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TPS54821: How to determine voltage divider resistor values

Naveen Jakka
Prodigy 160 points
Part Number: TPS54821

Hello,

I am trying to find out the values for the resistors in the voltage dividers between V_SEN and PH pins (R1 and R2).

The above diagram is given in page 1 of the datasheet http://www.ti.com/lit/ds/symlink/tps54821.pdf.

As per the given equation 1, which is the resistor R5 and R6 in the above diagram.

Although the equation refers to figure 29, I don't see R5 and R6 labels placed correctly there.

For example, the example in Figure 29, it needs 3.3V output, and applying equation 1 to it, R5 = 10^4(3.3-0.6)/0.6 = 45kOhm, but the figure shows 2.2kOhm resistor.

Could someone please clarify this bit for me, perhaps by revising the equation with respect to the above equation.

My need is to output 12V for which I am needed to find the resistor values.

Thanks,

Naveen.

  • 0
    TI__Guru**** 191445 points

    Navee,

    The various sections in the datasheet are more or less stand alone sections that may use different reference designators for the same components.  I would use the design example in Section 8.2.  The Eq. 29 in Section 8.2.2.9 references the correct reference designators for the schematic in Figure 29.  For 12 V output, if R7 = 190 k, then R8 = 10 k.  You may use different values so long as the ratio remains the same.