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Data subject to change. Copyright © 2005-2011 Avago Technologies. All rights reserved.
AV02-2928EN - November 14, 2011
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 di erential mode noise
immunity and minimizes the potential for output signal
chatter.
Under Voltage Lockout
The ACPL-P343/W343 Under Voltage Lockout (UVLO)
feature is designed to prevent the application of insu -
cient gate voltage to the IGBT by forcing the ACPL-P343/
W343 output low during power-up. IGBTs typically require
gate voltages of 15 V to achieve their rated V
CE(ON)
voltage.
At gate voltages below 13 V typically, the V
CE(ON)
voltage
increases dramatically, especially at higher currents. At
very low gate voltages (below 10 V), the IGBT may operate
in the linear region and quickly overheat. The UVLO
function causes the output to be clamped whenever
insu cient operating supply (V
CC
) is applied. Once V
CC
exceeds V
UVLO+
(the positive-going UVLO threshold), the
UVLO clamp is released to allow the device output to turn
on in response to input signals.
Thermal Model for ACPL-P343/W343 Stretched SO6
Package Optocoupler
De nitions:
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
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 temperature should be within the absolute
maximum rating.
For example, given P
1
= 25 mW, P
2
= 185 mW, Ta = 85° C:
LED junction temperature,
T
1
= (R
11
* P
1
+ R
12
* P
2
) + Ta
= (135 * 0.025 + 27 * 0.185) + 85
= 93.4° C
Output IC junction temperature,
T
2
= (R
21
* P
1
+ R
22
* P
2
) + Ta
= (39 *0.025 + 47 * 0.185) + 85
= 94.7° C
T
1
and T
2
should be limited to 125° C based on the board
layout and part placement.
Related Application Noted
AN5336 – Gate Drive Optocoupler Basic Design for IGBT/
MOSFET
AN1043 – Common-Mode Noise: Sources and Solutions
AV02-0310EN – Plastics Optocouplers Product ESD and
Moisture Sensitivity
