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TPS2116: TPS2116 for 1.8V sideband circuit review

Hu David
Prodigy 20 points
Part Number: TPS2116

Hi Sir,

Would you kindly help to review whether below circuit is OK? Thanks!

Description:
1) If only 3.3V exist, Q21 turn off, PR1 is high, V_SW output VIN1, 3.3V
2) If both +3.3V and VIO_1V8 exist, Q21 turn on, PR1 is low, V_SW output VIN2, 1.8V

Regards,

David Hu

  • 0
    TI__Genius 13300 points

    Hello David Hu,

    With your current setup I'm assuming 3.3V for PR1 is same as VIN1 supply? When PR1 is low (Q21 conductive) and VIN1 is high then VIN2 will pass. When PR1 is at 3.3V (Q21 non-conductive) and VIN1 is high then Vout will pass VIN1. When VIN1 is low and PR1 is low (Q21 conductive) it will pass VIN2. PR1 can not be high when VIN1 is low otherwise output will be Hi-Z since MODE is tied to VIN1. 

    Everything looks good; however, I would recommend adding input capacitance onto your 1.8V rail since if it dips below 1.6V during a switchover event it could disable internal protection features. 

    Regards,

    Kalin Burnside

  • 0 in reply to Kalin Burnside
    Prodigy 20 points

    Hi Kalin,

    Thank you very much!

    From the 1.8V Sideband circuit, we need change the connection of VIO_CFG.

    Based on above, I have updated the circuit as below, would you kindly help to double check, thanks!

    (updated the circuit to control the connection of VIO_CFG)

    My  analysis as below:
    Here used PMOS to control the PR1 voltage, VIN1 connect to VIO_1V8, VIN2 connect to +3.3V
    1) If only have +3.3V, Q23 turn off, PR1 is low， V_SW output VIN2, 3.3V.Since PR1 is low, ST will
    keep low. (Internally NMOS turn on?)
    2) If both have +3.3V and VIO_1V8, Q23 turn on, PR1 is high， V_SW output VIN1, 1.8V, this time ST
    will keep High. (Internally NMOS turn off?), maybe we need     keep R252 /R223 NOB here. And
    use the embedded NMOS to control it.

    Pls kindly help to double check, thanks very much!

    Regards,

    David Hu

  • 0 in reply to Kalin Burnside
    Prodigy 20 points

    Hi Kalin,

    For  the input capacitance  you said onto the 1.8V, which value will be better here? how about 1uF or 10uF?

    Regards,

    David Hu

  • 0 in reply to Hu David
    TI__Genius 13300 points

    Hello David,

    1 uF should be fine. 

    How are you turning on/off Q23? Also is R255 intended to be not populated? 

    Regards,

    Kalin Burnside