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參數(shù)資料
| 型號： | LM8207MTX |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 模擬信號調(diào)理 |
| 英文描述： | TFT 18 Gamma Buffer + VCOM Driver + Voltage Reference |
| 中文描述： | SPECIALTY ANALOG CIRCUIT, PDSO48 |
| 封裝： | TSSOP-48 |
| 文件頁數(shù)： | 19/22頁 |
| 文件大小： | 1393K |
| 代理商： | LM8207MTX |
Application Section
(Continued)
MAXIMUM POWER DISSIPATION
The maximum power dissipation in the LM8207 TSSOP
package depends on the ambient temperature and the in-
crease of the junction temperature of the die. Exceeding the
maximum temperature will damage the part. (See the Abso-
lute Maximum Ratings table on page 2 of the datasheet.)
The V
buffer of the LM8207 is designed for use in pulsed
conditions. Driving a continuous current of several hundred
mA to a load will damage the part due to the high power
consumption of the output stage of the V
COM
buffer.
The maximum operating temperature can be calculated us-
ing this formula:
T
J
= T
A
+
θ
JA
x P
DISSIPATION
Where
(3)
T
A
θ
JA
= Ambient temperature
= Thermal resistance of package (See
Operating Ratings table on page 2)
(84C/W)
P
DISSIPATION
= Total power dissipation of the LM8207
Example:
The estimated power consumption of the LM8207 in a
steady state situation with no load is:
V
DD
I
DD
= 16V
= 6 mA (all buffers within
normal operating range)
= 14.4V
= 3 mA
= 16 V x 6 mA
OUT_V
REF
I
LOAD
V
DD
x I
DD
(V
DD
- OUT_V
REF
) x I
LOAD
=
(16 V – 14.4 V) x 3 mA
Total steady state power
dissipation
= 4.8 mW
= 100.8 mW
For an ambient temperature T
of 40C and a dissipated
power of 100.8 mW, the junction temperature T
will be 49C.
This will not exceed the maximum operating temperature.
Two issues are not considered in the calculation:
Continuous power dissipation of the gamma buffers. This
is load dependent, and can be calculated using the volt-
age drop over the output stage times the output current:
P = (V
DD
-V
GMAx
) x I
OUT
for current sourcing
P = (V
GMAx
) x I
OUT
for current sinking
Pulsed power dissipation of the buffers. The RMS value
of this pulsed current depends on the magnitude of the
current fluctuations and the duty cycle. This can majorly
contribute to the total power dissipation.
Example:
When the LM8207 is in steady state biasing, the V buffer is
considered at three various load conditions:
I
OUTRMS
(mA)
10
50
100
When I
= 100 mA, the package (T
J
) will exceed the Operating
Temperature!
V
COM
Level (V)
8
8
8
Dissipation
(mW)
80
400
800
Temp
Rise
7
35
67
T
J
56
83
107
EVALUATION BOARD
For testing purposes an evaluation board is available. It is
intended to evaluate the following functions:
The Voltage Reference is fully adjustable within the op-
erating range. For optimal output voltage ranges, user
defined resistors can be trimmed by using two resistors in
series.
The Gamma correction curve is user defined using exter-
nal resistors. Each optimal value can be achieved by
using two series resistors for fine-tuning.
The V
node input voltage can be achieved using
National Semiconductor’s LM8342 programmable V
COM
calibrator, or using an external supply.
For testing, an additional dummy load can be connected
to all outputs of the gamma buffers.
L
www.national.com
19
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