Global Mixed-mode Technology Inc.
G2995
In Figure 5 & 6, they are the application configurations
of DDR-II SDRAM bus terminations. Figure 5 is the
typical application scheme of DDR-II SDRAM. With the
separate VDDQ pin and an internal resistor divider, it
is possible to use the G2995 in applications utilizing
DDR-II memory. Figure 6 is used to increase the driv-
ing capability. The risk is the same as figure 4.
VREF
VREF=0.9V
VDDQ
VDDQ=1.8V
+
+
CREF
VSENSE
VTT
AVIN=1.8V or 5.5V
PVIN=1.8V
AVIN
PVIN
VTT=0.9V
COUT
+
GND
CIN
Figure 5. Recommended DDR-II Termination
VREF
VREF=0.9V
CREF
VDDQ
VDDQ=1.8V
+
VSENSE
VTT
AVIN=3.3V or 5.5V
PVIN=3.3V
AVIN
PVIN
VTT=0.9V
COUT
+
+
GND
CIN
Figure 6. DDR-II Termination with higher voltage rails
Figure 7 & 8 are used to scale the VTT to the wanted
value when the standard voltages of SSTL-2 do not
meet the requirements. Using R1 & R2, Figure 7 can
shift VTT up to VDDQ/2 * (1+R1/R2) and figure 8 can
shift VTT down to VDDQ/2 * (1-R1/R2).
VDDQ
VDD
VDDQ
AVIN
PVIN
VTT
VTT
COUT
R1
R2
+
VSENSE
+
GND
CIN
Figure 7. Increasing VTT by Level Shifting
R2
VDDQ
VDD
VDDQ
AVIN
PVIN
VSENSE
R1
VTT
COUT
VTT
+
+
GND
CIN
Figure 8. Decreasing VTT by Level Shifting
TEL: 886-3-5788833
http://www.gmt.com.tw
Ver: 1.6
Jul 26, 2004
10
GMT [ GLOBAL MIXED-MODE TECHNOLOGY INC ]
