LP2998EVAL National Semiconductor, LP2998EVAL Datasheet - Page 11

• Manufacturer Part Number: LP2998EVAL
• Description: BOARD EVALUATION FOR LP2998
• Manufacturer: National Semiconductor

Specifications of LP2998EVAL

• Channels Per Ic: 1 - Single
• Current - Output: 1.5A
• Voltage - Input: 2.2 ~ 5.5V
• Regulator Type: Positive Fixed
• Operating Temperature: -40°C ~ 125°C
• Board Type: Fully Populated
• Utilized Ic / Part: LP2998
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Voltage - Output: -

standard.
the two boards mentioned.
Additional improvements can be made by the judicious use of
vias to connect the part and dissipate heat to an internal
ground plane. Using larger traces and more copper on the top
side of the board can also help. With careful layout, it is pos-
sible to reduce the θ
in
Optimizing the θ
board exposed to lower ambient temperature allows the part
Figure 2
Figure 2
FIGURE 2. θ
JA
shows how the θ
and placing the LP2998 in a section of a
JA
further than the nominal values shown
JA
vs Airflow (SO-8)
JA
varies with airflow for
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11
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
ing, and quiescent currents at AVIN and VDDQ. During the
active state (when shutdown is not held low) the total internal
power dissipation can be calculated from the following equa-
tions:
Where,
To calculate the maximum power dissipation at V
sinking and sourcing current conditions need to be examined.
Although only one equation will add into the total, V
source and sink current simultaneously.
The power dissipation of the LP2998 can also be calculated
during the shutdown state. During this condition the output
V
will disappear as it cannot sink or source any current (leakage
is negligible). The only losses during shutdown will be the re-
duced quiescent current at AVIN and the constant impedance
that is seen at the VDDQ pin.
TT
will tri-state. Therefore, that term in the power equation
P
P
P
VDDQ
VDDQ
VTT
P
= ( V
VTT
= V
= V
P
D
= V
VDDQ
VDDQ
= P
P
P
PVIN
P
AVIN
AVIN
D
VTT
AVIN
= P
- V
* I
* I
= I
= I
x I
AVIN
VDDQ
VDDQ
VTT
+ P
AVIN
AVIN
LOAD
) x I
VDDQ
+ P
= V
= V
* V
x V
(Sinking) or
TT
LOAD
VDDQ
AVIN
AVIN
, either sinking or sourc-
VDDQ
VDDQ
+ P
(Sourcing)
VTT
2
2
x R
x R
VDDQ
VDDQ
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TT
, both the
TT
cannot