topic Re: i.mx6D VDDARM23_CAP Grounding in i.MX Processors

i.mx6D VDDARM23_CAP Grounding

ottawa-imx6 — Thu, 13 Mar 2014 16:44:08 GMT

Hello,

We are currently working on a i.mx6D custom board and have come across a very strange issue.

Perhaps someone who is using this processor can shed some light.

In all documentation we have seen, it is suggested to bridge VDDARM23_CAP to ground when using the DUAL version of the i.mx6 processor (i.mx6D).

Upon initial board bring-up we found that the processor power usage and temperature are unstable and very high. With R23 in place, the processor uses double the power and reaches the trip temperatures within a minute with no load.

It was determined that only by removing the suggested ground connection (by removing R23 in the attached schematic) could the processor stabilize and reach a useable state. This is in conflict with the suggested layout for the i.mx6D.

Currently running 2GB ddr31600.

Does anyone have any experience with this issue?

I am working on optimizing temperature and power usage. Can anyone clarify how they are using the DUAL processor?

Thanks

Brent

Re: i.mx6D VDDARM23_CAP Grounding

JorgeRama_rezRi — Thu, 13 Mar 2014 18:11:15 GMT

Hi Brent,

How is your VDDARM23_IN connection? Are you grounding it too?

Best regards.

Jorge.

Re: i.mx6D VDDARM23_CAP Grounding

ottawa-imx6 — Thu, 13 Mar 2014 18:20:46 GMT

No, it is connected to VDD core.

Is this wrong?

Thanks Jorge.

Brent

Re: i.mx6D VDDARM23_CAP Grounding

ottawa-imx6 — Thu, 13 Mar 2014 18:23:09 GMT

Here we can see the way I have it setup.

Thanks!

Re: i.mx6D VDDARM23_CAP Grounding

JorgeRama_rezRi — Thu, 13 Mar 2014 22:33:44 GMT

Hi Brent,

For dual operation you should ground the VDDARM23_IN pins too. Here's the thing: There's an internal LDO from VDDARM23_IN to VDDARM23_CAP which supplies the i.MX6 core. If you supply the VDDARM23_IN pins and ground VDDARM23_CAP, then there will be current flowing from 23_IN to 23_CAP, that's why your current consumption increases. The ideal way to go would be to ground the 23_IN pins. If this is not possible, you can only leave the 23_CAP pins floating by removing both R23 and R24 and your current consumption will decrease.

Best regards.

Jorge.

Re: i.mx6D VDDARM23_CAP Grounding

ottawa-imx6 — Fri, 14 Mar 2014 19:16:42 GMT

That is clearly what the issue was in my case and it explains it. Thank you.
It would explain why I needed to remove R23 on my schematic..

IF (in my case) R23 is disconnected (floating), and VDDARM23_IN is connected to power (pcb trace that I cannot remove), am I still drawing small amounts of current? Or am I best to modify the pcb to ground both the input and output of VDDARM23 and 23CAP.

I am thinking we will re-do the pcb anyway, but I am curious if it will have any effect.

Thanks!

Brent

Re: i.mx6D VDDARM23_CAP Grounding

rikw_ — Sat, 15 Mar 2014 17:35:47 GMT

I'm glad you found this issue before I finished my PCB. Since floating inputs are generally a bad idea, it seems like the best solution would be to add another zero ohm removable bridge between VDDCORE and VDDARM23_IN on the left-hand side of the schematic. That's what I'm going to do.

Re: i.mx6D VDDARM23_CAP Grounding

ottawa-imx6 — Sun, 16 Mar 2014 23:29:35 GMT

I am glad that we were able bring up a discussion point at least.

None of the demo boards or sample schematics show VDDARM23_IN floating or grounded, so we found out the hard way.

Since we are not using cores 2&3 I think the best solution is to tie both IN and CAP rails to ground (as opposed to the input to VDDCORE which is how it is now with cap floating).

We will tie both VDDARM23_IN and CAP to ground with a zero ohm and I will post my results back here.

Cheers

Brent

Re: i.mx6D VDDARM23_CAP Grounding

sreekn — Mon, 17 Mar 2014 09:09:58 GMT

There is an application note from Freescale AN4397.pdf, regarding common hardware for all 4 versions of processors. The All in one circuit, is as shown below, for the power section.

                                                       Figure 1. All-In-One circuit
Table 4. VDDARMxx_xx Power Connections
          i.MX 6Quad      i.MX 6Dual      i.MX 6DualLite           i.MX 6Solo
SH1     Shorted              Open                Shorted                  Shorted
SH2     Shorted              Open                Shorted                  Shorted
R1         Open                Shorted            Open                      Open
R2         Open                Shorted            Open                      Open

Re: i.mx6D VDDARM23_CAP Grounding

ottawa-imx6 — Thu, 20 Mar 2014 16:57:56 GMT

Thanks everyone for your input!

Problem solved!

Brent