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TPS61222: Minimum output current for proper voltage regulation

Chundra Ramful1
Prodigy 250 points
Part Number: TPS61222

Hi,

I plan to use the TPS61222 in an energy harvesting application that requires a 5V rail with an extremely low power consumption.  The 5V rail will be used to drive a CMOS based analog switch whose input will be ~5V.  The current used by such a device is not constant and probably hovering close to a few nA.

I selected the TPS61222 because of its very low Iq.  My question is whether it will be able to provide a 5V regulated output under almost no load.

Chundra

  • 0
    TI__Mastermind 21565 points

    Hi Chundra:

    If there is no load, the converter will operate at PFM. The Vout will be a little larger than the target. 

  • 0 in reply to Minqiu Xie
    Prodigy 250 points

    Hi Minqui,

    Could you please clarify what PFM stands for?

  • 0 in reply to Chundra Ramful1
    Prodigy 250 points

    Hi Minqui,

    I would like to use the TPS610997 instead of the TPS61222.  Could you confirm if this is a better device for my application?  Also, I eventually found out that PFM = Pulse Frequency Modulation.

    Section 7.5 of the TPS610997 data sheet mentions that in PFM mode regulation will typically produce 5.15V instead of 5.00V.  However, I could not find any place in the data sheet which explicitly states that the converter is stable with no load.  Could you please confirm if this is indeed the case or if should allow for a bleed current?  If required, what is the minimum bleed current value?

    Chundra

  • 0 in reply to Chundra Ramful1
    TI__Mastermind 21565 points

    Hi Chundra:

    Sorry that I didn't explain it clearly. Yes, the PFM is pulse Frequency Modulation. That's a kind of power save mode to increase the efficiency during the light load. And it can stop the reverse current in most devices.

    The device can be stable both with or without the load. The only difference is it regulate the Vout in PFM is littler higher that normal PWM. 

    I don't have a clear number for when to go into the PFM, as it's related to Vin, Vout, Inductance and other factors. (Generally, <10mA it will operate in PFM, >100mA it will operate in PWM. Just some typical case for your refer.)