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TPS650250 Resistor Divider for DCDCs

Gus Martinez
Mastermind 28901 points
Other Parts Discussed in Thread: TPS650250

The TPS650250 data sheet states:

When a resistor divider is connected to DEFDCDC1 or DEFDCDC2, the output voltage can be set from 0.6V up
to the input voltage Vbat. The total resistance (R1+R2) of the voltage divider should be kept in the 1MΩ range in
order to maintain a high efficiency at light load. 

However, the app note "Powering the AM335x With the TPS650250" gives a reference schematic with R1+R2<<1MOhm.  

www.ti.com/lit/ug/slvu731a/slvu731a.pdf‎ (page 4).

Should R1+R2 be adjusted in a customer design to meet the data sheet requirement?


  • 0
    TI__Genius 16870 points

    Hi Gus, 

    The app note shows resistor dividers in the range of 100k's which will be fine for the FB resistor divider. Keeping your resistors high is to reduce power loss like the DS states. This power loss can be calculated as follows: Ploss = (Vout*Vout)/(R1+R2). As you can do the math the difference in the losses is in the order of 10's of uW, "pretty low". However, if you design with too high of resistors you can experience output accuracy losses. There are app notes that goes more into detail and explain why and how one should select there resistor divider. Check these app note out below. 

    http://www.ti.com/lit/an/slva450a/slva450a.pdf

    http://www.ti.com/lit/an/slyt469/slyt469.pdf