LP2997MX National Semiconductor, LP2997MX Datasheet - Page 9

• Manufacturer Part Number: LP2997MX
• Description: DDR-II Termination Regulator
• Manufacturer: National Semiconductor

Thermal Dissipation
top side of the board can also help. With careful layout it is
possible to reduce the θ
shown in Figure 1
Optimizing the θ
board exposed to lower ambient temperature allows the part
to operate with higher power dissipation. The internal power
dissipation can be calculated by summing the three main
sources of loss: output current at V
sourcing, and quiescent current at AVIN and VDDQ. During
the active state (when shutdown is not held low) the total
internal power dissipation can be calculated from the follow-
ing equations:
Where,
P
VDDQ
= V
P
JA
D
VDDQ
and placing the LP2997 in a section of a
= P
P
AVIN
AVIN
JA
* I
= I
VDDQ
+ P
further than the nominal values
AVIN
VDDQ
= V
* V
(Continued)
AVIN
VDDQ 2
+ P
TT
, either sinking or
VTT
x R
VDDQ
9
To calculate the maximum power dissipation at V
conditions at V
current. Although only one equation will add into the total,
V
The power dissipation of the LP2997 can also be calculated
during the shutdown state. During this condition the output
V
will disappear as it cannot sink or source any current (leak-
age 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.
TT
TT
cannot source and sink current simultaneously.
will tri-state, therefore that term in the power equation
P
P
VDDQ
VTT
P
TT
= ( V
VTT
= V
need to be examined, sinking and sourcing
= V
VDDQ
P
PVIN
P
AVIN
D
VTT
= P
- V
* I
= I
x I
AVIN
VDDQ
VTT
AVIN
LOAD
) x I
+ P
x V
= V
(Sinking) or
LOAD
VDDQ
AVIN
VDDQ 2
(Sourcing)
x R
VDDQ
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TT
both