TPS54319: tps54319 uvlo resistance

Hi Kingson,

Thank you for your question.

The two formulas should provide similar results, since R2 and RUVLO2 formulas are the same.

Assuming VENA = 1.18V, and multiplying both numerator and denominator of (4) by RUVLO1, you can see that both numerator are something like VENA * R1.

The denominators are slightly more complicated.

Starting from R2 formula, we can write its denominator like (A):

Moving to RUVLO2 denominator (after having multiplied by RUVLO1), you have:

From RUVLO1 formula, you can obtain (B):

And substituting in the previous one

Thus (A) and (B) have the same structure.

Did this clarify your question?

Please ask again if you need further support.

Thanks,

Stefano 

All information in this correspondence and in any related correspondence is provided “as is” and “with all faults”, and is subject to TI’s Important Notice (http://www.ti.com/corp/docs/legal/important-notice.shtml).

Hi Stefano

Referring from the following 6 formulas, I calculate the R1 and R2 again.

When I use formulas (1)(2) or (3)(4), I get the same result that R1=88.23k and R2=36.43k. This is right.

But when I use formulas (5)(6) with the 0.944, I get a result that R1=22.35k and R2=10.30k. These have so much differrences from the above result.

So I wonder, where the 0.944 comes from? And when should we use the 0.944?

Here is my calculation excel for your referrence. thanks for your help.

UVLO_Calculation.xlsx

Hi Kingson,

Thank you for your question.

As a general consideration, you should remember that the two devices are very different; in particular TPS54319 is low voltage device whereas TPS54561 can support up to 60V VIN. This means that, even if this feature is the same, the IC implementation is very different and could lead also to different reference formulas.

Please refer to the specific device datasheet during the design.

I will check internally for more info on the 0.944 factor, but since the device is quite old only little documentation is available.

By the way, are you using it for a new design?

If so, I would advise you to refer to newer alternatives as TPS62826 for a 3A application.

Thanks,

Stefano

All information in this correspondence and in any related correspondence is provided “as is” and “with all faults”, and is subject to TI’s Important Notice (http://www.ti.com/corp/docs/legal/important-notice.shtml).

Hi Stefano

Thanks for your reply.

Please let me know how the 0.944 factor comes from if you have any updates.

Kingson

Hi Kingson,

I will look into it and give you an update by tomorrow.

Thanks,

Stefano

All information in this correspondence and in any related correspondence is provided “as is” and “with all faults”, and is subject to TI’s Important Notice (http://www.ti.com/corp/docs/legal/important-notice.shtml).