Broadcom Condential
- 13 -
ACPL-P347/ACPL-W347 Data Sheet
LED Current Input with Hysteresis
The detector has optical receiver input stage with built in
Schmitt trigger to provide logic compatible waveforms,
eliminating the need for additional wave shaping. The
hysteresis (Figure 12) provides dierential mode noise
immunity and minimizes the potential for output signal
chatter.
Thermal Model for ACPL-P347/W347
Stretched SO6 Package Optocoupler
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).
T
A
: Ambient temperature.
Ambient Temperature: Junction to Ambient Thermal
Resistances 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
This thermal model assumes that an 6-pin single-channel
plastic package optocoupler is soldered into a 7.62 cm ×
7.62 cm printed circuit board (PCB) per JEDEC standards. The
temperature at the LED and Detector junctions of the opto-
coupler 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.
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