Memory Interface Routing Guidelines
80
Design Guide
6.9
DDR Reference Voltage
The DDR system memory reference voltage (VREF) is used by the DRAM devices and the MCH
to determine the logic level being driven on the data, strobe, and control signals. VREF of the
receiving device must track changes in VTT to maximize DDR interface margin. If a voltage
regulator is used, it must reference VTT (See
). If a local resistor divider is used, VREF
and VTT must have a common source voltage between them (i.e., both VREF and VTT are derived
from the same voltage plane), and 1% resistors should be used (See
). Decouple VREF
locally at the divider and DIMMs/MCH using one 0.1uF capacitor per VREF pin.
Figure 6-16. DDR VREF Voltage Regulator
DDR VDD
(2.5V)
Voltage
Regulator
DDR VTT
(1.25V)
Vin
Vout
DDR VREF
(1.25V)
Ref
0.1
µ
F
Figure 6-17. DDR VREF Voltage Divider
Voltage
Regulator
DDR VTT
(1.25V)
Vin
Vout
DDR VREF
(1.25V)
DDR VDD
(2.5V)
1%
1%
0.1
µ
F
Summary of Contents for Xeon
Page 24: ...Introduction 24 Design Guide This page is intentionally left blank ...
Page 30: ...Component Quadrant Layout 30 Design Guide This page is intentionally left blank ...
Page 52: ...Platform Clock Routing Guidelines 52 Design Guide This page is intentionally left blank ...
Page 66: ...System Bus Routing Guidelines 66 Design Guide This page is intentionally left blank ...
Page 118: ...Intel 82870P2 P64H2 118 Design Guide This page is intentionally left blank ...
Page 146: ...I O Controller Hub 146 Design Guide This page is intentionally left blank ...
Page 148: ...Debug Port 148 Design Guide This page is intentionally left blank ...
Page 210: ...Schematic Checklist 210 Design Guide This page is intentionally left blank ...
Page 220: ...Layout Checklist 220 Design Guide This page is intentionally left blank ...
Page 222: ...Schematics 222 Design Guide This page is intentionally left blank ...