

    We don't spec minimum on time, but we guarantee 5.25Vin / 0.7Vout operation, so the minimum on time must be less than 50ns.

    Regards,
    Karl