Hello,
I have two questions - one which is related specifically to the TPS54527, and the other more general.
1. In the TPS54527 datasheet, under the "Typical Application" section, there is a 10K resistor connected to the EN pin. Why is that? What is the rationale behind this?
2. For example in the TPS748, under the "Application Information" section, there is a table, listing different output voltages and corresponding configuration resistor values. However - in some cases, the theoretical value of the output voltage one gets from calculating using the 0.8*(1+(R1/R2)) formula deviates from the stated output voltage in the table. This deviation is, however, very small. What is puzzling though, is that "perfect" voltage is achievable using common resistors. For example:
- The table states, for example, the following resistor combination for 1.2V output - R1=2.49K R2=4.99K. Calculating using the formula yields 1.1975....V output. ~2.5mV deviation.
- But, it is possible, while using "Standard 1% Resistor Values", to get exactly 1.2V using R1=1.1K and R2=2.2K. These even are more "common" resistors, much more available if you are a hobbyist. These resistors are still fulfilling the R2 smaller than 4.99K suggestion in the datasheet(if smaller currents required, 1.8K and 3.6K also work).
This phenomenon is seen across many datasheets in similar sections, across different manufacturers and different parts. It seem that there is some advantage in using E96 resistors even if the configuration is slightly off, while the E24 series gives perfect results(and are widely available in 1% tolerances).
Now, i am a novice, and it seems i am missing something that is perhaps obvious to anyone in the industry dealing with such components - why most datasheets recommend using values that yield an imprecise voltage, while more common, more precise resistors are available?
Thank you,
Shay
