TPS7A8300: GND issue

Hi ASHU,

Generally LDOs are placed referenced to analog ground as they are power products. This helps to minimize noise to downstream devices. At some point (typically at the load) the analog and digital grounds should be tied together since the LDO and load would otherwise be referenced to different voltages.

Very Respectfully,
Ryan

hi Ryan ,

Thanks for your reply.

I have many LDO and switching regulator in my design. For Each DC-DC , I am using separate analog ground AGND_1, AGND_2 etc. And in the last I am tieing ANG_1 to DGND through 18 ohm ferrite bead.Is it ok ?or i need to have common AGND across the board ?

Thanks
Ashu

one more question I have that how much current rating i need to chose for ferrite bead.
I am deisigning TPS7A8300 for 2A current.



Thanks
Ashu

Hi Ashu,

The LDO will not care how many grounds you have in your system, it will simply regulate with regards to its input and the ground that it is tied to. Your loads may care as there could be an offset in the ground voltages.

With Kirchhoff's laws the ferrite bead needs to be able to handle the current going through the LDO. In your case, since you have 2A going through TPS7A8300 the ferrite bead will also have 2A going through it.

Very Respectfully,
Ryan

Hi Ryan,

Can I share schematic of TPS7A8300 to you for review?

Thanks
Ash

Hi Ash,

Yes, you can insert an image or attach a file to this E2E thread. In general I only need to see the portion around the LDO. Here is more information on how to do this:

e2e.ti.com/.../149.4-3-inserting-an-image-on-e2e

e2e.ti.com/.../148.4-5-attaching-a-file

Very Respectfully,
Ryan

Hi ,

Can u share your e-mail id?

Thanks

Hi Ash,

While we understand the desire of confidentiality, we generally prefer to keep forum threads open in order to leverage the community benefit of learning from a large pool of designers, users, engineers, customers, etc. Many issues can be "scrubbed" of confidential information and still posted with enough information to solve a particular issue. I would imagine this is the case for your schematic review as well since I only need to see the LDO which you already stated is TPS7A8300, the value of the input rail, the value of the output rail, the value of the bias rail (if there is one), and the capacitors/resistors associated with TPS7A8300.

In the event that you need to send a private message please review the following from the Learn E2E Blog:

e2e.ti.com/.../3032.08-adding-friends-sending-private-messages

Very Respectfully,
Ryan