OPTICALLY ISOLATED
ERROR AMPLIFIER
FOD2741A
DESCRIPTION
The FOD2741 Optically Isolated Amplifier consists of the popular KA431 precision
programmable shunt reference and an optocoupler. The optocoupler is a gallium arsenide
(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 isolated ac to dc power supplies and dc/dc con-
verters.
When using the FOD2741, power supply designers can reduce the component count and
save space in tightly packaged designs. The tight tolerance reference eliminates the need
for adjustments in many applications. The device comes in a 8-pin dip white package.
8
1
8
1
8
1
FOD2741B
FOD2741C
FEATURES
•
•
•
•
•
Optocoupler, precision reference and error amplifier in 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 50 ppm/°C max
• FOD2741A: tolerance 0.5%
FOD2741B: tolerance 1%
FOD2741C: tolerance 2%
FUNCTIONAL BLOCK DIAGRAM
NC
1
8 LED
C
2
7 FB
E
3
6 COMP
NC
4
5 GND
APPLICATIONS
• Power supplies regulation
• DC to DC converters
PIN DEFINITIONS
Pin Number
1
2
3
4
5
6
7
8
Pin Name
NC
C
E
NC
GND
COMP
FB
LED
Pin function description
Not connected
Phototransistor Collector
Phototransistor Emitter
Not connected
Ground
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.
© 2002 Fairchild Semiconductor Corporation
Page 1 of 14
10/29/02
OPTICALLY ISOLATED
ERROR AMPLIFIER
FOD2741A
TYPICAL APPLICATION
FOD2741B
FOD2741C
V
1
FAN4803
PWM
Control
V
O
FOD2741
2
8
6
R1
3
7
R2
5
ABSOLUTE MAXIMUM RATINGS
(T
A
= 25°C Unless otherwise specified.)
Parameter
Storage Temperature
Operating Temperature
Lead Solder Temperature
Input Voltage
Input DC Current
Collector-Emitter Voltage
Emitter-Collector Voltage
Collector Current
Input Power Dissipation (note 1)
Transistor Power Dissipation (note 2)
Total Power Dissipation (note 3)
Symbol
T
STG
T
OPR
T
SOL
V
LED
I
LED
V
CEO
V
ECO
I
C
PD1
PD2
PD3
Value
-55 to +125
-25 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 2.42 mW/ °C
2. Derate linearly from 25°C at a rate of 1.42 mW/ °C.
3. Derate linearly from 25°C at a rate of 2.42 mW/ °C.
4. Functional operation under these conditions is not implied. Permanent damage may occur if the device is subjected to conditions
outside these ratings.
© 2002 Fairchild Semiconductor Corporation
Page 2 of 14
10/29/02
OPTICALLY ISOLATED
ERROR AMPLIFIER
FOD2741A
FOD2741B
FOD2741C
ELECTRICAL CHARACTERISTICS
(T
A
= 25°C Unless otherwise specified.)
INPUT CHARACTERISTICS
Parameter
LED Forward Voltage
Test Conditions
(I
LED
= 10 mA, V
COMP
= V
FB
) (fig.1)
I
LED
= 10 mA, V
COMP
= V
FB
Symbol
V
F
V
REF
Device
ALL
A
Reference Voltage
Deviation of V
REF
over
temperature
Ratio of V
REF
variation to the
output of the error amplifier
Feedback Input Current
Deviation of I
REF
over
temperature
Minimum Drive Current
Off-state error amplifier current
Error amplifier output impedance
(see note 2)
I
LED
= 10 mA
B
C
T
A
= -25°C to +85°C V
REF (DEV)
∆
V
COMP
= 10V to V
REF
∆
V
COMP
= 36V to 10V
∆
V
REF
/
∆
V
COMP
I
REF
I
REF (DEV)
I
LED (MIN)
I
(OFF)
|Z
OUT
|
ALL
ALL
ALL
ALL
ALL
ALL
ALL
2.482
2.470
2.450
2.495
2.495
2.500
4.5
-1.0
-0.5
1.5
0.4
0.45
0.05
0.15
Min.
Typ.
Max.
1.5
2.508
2.520
2.550
17
-2.7
-2.0
4
1.2
1.0
1.0
0.5
Unit
V
V
V
V
mV
mV/
V
µA
µA
mA
µA
Ω
I
LED
= 10mA, R
1
= 10k
Ω
(fig 3)
T
A
= -25°C to +85°C
V
COMP
= V
FB
(fig.1)
V
LED
= 37V, V
FB
= 0 (fig 4.)
V
COMP
= V
REF
, I
LED
= 1mA to 20mA,
f
≥
1.0 kHz
1. 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.
2. 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
© 2002 Fairchild Semiconductor Corporation
Page 3 of 14
10/29/02
OPTICALLY ISOLATED
ERROR AMPLIFIER
FOD2741A
FOD2741B
FOD2741C
OUTPUT CHARACTERISTICS
(T
A
= 25°C Unless otherwise specified.)
Parameter
Collector dark current
Emitter-collector voltage breakdown
Collector-emitter voltage breakdown
Test Conditions
(V
CE
= 10 V) (Fig. 5)
(I
E
= 100 µA)
(I
C
= 1.0mA)
Symbol
I
CEO
BV
ECO
BV
CEO
7
70
Min
Typ
Max
50
Unit
nA
V
V
TRANSFER CHARACTERISTICS
(T
A
= 25°C Unless otherwise specified.)
Parameter
Current transfer ratio
Collector-emitter
saturation voltage
Test Conditions
(I
LED
= 10 mA, V
COMP
= V
FB
,
V
CE
= 5 V) (Fig. 6)
Symbol
CTR
Min
100
Typ
Max
200
0.4
Unit
%
V
(I
LED
= 10 mA, V
COMP
= V
FB,
V
CE (SAT)
I
C
= 2.5 mA) (Fig. 6)
ISOLATION CHARACTERISTICS
(T
A
= 25°C Unless otherwise specified.)
Parameter
Input-output insulation
leakage current
Withstand insulation
voltage
Resistance (input to output)
Test Conditions
(RH = 45%, T
A
= 25°C, t = 5s,
V
I-O
= 3000 VDC) (note. 1)
(RH <= 50%, T
A
= 25°C, t = 1 min)
(notes. 1)
V
I-O
= 500 VDC (note. 1)
Symbol
I
I-O
V
ISO
R
I-O
5000
10
12
Min
Typ
Max
1.0
Unit
µA
Vrms
Ohm
SWITCHING CHARACTERISTICS
(T
A
= 25°C Unless otherwise specified.)
Parameter
Bandwidth
Common mode transient
immunity at output high
Common mode transient
immunity at output low
Test Conditions
(Fig. 7)
(I
LED
= 0 mA,
Vcm
= 10 V
PP
RL = 2.2 kΩ (Fig. 8) (note. 2)
(I
LED
= 10 mA,
Vcm
= 10 V
PP
RL = 2.2 kΩ (Fig. 8) (note. 2)
Symbol
BW
CMH
CML
Min
Typ
10
1.0
1.0
Max
Unit
kHZ
kV/µs
kV/µs
Notes
1. Device is considered as a two terminal device: Pins 1,2 3 and 4 are shorted together and Pins 5,6,7 and 8 are shorted together.
2. Common mode transient immunity at output high is the maximum tolerable (positive) dVcm/dt on the leading edge of the com-
mon mode impulse signal, Vcm, to assure that the output will remain high. Common mode transient immunity at output low is
the maximum tolerable (negative) dVcm/dt on the trailing edge of the common pulse signal,Vcm, to assure that the output will
remain low.
© 2002 Fairchild Semiconductor Corporation
Page 4 of 14
10/29/02
OPTICALLY ISOLATED
ERROR AMPLIFIER
FOD2741A
I
(LED)
8
V
F
6
V
7
V
REF
5
3
V
R1
6
7
V
COMP
R2
V
REF
5
3
2
8
2
FOD2741B
I
(LED)
FOD2741C
FIG. 1. V
REF
, V
F,
I
LED
(min) TEST CIRCUIT
FIG. 2.
∆V
REF/
∆V
COMP
TEST CIRCUIT
I
(LED)
8
2
I
(OFF)
8
2
I
REF
6
V
R1
5
5
7
3
V
6
V
(LED)
7
3
FIG. 3. I
REF
TEST CIRCUIT
FIG. 4. I
(OFF)
TEST CIRCUIT
8
I
CEO
2
V
CE
I
(LED)
8
2
V
CE
6
V
7
V
COMP
V
REF
3
I
C
6
7
3
5
5
FIG. 5. I
CEO
TEST CIRCUIT
FIG. 6. CTR, V
CE(sat)
TEST CIRCUIT
© 2002 Fairchild Semiconductor Corporation
Page 5 of 14
10/29/02
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