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TPS546D24A: Absolue Max for VOSNS

Wayne Fite50
Prodigy 85 points
Part Number: TPS546D24A

The TPS546D24A supports designs up to 6V in Webench but the datasheet has an Absolute Max of 5.5V for VOSNS.

My design is 5.5V output – Am I operating with no margin to the Abs Max or do I have .5V to work with?

If I divide down Vout with resistors and set the voltage accordingly, I can reduce the voltage on this pin.   Any problems with this approach?

  • 0
    TI__Genius 14455 points

    Hi

      The TPS546D24A is capable of working for a Vout of 5.5V,  So, 5.5V on VOSNS should be ok.

    The WEBENCH design of 6V will need to be updated and we will take care of it.

    Regards,

    Gerold

  • 0 in reply to Gerold Dhanabalan - Online Design Tools
    Prodigy 85 points

    Thank You

    It seems that VOSNS is the only pin really limiting the output to 5.5V.  

    Is it possible to use a divider at Vout for VOSNS if I would like to go above 5.5V output?

  • 0 in reply to Wayne Fite50
    TI__Genius 14455 points

    I will double confirm on that. As the device is expected to work for 5.5V applications, I dont think you will need any divider. One of the experts on this device will respond shortly.

    regards,

    Gerold

  • 0 in reply to Wayne Fite50
    TI__Mastermind 48240 points

     

    The TPS546D24A can support nominal voltages upto 5.5V without risking damage to the VOSNS pin.

    It looks like the Absolute Maximum VOSNS pin voltage needs to be updated.  I can support 6V safely.

    While I would not recommend using an additional feedback divider to reduce the VOSNS pin voltage, it is possible, but there are some things to keep in mind:

    1) Input impedance at the VOSNS pin

    The TPS546D24A includes an internal resister divider from VOSNS to GOSNS that has a nominal 130kOhm resistance (85k - 165k) that will load any external divider that needs to be considered when selecting an external resistance.

    2) VOSNS is the sense voltage for the regulation and read vout values

    The VOUT_COMMAND and READ_VOUT values will be affected by the external divider, regulating or reporting the VOSNS voltage instead of the output voltage unless VOUT_SCALE_LOOP is also updated.  For an output voltage of 5.5V, the internal divider will be set to 8:1 (0.125) if an external divider is also used, the VOUT_SCALE_LOOP will need to be further reduced by dividing by (1+ Rtop/Rbot) from the external resistor to allow the internal digital to compensate for the external divider in VOUT_COMMAND and READ_VOUT functions.

    3) Programmable Range for VOUT_COMMAND is limited to 6V.  To get output voltages greater than 6V, you would need to use an external resistor divider and not correct VOUT_SCALE_LOOP as described in #2, but correct the scaling from VOSNS to VOUT with the host's selection of VOUT_COMMAND and interpretation of READ_VOUT.

  • 0 in reply to Wayne Fite50
    TI__Mastermind 48240 points

     

    One additional consideration.  The TPS546D24A has a 400ns typical, 500ns maximum Minimum Off-time that will limit the duty cycle depending on the switching frequency.  This will also limit the maximum output voltage, depending on the input voltage and switching frequency selected.