Datasheet
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AV02-4078EN - May 10, 2013
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Thermal Model for ACPL-P346/W346 Stretched SO6 Package Optocoupler
This thermal model assumes that an 6-pin single-channel
plastic package optocoupler is soldered into a 7.62 cm x
7.62 cm printed circuit board (PCB) per JEDEC standards.
The temperature at the LED and Detector junctions of the
optocoupler can be calculated using the equations below.
T
1
= (R
11
* P
1
+ R
12
* P
2
) + Ta -- (1)
T
2
= (R
21
* P
1
+ R
22
* P
2
) + Ta -- (2)
Using the given thermal resistances and thermal model
formula in this datasheet, we can calculate the junction
temperature for both LED and the output detector. Both
junction temperatures should be within the absolute
maximum rating.
For example, given P
1
= 17 mW, P
2
= 124 mW, Ta = 85 °C:
LED junction temperature,
T
1
= (R
11
* P
1
+ R
12
* P
2
) + Ta
= (135 * 0.017 + 27 * 0.124) + 85
= 90.7 °C
Output IC junction temperature,
T
2
= (R
21
x P
1
+ R
22
x P
2
) + Ta
= (39 *0.017 + 47 * 0.124) + 85
= 91.5 °C
T
1
and T
2
should be limited to 125 °C based on the board
layout and part placement.
Denitions:
R
11
: Junction to Ambient Thermal Resistance of LED due
to heating of LED
R
12
: Junction to Ambient Thermal Resistance of LED due
to heating of Detector (Output IC)
R
21
: Junction to Ambient Thermal Resistance of Detector
(Output IC) due to heating of LED.
R
22
: Junction to Ambient Thermal Resistance of Detector
(Output IC) due to heating of Detector (Output IC).
P
1
: Power dissipation of LED (W).
P
2
: Power dissipation of Detector / Output IC (W).
T
1
: Junction temperature of LED (˚C).
T
2
: Junction temperature of Detector (˚C).
Ta: Ambient temperature.
Ambient Temperature: Junction to Ambient Thermal Re-
sistances were measured approximately 1.25 cm above
optocoupler at ~23 ˚C in still air
Thermal Resistance °C/W
R
11
135
R
12
27
R
21
39
R
22
47