TPS82085: TPS82085 - Schematic review

Hi Shlomi,

I would like to point out four different things on your schematic:

- We recommend a total output capacitance value of 150uF max for the TPS82085, It would be beneficial to your system especially at startup to lower the output capacitance. You should then retrieve 2x47 uF  caps per rail.  

- FT4 needs to be placed after the output caps it is really important to have the output caps as close as possible to the IC.

- Regarding the ferrite beads used, they have a 40mOhm DCR resistance. Knowing you want to have 2.65A max at the output current. You will acknowledged a non-negligible voltage drop across it. I would then recommend to have a slightly higher output regulation and then modify the resistor bridge at feedback.

- Depending on what consideration interests you the most between output accuracy and efficiency. I recommend you read this App Note explaining you how to design best your resistor bridge at the feedback pin:  http://www.ti.com/lit/an/slyt469/slyt469.pdf

If you have any other questions please ask.

Thank you!

Best Regards,

Dorian

Hi Shlomi,

I haven't heard back from you. Do you have any further questions on this topic?

Have you made changes to your schematic implementing the feedback I gave you ?

Thank you very much!

Best Regards,

Dorian

Hi Dorian,

1. I can override the F.T component with the R527 if the system noise will be low .
2. The direct output Dc2cde is a capacitor 47uF ceramic (the actual capacitive at 1.8v is about 24uF) .
3. Between DC2dc and capacitor load I have an F.B with a serial resistive of about 40 mill-ohm.Does resistive not it help me?
4. The actual total capacitance summary is ~  5x24uF=120uF.
5. The F.T4 component was inserted into the feedback of DC2dc to offset the serial resistance and reduce output noise. I've done this before with DC2dc of TOREX / T.I and it gave very good results.  

Thanks,

Shlomi

Hello Shlomi,

I am not certain to understand every changes you have made. Can you send back the schematic with the changes?

Thank you very much!

Best Regards,

Dorian 

Hi Dorian,

Attachment new schematic.

Thanks,

Shlomi

TPS82085SIL.docx

Hi Dorian,

1. Plan ig good?
2. Between DC2DC and capacitor load I have an F.B=L1 with a serial resistive of about 40 mill-ohm. Does resistive not it help me?( total output capacitance value of 150uF max).

Thanks,

Shlomi

Hello Shlomi,

When we state in Datasheet 150uF max of output cap, it is for every power line the system is using. So you are fine here!

For the DCR of about 40 mill-ohm of F.B=L1 it is not a problem, you just need to be aware that you will have a voltage drop across it. As mentioned before, you could compensate it by rising the output voltage regulation, if you change the resistor bridge at feedback. 

1. "The F.T4 component was inserted into the feedback of DC2dc to offset the serial resistance and reduce output noise. I've done this before with DC2dc of TOREX / T.I and it gave very good results."  I don't see that on the schematic you sent. If you feel confident using it, it is up to you.

Do you have any further questions?

Thank you!

Best Regards,

Dorian

Sorry

TPS82085S.docx