Hi,
I have been developing an ADC board based on the design of Xilinx ML605 demo board. The power supply circuit is also nearly the same as ML605 using 2 UCD9240 with 5 PTD08A020W and 2 PTD08A015W.
I have made 3 prototype units. I found that the PMBUS of UCD9240 of the last prototype board lost link with “USB interface adapter” in some situations while the other two prototypes function normally.
The following testing steps would cause problem arose in the last unit:
Case 1 (function normally)
The testing steps:
- Set the Xilinx V6 as JTAG configuration mode
- Powered up the circuit
- Started the “Fusion Design Online” software with “TI USB interface adapter” connected to BMBUS interface
- The software could recognise the 2 UCD9240.
- Downloaded the FPGA program to the V6
- The power regulators worked well and the PC could keep monitoring all the power module status
Case 2 (lost link)
The testing steps:
- Set the Xilinx V6 as master configuration mode
- Powered up the circuit
- The V6 FPGA auto configured
- Started the “Fusion Design Online” software and the phrase “No Device Found” was shown on the screen while the PowerGood LED was on
- I have checked the voltage output of each power module and all is normal including 1V, 1.2V, 2.5V, etc.
Observation:
- It seems that the UCD9240 is still running except the PMBUS interface
- The PMBUS_data pin is always low while the PMBUS_clk pin is always high
- The voltage of BPCap pin is around 1.75V
I guess the UCD9240 POR circuit and FPGA startup current (noise) might cause the failure of the PMBUS interface. I’m still figuring out why there is a problem found in the last prototype unit while the other unit can function well (suppose the three units should have the same circuit and PCB layout).
Any suggestions on hardware or UCD9240 setting modification?
Besides, I found that the UCD9240 pin48 (#TRST) in ML605 circuit is always pull high, but in TI spec., this pin should be pull low. Which one is correct?
Please help and thanks!
Louis