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TPS61022: What are the function of high-side switch？

Stanley Xu
Intellectual 1810 points
Part Number: TPS61022
Other Parts Discussed in Thread: TPS56C215, TPS546C23, TPS546D24

1.Refer to datasheet I wonder what is the purpose of high-side  switch is designed to be able to transfer between NOMS and PMOS？

2.For most  synchronize boost why choose PMOS as high-side switch but NMOS ？

at buck and boost application, what's the difference between PMOS and NMOS?

 What should we consider when designing a switch inside the boost or buck converter？

  • 0
    TI__Genius 9046 points

    Hi Stanley,

    This HSFET is always a PMOS. Choosing the PMOS is because we have this craft for LV converters and we are able to control the direction of body diode. However, for higher voltage we do not have this craft and NMOS is still needed to be used.

    For buck converter or boost converter, we specifically choose the die size for a given MOS craft. Design will do a lot of simulations to ensure the FETs with proper Rdson is chosen to give converter best efficiency over working conditions.

    For example, buck converters like TPS546C23, TPS546D24 or TPS56C215, is designed specified for low duty cycle, high output current condition, so LSFET needs to have lower Rdson. HSFET sometimes needs to have higher BVDSS (break down voltage) than LSFET in consideration of higher input voltage range. Thanks!

    -Wenhao

  • 0 in reply to Wenhao Wu
    TI__Intellectual 1810 points

    What is the purpose of controlling the direction of the body diode? The block diagram shown above PMOS does not have a body diode. It should be for real load disconnection, right?

  • 0 in reply to Stanley Xu
    TI__Genius 9046 points

    Hi Stanley,

    Yes, for load disconnection function. The block diagram is for understanding. You can see there is a switching across FETs.

    -Wenhao

  • 0 in reply to Wenhao Wu
    TI__Intellectual 1810 points

    Hi Wenhao,

    thank you for kindly answer, one remaining question is that why you mentioned This HSFET is always a PMOS", low cost? easy

     to open?

  • 0 in reply to Stanley Xu
    TI__Genius 9046 points

    Hi Stanley,

    For the device I support now is LV-boost. And most of them HSFET is PMOS. Using PMOS stands for our craft advantage to control the body diode thus we have true shut down mode when there is no Vin, or EN is low. For other devices the HSFET could still be NMOS, like mid-high voltage boost or buck-boost. Thanks!

    -Wenhao