VREF is a low-power reference voltage equal to half of VDDQ. It must also be equal to VTT ± 40 mV. The following figure shows the VREF generation circuit.
Figure 1. VREF Generation
The following are the guidelines for connecting VREF power:
- For light loads (less than four DDR components), connect VDDQ to VSSQ through a simple resistor divider composed of two equivalent 1% 1 kΩ resistors.
- Generate a local VREF at every device, rather than generating a single VREF with one divider and routing it from the controller to the memory devices.
Decouple at each device or connector to minimize noise.
Note: Use discrete resistors, not a resistor
pack, to generate VREF.