Datasheet

LT1210
13
1210fb
For more information www.linear.com/LT1210
applicaTions inForMaTion
T7 Package, 7-Lead TO-220
Thermal Resistance (Junction-to-Case) = 5°C/W
Calculating Junction Temperature
The junction temperature can be calculated from the
equation:
T
J
= (P
D
)(θ
JA
) + T
A
where:
T
J
= Junction Temperature
T
A
= Ambient Temperature
P
D
= Device Dissipation
θ
JA
= Thermal Resistance (Junction-to-Ambient)
As an example, calculate the junction temperature for the
circuit in Figure 7 for the SO and R packages assuming a
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 and feedback
network.
P
D
= (76mA)(10V) – (1.4V)
2
/ 10 = 0.56W
Figure 7
then:
T
J
= (0.56W)(46°C/W) + 70°C = 96°C
for the SO package with 1000 sq. mm topside
heat sinking
T
J
= (0.56W)(27°C/W) + 70°C = 85°C
for the R package with 1000 sq. mm topside heat
sinking
Since the maximum junction temperature is 150°C,
both packages are clearly acceptable.
–
+
LT1210
SD
5V
–5V
680Ω
220Ω
10Ω
0V
2V
V
O
V
O
= 1.4V
RMS
76mA
1210 F07
–2V
A
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