EM2130 cannot output expected voltage

[Twincreeks]

Dear support team,

I am using EM2130L/H to generate 0.9 V and 3.3 V for a Cyclone 10 GX FPGA. And I am having some issues.

I have tested two boards. On the first board, EM2130L outputs 0 V, and its 3.3V output of the internal LDO (Pin 16) is 0 V. EM2130H outputs 0.78 V, and its 3.3V output of the internal LDO is 4.3 V. 

On the second board, the output 0.9 V of EM2130L is good, but the 3.3 V output of EM2130H is about 2.04 V. The 3.3V output of the internal LDO (Pin 16) is OK.  

I copied the design of the Cyclone 10 GX Development Kit Board (Schematic available at https://www.intel.com/content/dam/altera-www/global/en_US/support/boards-kits/cyclone10/c10gx-dev-kits-board-a1-release.pdf). I attached the schematic of my design (only EM2130 part).

The CTRL pin of both EM2130L/H is connected to the output of a power sequencing chip (LM3881) and is verified to be high (2.76 V). For EM2130L RTUNE resistor (R55), I do not have a 6.04 kohm resistor, so I use a 6.20 kohm instead. For EM2130H, for the first board, RTUNE is 0.390 kohm, while on the second board, I try 0.390 khm and 0 kohm, but the output is the same (2.04 V). 

I have a few questions.  

• Could you please review my schematic and see if there are any potential issues?
• For EM2130L, I use six tantalum capacitors of 330 uF and three ceramic capacitors of 100 uF, the same as the Development Kit. These capacitors correspond to 1.5 times base capacitance. Per Table 11 of the datasheet, the RTUNE should be 4.220 kohm. However, I don’t understand why the Development Kit chooses 6.04 kohm.
• For EM2130H, I use two tantalum capacitors of 330 uF and seven ceramic capacitors of 100 uF, the same as the Development Kit. However, I cannot find the RTUNE value in Table 12 of the datasheet because Table 12 lists either all ceramic capacitors or polymer aluminum / ceramic capacitors. No tantalum capacitors are listed in Table 12.
• I found a thread in the forum (https://community.intel.com/t5/Intel-Enpirion-Power-Solutions/EM2130L-Start-up-problems/m-p/570606). The support team suggests to use 22 uF to replace 2.2 uF for the decoupling capacitor (C192 and C453). In the same thread, the support team suggests to use 0 ohm to replace the 100 ohm feedback resistors (R368 and R369) and remove the sensing resistors R377 and R378. Could you please confirm these modification are mandatory? If these modifications are mandatory, why is the evaluation kit working properly? It is best to include such information in the datasheet or the development kit schematic so that in the future nobody continue to waste time.

Best regards,

Andy Liu

[Mostafa_Intel_AE]

Hello Andy Liu,

I am sorry for late response.

Since 0.9V design works in one of your board, probably there is no design issue.

It looks the issue maybe be a soldering issue since one of the board shows VDD33 voltage is 4.3V.

Also to confirm if we don't have stability issue, please disable the remote sensing by unmount R60 and R62 and change Rtune to 0R (the loop is not optimized)

Please probe Vout, PVIN, VCC, and CTRL signals of regulator and share the scope waveforms.

If you have the capability to communicate with the regulator using the GUI through the PMBUS, so we can check if there is any fault that triggered during the startup.

Thanks,

Mostafa