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TPS65140: Adjusting the Vo4 to 3V6

Raphael Marchi
Intellectual 1260 points
Part Number: TPS65140
Other Parts Discussed in Thread: TPS65100

 

Hello, Team

 I am working to replace MAX1531ET by TPS65140PWPR in a Infotaiment system.

 

This will drive a 7” TFT bipolar display , that requires the following voltages:

+16V, -7V, 10.4V and 3.6V typ

 

Looking at TPS65140 datasheet, I saw that the Vo4 is internally adjustated to generate 3.3V by two resistors. I would like to put an external resistor to adjust the linear output to  3.6V.

 

Questions:

 

  • Do you see any problem in that implementation?

  • What are the two internal FB resistors values, so we can try to set an external resistor to re-adjust the voltage? attached image extracted from datasheet.

 

Your quick return is appreciated, once I will test this w our EVM

 

  • TI__Guru 58215 points

    Hello Raphael,.

    The resistor divider values are 96k for the one from reference to GND and 163.7k for the one from FB4 to reference. But the accuracy of resistors in silicon is very process dependent. The proportion of the resistors will stay the same, but the value varies in the range of 20% or so.

    Therefore I cannot recommend adding a series resistor from VOUT4 to FB4.

    In addition there is some more circuitry from FB4 to BASE which most probable makes this anyhow impossible. I did not test it on the bench up to now, but from the design it does not look promising.

    Best regards,
    Brigitte

  • in reply to Brigitte
    TI__Guru 58215 points
    Hello Raphael,

    One more comment:
    If the 3.6V supply is for the VCOM of the panel, I recommend using TPS65100 instead of TPS65140 because this has an integrated VCOM buffer. The advantage of using a VCOM buffer for the VCOM voltage is the fast reaction time on current spikes which are happening on VCOM normally.

    If the 3.3V regulator on TPS65100 is not needed, please disable it by connecting ENR to GND. It is a good practice to connect BASE and FB4 to VIN.

    Best regards,
    Brigitte