Hi All,

Page 13 of the datasheet for the TPS55340 Regulator (datasheet also attached below) contains the following schematics of a 12V to 24V boost circuit:



I'd like to build this circuit, however, I can't quite understand the function of 2 resistors, specifically: R5 & R6 (circled in the above pic).

Regarding R6 - it is marked as having an 0R value (this value appears both in the schematics & in the BOM of the evaluation board for this IC which I'll discuss momentarily Hence I don't think the value is a mistake).

Now I've seen cases where an 0R resistor was used as a jumper to facilitate difficult routing, but it doesn't seem to be the case here. One of the evaluation boards for this IC - TPS55350EVM-017 - consists of exactly this circuit (see datasheet here, and also attached below). Here's a pic of the board's layout with R6 circled in both images (page 13 of the datasheet):



As you can see, there doesn't seem to be any trace running under R6 or suchlike, so I'm guessing it's not a jumper.

My second guess is that R6 forms part of an RC network when interacting with C7 (a 0.1uF cap connected directly below it). But if R6's value is 0R how can it make any difference/do any work in this context? Is it just a matter of the value not being actually 0R but representing some marginal resistance?

So my first question is: Given that R6's value is 0R, what is it doing in the circuit? What function does it serve?

Btw, the evaluation board's BOM (page 16), lists R6 as "Resistor, chip, 1/16W, 1%" in a 0603 package, if it helps.

Moving on to the second resistor R5 (also circled in the attached schematics above).

R5 is valued at 50R and it's connected in series with a 187K resistor (R1), so I assume its only function is to serve as the top part of a voltage-divider for the test point to which the 2 resistors are connected (TP2 LOOP).

So my second question is: Assuming I don't need/want a test point in my circuit, can I safely dispose of R5?

Thank you very much in advance,
SnowCrash

 

Hi again,

As there were no replies forthcoming in this forum, I tried my luck with Texas Instruments themselves. It took them a bit of time, but eventually they got back to me and I figured I'll post their response here in case it might help someone in the future:

"Usually we recommend a small resistor for R6 for filtering. If the input is free of noise, this resistor can be eliminated. Anyway, it is just a good practice but not very critical.

Regarding R5, its main purpose is for loop measurement. It is the place where you inject the perturbation and measure the open loop property."

 

You can omit R6 if you don't need a test point, 50 ohms won't alter the output voltage much.

 

You can omit R6 if you don't need a test point, 50 ohms won't alter the output voltage much.

Cool, thanks Dodgydave!