TPS51200
www.ti.com
SLUS812–FEBRUARY 2008
Output Tolerance Consideration for VTT DIMM Applications
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.
DDR3 240 Pin Socket
VO
TPS51200
10 mF
10 mF
10 mF
UDG-08022
Figure 3. Typical Application Diagram for DDR3 VTT DIMM using TPS51200
V
V
TT
DDQ
Q1
Q2
25 W
R
S
20 W
Receiver
Ouput
Buffer
(Driver)
V
V
IN
OUT
V
SS
UDG-08023
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
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