VDDCI Rail on Polaris GPUs

Here you'll learn about VDDCI voltage rail on Polaris GPUs. How it works, what it is used for, and common issues with it.

The Controller Circuit
Depending on the Vcore PWM controller, VDDCI is either created by the same Vcore controller (in the case of NCP81022 or UP9505P) or a dedicated regulator like GS7250 (incomplete datasheet) or similar buck converter.

PGOOD for VDDCI is mostly not used for anything. VCC, depending on the controller, either comes from the 5V rail or 12v through a resistor. Enable comes from the POK signal from the Display Rail controller, which goes to an NPN transistor which shorts another NPN transistor that is shorting the enable signal as shown in figure 3. Markings on the schematic and board could differ from GPU model to another but the circuit is almost always the same.

Usage
VDDCI is the I/O bus voltage for the card. Used exclusively inside the core.

No VDDCI voltage
Start by measuring the EN and VCC pins of the controller, if one of them is missing, the controller will not operate. If they are both high, check if the FB circuit is as it should be as shown in figure 2.

If everything seems fine but VDDCI is still missing that could signal a dead MOSFET. MOSFETs tend to short when they fail but sometimes they can just stop working without shorting. This can be confirmed if you have an oscilloscope, simply measure the gate of the MOSFET or the "UGATE" pin of the controller to see if the controller does actually create the PWM signal or not. If not, then the controller is likely dead.

After confirming the above is working but there still no VDDCI, this could signal a shorted VDDCI.

In cases where VDDCI is created by the Vcore controller, Vcore would also be missing. Do the above but for the Vcore controller.

Short on VDDCI
If you get less than 5 Ohms on VDDCI it's most likely a dead core. There is a chance that it is a capacitor though, apply isopropyl alcohol on the caps and inject 0.9V to VDDCI and see if any of the VDDCI caps heat up.