LP2996A Datasheet, PDF (13/29 Pages) Texas Instruments – DDR Termination Regulator

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LP2996A
SNOSCY7 – JUNE 2014
Application Information (continued)
P_VTT = ( V_PVIN - V_VTT) x I_LOAD (Sourcing
(7)
The power dissipation of the LP2996A can also be calculated during the shutdown state. During this condition
the output V_TT will tri-state, therefore that term in the power equation will disappear as it cannot sink or source
any current (leakage is negligible). The only losses during shutdown will be the reduced quiescent current at
AVIN and the constant impedance that is seen at the VDDQ pin.
P_D = P_AVIN + P_VDDQ
P_AVIN = I_AVIN x V_AVIN
P_VDDQ = V_VDDQ * I_VDDQ = V_VDDQ2 x R_VDDQ
(8)
(9)
(10)
8.2 Typical Application
Several different application circuits are shown below to illustrate some of the options that are possible in
configuring the LP2996A. Graphs of the individual circuit performance can be found in the Typical Performance
Characteristics section in the beginning of the datasheet. These curves illustrate how the maximum output
current is affected by changes in AVIN and PVIN.
8.2.1 Typical Application Circuit
SD
VDDQ = 1.5V
VDD = 2.5V
+
472F
LP2996A
SD
VDDQ
VREF
AVIN
VSENSE
PVIN
VTT
GND
VREF = 0.75V
+
0.012F
VTT = 0.75V
+
2202F
Figure 19. Typical Application Circuit
8.2.2 DDR-III Applications
With the separate VDDQ pin and an internal resistor divider it is possible to use the LP2996A in applications
utilizing DDR-III memory. The output stage is connected to the 1.5 V rail and the AVIN pin can be connected to a
2.2 V - 5.5 V rail.
LP2996A
SD
VDDQ = 1.5V
AVIN = 2.2V to 5.5V
PVIN = 1.5V
+
CIN
SD
VDDQ
VREF
AVIN
VSENSE
PVIN
VTT
GND
+
CREF
VREF = 0.75V
+
COUT
VTT = 0.75V
Figure 20. Recommended DDR-III Termination
If it is not desirable to use the 1.5 V - 2.5 V rail it is possible to connect the output stage to a 3.3 V rail. Care
should be taken to not exceed the maximum junction temperature as the thermal dissipation increases with lower
V_TT output voltages. For this reason it is not recommended to power PVIN off a rail higher than the nominal 3.3
V. The advantage of this configuration is that it has the ability to source and sink a higher maximum continuous
current.
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