G2995 Datasheet, PDF (10/12 Pages) Global Mixed-mode Technology Inc – DDR Termination Regulator

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.
V_DDQ=1.8V
V_DDQ
V_REF
AV_IN=1.8V or 5.5V
PV_IN=1.8V
C_IN ⁺
AV_IN
PV_IN
V_SENSE
V_TT
GND
+
V_REF=0.9V
C_REF
V_TT=0.9V
+
C_OUT
Figure 5. Recommended DDR-II Termination
V_DDQ=1.8V
V_DDQ
V_REF
AV_IN=3.3V or 5.5V
PV_IN=3.3V
C_IN ⁺
AV_IN
PV_IN
V_SENSE
V_TT
GND
+
V_REF=0.9V
C_REF
V_TT=0.9V
+
C_OUT
Figure 6. DDR-II Termination with higher voltage rails
Figure 7 & 8 are used to scale the V_TT to the wanted
value when the standard voltages of SSTL-2 do not
meet the requirements. Using R1 & R2, Figure 7 can
shift V_TT up to VDDQ/2 * (1+R1/R2) and figure 8 can
shift V_TT down to VDDQ/2 * (1-R1/R2).
V_DDQ
V_DD
C_IN ⁺
V_DDQ
AV_IN
V_TT
PV_IN
V_SENSE
GND
V_TT
R1
+
C_OUT
R2
Figure 7. Increasing VTT by Level Shifting
V_DDQ
V_DD
R2
V_DDQ
V_SENSE
R1
AV_IN
C_IN ⁺
PV_IN
V_TT
GND
V_TT
+
C_OUT
Figure 8. Decreasing VTT by Level Shifting
Ver: 1.7
May 10, 2005
TEL: [phone]
http://www.gmt.com.tw
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