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TPS61023EVM-052: Light load operation

Michiaki Tanii
Expert 4650 points
Part Number: TPS61023EVM-052
Other Parts Discussed in Thread: TPS61023

Hello team,

 

Customer test TPS61023 with our EVM in the below condition

 

<Conditions>

Vin : 2.7V

Vout : 3.293V

R3 = 680kohm, R4 = 150k ohm (in the EVM)

 

<Test results>

- Vout : 3.41V        Iout = 0mA

- Vout : 3.38V        Iout = 100mA

- Vout : 3.36V        Iout = 200mA

- Vout : 3.32V        Iout = 300mA

- Vout : 3.31V        Iout = 400mA

- Vout : 3.32V        Iout = 500mA

 

As the above, in the current more than 300mA, the output voltage is stable but there is large variation of Vout at less than 200mA.

I think that one of the reason is that TPS61023 would enter PWM mode but I would like to know the reason why there is large variation.

 

And also could you advise the threshold to enter PFM mode ?

 

Thank you and best regards,

Michiaki

  • 0
    TI__Mastermind 34231 points

    Hi Michiaki,

    The TPS61023 integrates a power-save mode with PFM to improve efficiency at light load. When the load current decreases, the inductor valley current set by the output of the error amplifier no longer regulates the output voltage. When the inductor valley current hits the low limit, the output voltage exceeds the setting voltage as the load current decreases further. When the FB voltage hits the PFM reference voltage, the TPS61023 goes into the power-save mode.

    A easy way to calculate the threshold of entering PFM mode is see when inductor current is no long CCM mode any more.

    In PFM mode, the reference voltage rises to 0.601V from 0.595V(PWM mode) so output voltage is normally 1% higher than PWM mode output voltage.

  • 0 in reply to Zack Liu
    TI__Expert 4650 points

    Hello Zack,

     

    Why the variation of output voltage is seen between no load and Iout = 200mA ?

    Could you kindly advise the reason ?

     

    You mentioned the way to calculate the threshold of entering PFM mode but it means that TPS61023 doesn’t have specification of threshold entering into PFM mode ?

     

    Thank you and best regards,

    Michiaki

  • 0 in reply to Michiaki Tanii
    TI__Mastermind 34231 points

    Hi Michiaki,

    In PFM mode, the reference voltage is 601mV. In PWM mode, the reference voltage is 595mV. 

    The threshold of entering into PFM mode is FB voltage hits the  PFM reference voltage and inductor valley current hits the low limit.

  • 0 in reply to Zack Liu
    TI__Expert 4650 points

    Hello Zack,

     

    I understand what you mean but could you give us more detail why the output voltage variation is seen between Iout = 0mA and Iout = 200mA even if reference voltage at the FB would be same at typ 601mV ?

    - Vout : 3.41V        Iout = 0mA

    - Vout : 3.38V        Iout = 100mA

    - Vout : 3.36V        Iout = 200mA

    Thank you and best regards,

    Michiaki

  • 0 in reply to Michiaki Tanii
    TI__Mastermind 34231 points

    Hi Michiaki,

    May I know how did you measure the output voltage? Are you measuring the Vout_sense pins because the power cables also have voltage drop.