Datasheet

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Output Tolerance Consideration for VTT DIMM Applications
DDR3 240 Pin Socket
TPS51200
10 mF 10 mF 10 mF
VO
SPD
Vtt
DQ
Vdd
Vtt
Vdd
CA CA
Vdd
DQ
UDG-08022
R
S
20 W
V
OUT
V
IN
25 W
V
TT
V
DDQ
Ouput
Buffer
(Driver)
Receiver
V
SS
UDG-08023
Q1
Q2
TPS51200
SLUS812 – FEBRUARY 2008
The TPS51200 is specifically designed to power up the memory termination rail (as shown in Figure 3 ). The DDR
memory termination structure determines the main characteristics of the VTT rail, which is to be able to sink and
source current while maintaining acceptable VTT tolerance. See Figure 4 for typical characteristics for a single
memory cell.
Figure 3. Typical Application Diagram for DDR3 VTT DIMM using TPS51200
Figure 4. DDR Physical Signal System Bi-Directional SSTL Signaling
In Figure 4 , when Q1 is on and Q2 is off:
• Current flows from VDDQ via the termination resistor to VTT
• VTT sinks current
In Figure 4 , when Q2 is on and Q1 is off:
• Current flows from VTT via the termination resistor to GND
• VTT sources current
Copyright © 2008, Texas Instruments Incorporated 11
Product Folder Link(s): TPS51200