1.8.2 VREF Power

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 1-15. 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.

Important: Use discrete resistors, not a resistor pack, to generate VREF.