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TPS61378-Q1: switching between Forced PWM and Auto PFM modes

Part Number: TPS61378-Q1
Other Parts Discussed in Thread: TPS63020

Hello, we are going to use both of Auto PFM and Forced PWM modes of TPS61378-Q1.

I can't find any description in datasheet on how to switch between these two modes correctly.

Have we to take a special care of EN pin, or something else, when we need to go from PFM mode to PWM and vice versa?

Or we can just change a logical level on MODE/SYNC any time we need a mode change?

Thank you.

  • Hi Slavia,

    You can find the description in Table 6-1 Mode selection pin. MODE = high, forced PWM mode. MODE = low or floating, auto PFM mode.

    What do you mean you are going to use both of auto PFM and forced PWM mode? I don't get your point.

  • Hi Zack,

    The idea is to increase the overall efficiency. 

    When our system does not require high amount of current, we put all of the ICs into sleep mode and want to put TPS61378 into Auto PFM mode to decrease the self consumption of this IC.

    If system decides, that more current is needed by load, TPS61378 has to be switched to PWM mode.

    So we want to cyclically change the control mode of TPS61378 depending on required output current.

    The question was: is such kind of application is allowable for TPS61378, and do we need to pay extra attention to something else when changing the mode?

  • Hi Slava,

    You can connect MODE pin to GND to set TPS61378-Q1 working at Auto PFM mode.

    In light load conditions, the device works at PFM mode with high efficiency.

    In heavy load, the device will automatically changes to PWM mode.

  • Hello Zack,

    Constant using of Auto PFM mode is not always good for us, because we need a low noise level on Vout, even if load is not heavy.

    We have a negative previous experience with using PFM mode on TPS63020. The Vout noise level for this device in PFM mode was higher than in PWM mode. This factor leaded to erroneous data from GPS-module powered from TPS63020 in PFM-mode.

    We suppose to use:
    - to have a clean Vout for GPS module - PWM mode,
    - to save power when device sleeps -PFM mode.

    We want to make a selection of PWM or PFM mode by changing the logic level on MODE/SYNC pin, without turning the TPS61378 off .

    So the question is: is such kind of changing the mode of TPS61378  allowable?
    Will TPS61378 work correctly in this case? Do we need to remove Vin of TPS61378 prior to change the MODE/SYNC state?

  • Hi Slava,

    Understood. A lot of devices output voltage ripple in PFM would be larger than PWM mode.

    You can change the logic level on MODE pin without turning the device off.