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Altera_Forum's avatar
Altera_Forum
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10 years ago

DDR2 VREF problem

Hi, My FPGA design uses 4 ddr2 devices. And I use LP2996 to output VTT and VREF for FPGA and DDR2. However, VREF measures 1.43V other than 0.9V. After I cut the VREF output trace, I found LP299...
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
10 years ago

Check that you're not exceeding the current capacity of the vref output. The rating on the regulator is probably very low and the total current draw on the FPGA could be higher.

Also if the pins are dual function then be sure to make the assignment. The default is usually input with weak pullup which would inject vddq into the vref through a resistor.

Finally check that there are not any shorts between vref and vddq.