TPS62085: Whether the VOS Pin can be floated

Hi Varun,

About TPS62085 PG pin must be pulled to output with 1M? Would 100K be all right? Thank you!
BRs

Rannie 

Hi Varun,

Could you please help to review below sch?

If the PG Pin is not used, is that ok to let it NC?

BRs,

Rannie

Hi Varun,

I use the webench to calculate the resistor divider:

3.3V output:

1.2V output:

Is that OK?

BRs,

Rannie

Hi Rannie,

That looks alright to me.

Best regards,

Varun

Hi Varun,

Thanks for your reply.

Correct the sch: L4 should connected to DGND: There is a line between DGND and L4. Should the L4 be removed in this case?

BRs,

Rannie

Hi Rannie,

Ok. I would still recommend to remove it as it still reduces the effectiveness of C273.

Best regards,

Varun

Hi Varun,

Could you please help to draw the sch with figure to elaborate how removing L4. Should C273 connect to AGND or DGND? 

And could you please help to elaborate why L4 reduce the effectiveness of C273 but L6 not influence?

BRs,

Rannie

Hi Varun,

"+3_3VA" is used to power analog signals such as operational amplifiers, and is separated from the digital power GND by magnetic beads (L4 and L6) to avoid interference. Do you think the L4 should be moved?

BRs,

Rannie

Hi Rannie,

Typically there is only one GND (PGND) used for power. So my recommendation is to use a single GND on the output of TPS62085 even after the filters. The currents through the filters on the output of TPS62085 still has to return to the GND pin of the TPS62085 to complete the path.

If the opamp inputs requires a separate AGND, I would suggest checking with the opamp team regarding this and where the AGND and PGND needs to be tied together (my guess is at the GND pin of the opamp )

In the schematic L4 is in series with C273. A capacitor provides a low impedance path to GND for high frequency signals, whereas an inductor provides a high impedance path to GND for high frequency signals. Adding an inductor between the capacitor and GND will increase the impedance for high frequency signals flowing from capacitor to GND. This will reduce the effectiveness of C273.

L6 is not between the capacitor and GND. It is in series with the TPS62805 and the load (opamp). Since the inductor has high impedance at high frequencies it will block the high frequency on this path.

Best regards,

Varun

HI Varun,

Thanks for your reply and Webex call!

Per talked, below sch should be right. I have no more question and thanks again for your support.

BRs,

Rannie