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LT1969 Fiches technique(PDF) 11 Page - Linear Technology

No de pièce LT1969
Description  Dual 700MHz, 200mA, Adjustable Current Operational Amplifier
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Fabricant  LINER [Linear Technology]
Site Internet  http://www.linear.com
Logo LINER - Linear Technology

LT1969 Fiches technique(HTML) 11 Page - Linear Technology

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11
LT1969
were taken in still air on 3/32" FR-4 board with 2oz copper.
This data can be used as a rough guideline in estimating
thermal resistance. The thermal resistance for each appli-
cation will be affected by thermal interactions with other
components as well as board size and shape.
Table 1. Fused 10-Lead MSOP Package
COPPER AREA
TOPSIDE*
BACKSIDE
BOARD AREA
THERMAL RESISTANCE
(mm2)(mm2)(mm2)
(JUNCTION-TO-AMBIENT)
540
540
2500
110
°C/W
100
100
2500
120
°C/W
100
0
2500
130
°C/W
30
0
2500
135
°C/W
0
0
2500
140
°C/W
*Device is mounted on topside.
Calculating Junction Temperature
The junction temperature can be calculated from the
equation:
TJ = (PD)(θJA) + TA
TJ = Junction Temperature
TA = Ambient Temperature
PD = Device Dissipation
θJA = Thermal Resistance (Junction-to-Ambient)
As an example, calculate the junction temperature for the
circuit in Figure 1 assuming an 70
°Cambienttemperature.
The device dissipation can be found by measuring the
supply currents, calculating the total dissipation and then
subtracting the dissipation in the load.
The dissipation for the amplifiers is:
PD = (63.5mA)(12V) – (4V/√2)2/(50) = 0.6W
The total package power dissipation is 0.6W. When a 2500
sq. mm PC board with 540 sq. mm of 2oz copper on top
and bottom is used, the thermal resistance is 110
°C/W.
The junction temperature TJ is:
TJ = (0.6W)(110°C/W) + 70°C = 136°C
The maximum junction temperature for the LT1969 is
150
°C so the heat sinking capability of the board is
adequate for the application.
If the copper area on the PC board is reduced to 0 sq. mm
the thermal resistance increases to 140
°C/W and the
junction temperature becomes:
TJ = (0.6W)(140°C/W) + 70°C = 154°C
which is above the maximum junction temperature indi-
cating that the heat sinking capability of the board is
inadequate and should be increased.
APPLICATIO S I FOR ATIO
Figure 1. Thermal Calculation Example
+
6V
–6V
–6V
–6V
909
100
100
1969 F01
1K
50
–4V
4V
f = 1MHz
13k
6
49.9k
CTRL1
CTRL2
7


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