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FOD2741A, FOD2741B, FOD2741C — Optically Isolated Error Amplifier
August 2008
FOD2741A, FOD2741B, FOD2741C
Optically Isolated Error Amplifier
Features
■
Optocoupler, precision reference and error amplifier in
■
■
■
■
Description
The FOD2741 Optically Isolated Amplifier consists of the
popular KA431 precision programmable shunt reference
and an optocoupler. The optocoupler is a gallium ars-
enide (GaAs) light emitting diode optically coupled to a
silicon phototransistor. It comes in 3 grades of reference
voltage tolerance = 2%, 1%, and 0.5%.
The Current Transfer Ratio (CTR) ranges from 100% to
200%. It also has an outstanding temperature coefficient
of 50 ppm/°C. It is primarily intended for use as the error
amplifier/reference voltage/optocoupler function in iso-
lated AC to DC power supplies and DC/DC converters.
When using the FOD2741, power supply designers can
reduce the component count and save space in tightly
packaged designs. The tight tolerance reference elimi-
nates the need for adjustments in many applications.
The device comes in a 8-pin dip white package.
■
■
single package
2.5V reference
CTR 100% to 200%
5,000V RMS isolation
UL approved E90700, Volume 2
CSA approval 1296837
VDE approval 40002463
BSI approval 8702, 8703
Low temperature coefficient 50ppm/°C max.
FOD2741A: tolerance 0.5%
FOD2741B: tolerance 1%
FOD2741C: tolerance 2%
Applications
■
Power supplies regulation
■
DC to DC converters
Functional Bock Diagram
Package Outlines
NC
1
8 LED
8
1
C
2
7 FB
E
3
6 COMP
8
8
1
1
NC
4
5 GND
©2004 Fairchild Semiconductor Corporation
FOD2741A, FOD2741B, FOD2741C Rev. 1.0.1
www.fairchildsemi.com
FOD2741A, FOD2741B, FOD2741C — Optically Isolated Error Amplifier
Pin Definitions
Pin Number
1
2
3
4
5
6
7
8
Pin Name
NC
C
E
NC
GND
COMP
FB
LED
Not connected
Phototransistor Collector
Phototransistor Emitter
Not connected
Ground
Pin Description
Error Amplifier Compensation. This pin is the output of the error amplifier.*
Voltage Feedback. This pin is the inverting input to the error amplifier
Anode LED. This pin is the input to the light emitting diode.
*The compensation network must be attached between pins 6 and 7.
Typical Application
V
1
FAN4803
PWM
Control
V
O
FOD2741
2
8
6
R1
3
7
R2
5
©2004 Fairchild Semiconductor Corporation
FOD2741A, FOD2741B, FOD2741C Rev. 1.0.1
www.fairchildsemi.com
2
FOD2741A, FOD2741B, FOD2741C — Optically Isolated Error Amplifier
Absolute Maximum Ratings
(T
A
= 25°C unless otherwise specified)
Stresses exceeding the absolute maximum ratings may damage the device. The device may not function or be
operable above the recommended operating conditions and stressing the parts to these levels is not recommended.
In addition, extended exposure to stresses above the recommended operating conditions may affect device reliability.
The absolute maximum ratings are stress ratings only.
Symbol
T
STG
T
OPR
T
SOL
V
LED
I
LED
V
CEO
V
ECO
I
C
PD1
PD2
PD3
Parameter
Storage Temperature
Operating Temperature
Lead Solder Temperature
Input Voltage
Input DC Current
Collector-Emitter Voltage
Emitter-Collector Voltage
Collector Current
Input Power Dissipation
(1)
Transistor Power Dissipation
(2)
Total Power Dissipation
(3)
Value
-40 to +125
-40 to +85
260 for 10 sec.
37
20
30
7
50
145
85
145
Units
°C
°C
°C
V
mA
V
V
mA
mW
mW
mW
Notes:
1. Derate linearly from 25°C at a rate of 2.42mW/°C
2. Derate linearly from 25°C at a rate of 1.42mW/°C.
3. Derate linearly from 25°C at a rate of 2.42mW/°C.
©2004 Fairchild Semiconductor Corporation
FOD2741A, FOD2741B, FOD2741C Rev. 1.0.1
www.fairchildsemi.com
3
FOD2741A, FOD2741B, FOD2741C — Optically Isolated Error Amplifier
Electrical Characteristics
(T
A
= 25°C unless otherwise specified)
Input Characteristics
Symbol
V
F
V
REF
Parameter
LED Forward Voltage
Reference Voltage
Test Conditions
I
LED
= 10mA, V
COMP
= V
FB
(Fig.1)
I
LED
= 10mA, V
COMP
= V
FB
Device
All
FOD2741A
FOD2741B
Min.
2.482
2.470
Typ. Max. Unit
1.5
2.495
2.495
2.500
4.5
-1.0
-0.5
2.508
2.520
2.550
17
-2.7
-2.0
4
1.2
1.0
1.0
0.5
µA
µA
mA
µA
Ω
V
V
V
V
mV
mV/V
FOD2741C 2.450
V
REF (DEV)(4)
Deviation of V
REF
Over T
A
= -25°C to +85°C
Temperature
∆
V
REF
/
∆
V
COMP
I
REF
Ratio of V
REF
Variation I
LED
= 10mA
∆
V
COMP
= 10V to V
REF
to the Output of the
∆
V
COMP
= 36V to 10V
Error Amplifier
Feedback Input
Current
I
LED
= 10mA, R
1
= 10k
Ω
(Fig. 3)
T
A
= -25°C to +85°C
All
All
All
All
All
All
All
1.5
0.4
0.45
0.05
0.15
I
REF (DEV)(4)
Deviation of I
REF
Over
Temperature
I
LED (MIN)
I
(OFF)
|Z
OUT
|
Minimum Drive Current V
COMP
= V
FB
(Fig. 1)
Off-state Error
V
LED
= 37V, V
FB
= 0 (Fig. 4)
Amplifier Current
Error Amplifier Output
impedance
(5)
V
COMP
= V
REF
, I
LED
= 1mA to 20mA,
f
≥
1.0 kHz
Output Characteristics
Symbol
I
CEO
BV
ECO
BV
CEO
Parameter
Collector Dark Current
Emitter-Collector Voltage Breakdown
Collector-Emitter Voltage Breakdown
Test Conditions
V
CE
= 10V (Fig. 5)
I
E
= 100µA
I
C
= 1.0mA
Min.
7
70
Typ.
Max.
50
Unit
nA
V
V
Transfer Characteristics
Symbol
Parameter
CTR
Current Transfer Ratio
Test Conditions
I
LED
= 10mA, V
COMP
= V
FB
,
V
CE
= 5V (Fig. 6)
I
LED
= 10mA, V
COMP
= V
FB,
I
C
= 2.5mA (Fig. 6)
Min.
100
Typ.
Max.
200
0.4
Unit
%
V
V
CE (SAT)
Collector-Emitter Saturation
Voltage
Notes:
4. The deviation parameters V
REF(DEV)
and I
REF(DEV)
are defined as the differences between the maximum and
minimum values obtained over the rated temperature range. The average full-range temperature coefficient of the
reference input voltage,
∆
V
REF
, is defined as:
∆V
REF
{
V
REF
(
DEV
)
/V
REF
(
T
A
= 25°C
) } ×
10
(
ppm/°C
)
= ----------------------------------------------------------------------------------------------------
-
∆T
A
6
where
∆
T
A
is the rated operating free-air temperature range of the device.
5. The dynamic impedance is defined as |Z
OUT
| =
∆
V
COMP
/
∆
I
LED
. When the device is operating with two external
resistors (see Figure 2), the total dynamic impedance of the circuit is given by:
∆V
R1
Z
OUT, TOT
= -------
≈
Z
OUT
×
1 + -------
-
-
∆I
R2
©2004 Fairchild Semiconductor Corporation
FOD2741A, FOD2741B, FOD2741C Rev. 1.0.1
www.fairchildsemi.com
4
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