lt1969cms-trpbf Linear Technology Corporation, lt1969cms-trpbf Datasheet - Page 11

• Manufacturer Part Number: lt1969cms-trpbf
• Description: Dual 700mhz, 200ma, Adjustable Current Operational Amplifier
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
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
*Device is mounted on topside.
Calculating Junction Temperature
The junction temperature can be calculated from the
equation:
TOPSIDE*
T
T
T
P
(mm
J
J
A
JA
540
100
100
D
30
COPPER AREA
0
= (P
= Junction Temperature
= Ambient Temperature
= Device Dissipation
2
= Thermal Resistance (Junction-to-Ambient)
)
D
)(
BACKSIDE
(mm
JA
540
100
0
0
0
) + T
2
)
U
A
BOARD AREA
U
(mm
2500
2500
2500
2500
2500
2
CTRL1
)
–6V
6
13k
W
(JUNCTION-TO-AMBIENT)
THERMAL RESISTANCE
CTRL2
–6V
7
49.9k
Figure 1. Thermal Calculation Example
110 C/W
120 C/W
130 C/W
135 C/W
140 C/W
100
U
100
+
–
–
+
–6V
6V
As an example, calculate the junction temperature for the
circuit in Figure 1 assuming an 70 C ambient temperature.
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:
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 T
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:
which is above the maximum junction temperature indi-
cating that the heat sinking capability of the board is
inadequate and should be increased.
909
1K
P
T
T
J
J
D
= (0.6W)(110 C/W) + 70 C = 136 C
= (0.6W)(140 C/W) + 70 C = 154 C
= (63.5mA)(12V) – (4V/ 2)
50
f = 1MHz
1969 F01
4V
–4V
J
is:
2
/(50) = 0.6W
LT1969
11