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Original question:

TPS543C20: Setting the output voltage

TPS543C20: How to set VSEL

Lauren Mayfield
Expert 6910 points
Part Number: TPS543C20

I have a question regarding VSEL. Since it sets the initial power on voltage, should it be set to the operating output voltage? For example, if your output voltage is 0.85V but the VSEL resistor is 0 Ohms, so the initial power up voltage is 0.6V. 

  • 0
    TI__Expert 5310 points

    Hello,

    The resistance between the VSEL pin and AGND sets the internal reference voltage. If RSP and RSN are tied directly to VOUT and GND of the output respectively, then the VSEL voltage will determine the power up voltage as you mentioned. If you want the output voltage to power up to a different value than the VSEL voltage, then a resistor divider is needed from Vout->RSP->RSN such that the voltage seen between RSP and RSN is equal to the voltage set by VSEL.

    For example, if a 0 ohm resistor is selected for the VSEL pin, this sets the internal reference voltage to 0.6V. In order to achieve 0.85V at the output in this case, a resistor divider is needed such that the voltage between the RSP/RSN pins is equal to 0.6V. This can be achieved by connecting a 4.17kohm resistor from VOUT to RSP and a 10kohm resistor from RSP to RSN. This divider circuit presents a fraction of the output voltage (10/14.7) to the RSP pin (RSN being tied to the GND reference). 0.6V is equal to (0.85 * (10/14.7)).

    If the output voltage is equal to one of the VSEL options in the end application using the TPS543C20, I do recommend setting VOUT=VSEL. However, this is not necessary as the resistor divider may set an output different than VSEL.

    Regards,

    Alec Biesterfeld