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Original question:

TPS61022: TPS61022 current limit at Low Input Voltage.

TPS61022: Question Asking

Jason Ciou
Expert 3600 points
Part Number: TPS61022

Hi team,

My customer has some question about TPS61022, please see below.

1.) For Pin 6, when this pin pull low, the device always work at PWM mode, when this pin pull high, the device will operate PFM mode at light load, but the normal load will operate PWM mode, do I understand right?

2.) Could PFM mode improve the EMI?

3.) I don't not very understand 1.01* Vout_nom, could you give me an example? 

4.) In the shutdown mode, the device is entirely turned off. The output is disconnected from input power supply. which mean there is no leakage current in there right?

Jason

  • 0
    TI__Genius 9046 points

    Hi Jason,

    Please kindly see my comments below. Any questions please let me know. Thanks!

    1.) For Pin 6, when this pin pull low, the device always work at PWM mode, when this pin pull high, the device will operate PFM mode at light load, but the normal load will operate PWM mode, do I understand right?

    [WW]No, your understanding is not right.

    When MODE is pulled low,  Auto-PFM: the device will operate PFM mode at light load, but the normal load will operate PWM mode

    When MODE is pulled high, FPWM: Always PWM whatever light load or heavy load

    2.) Could PFM mode improve the EMI?

    [WW]Not sure about what EMI you are referring to. If you have bad layout, the radiated EMI cannot be improved by PFM. PFM is only used here to improve efficiency. Under PFM, there will be reduced output voltage ripple frequency and increased ripple amplitude than PWM.

    3.) I don't not very understand 1.01* Vout_nom, could you give me an example? 
    '

    [WW]See below: The application note/blog about PFM is planning to publish in 1Q22 soon, to explain mechanism of PFM, which a lot of people are asking now.

    4.) In the shutdown mode, the device is entirely turned off. The output is disconnected from input power supply. which mean there is no leakage current in there right?

    [WW]Please kindly refer to spec in datasheet. 

    -Wenhao

  • 0 in reply to Wenhao Wu
    TI__Expert 3600 points

    Hi Wenhao,

    For 3, do you have an explanation which talking about the work principle?

    For 4, although disconnect the input power supply, there still has  leakage current?

    Jason

  • +1 in reply to Jason Ciou
    TI__Genius 9046 points

    Hi Jason,

    For 3, do you have an explanation which talking about the work principle?

    Refer to below description in the app note. 

    "

    Figure 1 illustrates a simplified mechanism of PFM (Pulse Frequency Modulation) which has been used in TPS61022. PFM is one kind of PSM and helps increase light load efficiency. TPS61022 utilizes adaptive constant on-time valley current control. As which can be seen, initially output current drops, as a result, output voltage rises. Internal error amplifier decreases inductor valley current to response increased output voltage. However, when inductor valley current drops to low clamp, error amp is clamped and inductor valley current does not drop further.

    As the error amp is clamped, there is always energy larger than load demanded sourcing to output side. Therefore, output voltage keeps increasing. When FB hits PFM reference, internal comparator sets both FETs to be OFF after rising delay TDLY_R. When FB drops below PFM reference, comparator releases both FETs after falling delay TDLY_F. After that, the clamped EA ramps inductor valley to the low clamp and output voltage increases. The delay is not intentionally designed and is unnecessarily considered in real design. Output ripple in PFM has been simulated across corner cases to be 30mV(typ.) and 50mV(max) under datasheet’s recommended operating conditions.

    "

    For 4, although disconnect the input power supply, there still has  leakage current?

    Yes, when VIN=0V and VOUT=5.5V. please refer to datasheet spec.

    -Wenhao

  • 0 in reply to Wenhao Wu
    TI__Expert 3600 points

    Hi Wenhao,

    Thanks.

    Could you send the APP note to me?

    I'd like to know more about this control method, I don't send to customer.

    Jason

  • 0 in reply to Jason Ciou
    TI__Genius 9046 points

    Hi Jason,

    Sorry, this app note is still pending publishing, and cannot be shared out.

    -Wenhao

  • 0 in reply to Wenhao Wu
    TI__Expert 3600 points

    Hi Wenhao,

    I got it, thanks.

    Jason