TPS57114-Q1: Question about the position of the sense resistor in relation to the regulator's feedback loop

Hello Giulio,

I want to make sure I understand your system right.

Can you share a schematic of what you are trying to achieve?

Thank you.

Regards,

Dorian

Hello Dorian,

thanks for your fast reply.

Please give a look at the pictures below with options 1 and 2.

Case 2 should guarantee the regulation at the load (node B) with less ripple.

thanks

G

Hello Giulio,

Unfortunately I cannot see the picture, I send you a request to have a private conversation.

Once you accept I will come back to you as soon as possible.

Thanks a lot!

Regards,

Dorian 

Hello Giulio,

I didn't hear back from you.

Could you upload the same image somehow differently, to make sure I understand your question?

Or can you accept friendship request, so we can discuss via private message?

Thanks a lot!

Regards,
Dorian

Ciao Dorian

Sorry I somehow missed the previous messages because I had other inquiry with your forum.

I will try to send back the picture (I did not realize that it wasn't sent correctly) and yes, I am pleased to accept your friendship request..

Buongiorno Giulio,

In general to avoid noise on the feedback trace from affecting the feedback loop, we recommend to keep Vsense connections short and directly connected at a stable voltage which is the output capacitor. You can also refer to the layout example we have in the datasheet (section 10.2).

What you can do to compensate the Rsense drop knowing you are using an adjustable R2, is to aim for a slightly higher regulation point.

Let me know if you have any other queries.

Thanks a lot!

Regards,
Dorian

Hello,

the problem is that the load current is not constant and with very big variations. moving the feedback point downstream the RSENSE allows the regulator to set an higher voltage, very fast,  in response to the resistor's voltage drop. Hence the output resistor seen from the voltage loop is divided by the feedback factor.

all of this happens very fast , especially if we set an higher regulator's switching frequency, the R2 adjustment process is very slow compared to the feedback adjustment.

Basically what I see in simulation is that after the kick related to the fast load transient the voltage is set to the desired value.

Plus this might be beneficial because, with the proper layout, we can set the feedback tap directly on the device's supply pin.

Regards,

G.

Hello Giulio,

I understand more challenges you are facing here.

My concern here as Vsense will be routed further away from output capacitor is that it would add inductive path in the feedback loop and might alter compensation speed and accuracy.

I think if special attention is brought to Layout to make sure Rsense is not too far away from output capacitor nor on the other side of the board, this should be fine. Do you have a layout, you could share here?

Thank you very much!

Regards,

Dorian 

Thanks Dorian,

Unfortunately I don't have any layout to share at this time, but what I can say is that both Regulator and Sensing resistor will be placed as close as possible to the rail, after the sense, the proper rail filtering will be implemented, so I can't see any serious issues.

Do you have any layout guidelines to share?

We are also exploiting, for the most demanding rail, a fast conversion with the MCU's internal (and very fast) ADC fed by your INA301. Max current is around 15A.

Do you have any guidelines/suggestion for this component or maybe can you suggest something different?

Simulations with your spice models are already satisfactory ( 10mOhm sense + INA301A1).

Best regards,

G

Thank you Dorian,

your feedback was very valuable and the layout example is crystal clear!

Please proceed with the INA301. I got several questions to ask :-)

best Regards,

G