OPTICALLY ISOLATED
ERROR AMPLIFIER
FOD2741A
FOD2741B
FOD2741C
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%.
8
1
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 converters.
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
8
1
1
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
Pin Name
Pin function description
1
NC
2
C
Phototransistor Collector
3
E
Phototransistor Emitter
4
NC
5
GND
6
COMP
7
FB
8
LED
Not connected
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.
© 2003 Fairchild Semiconductor Corporation
Page 1 of 15
12/9/04
OPTICALLY ISOLATED
ERROR AMPLIFIER
FOD2741A
FOD2741B
FOD2741C
TYPICAL APPLICATION
V1
FAN4803
PWM
Control
VO
FOD2741
2
8
6
3
R1
7
R2
5
ABSOLUTE MAXIMUM RATINGS (TA = 25°C Unless otherwise specified.)
Parameter
Symbol
Value
Units
Storage Temperature
TSTG
-55 to +125
°C
Operating Temperature
TOPR
-25 to +85
°C
Lead Solder Temperature
TSOL
260 for 10 sec.
°C
Input Voltage
VLED
37
V
Input DC Current
ILED
20
mA
Collector-Emitter Voltage
VCEO
30
V
Emitter-Collector Voltage
VECO
7
V
Collector Current
Input Power Dissipation (note 1)
Transistor Power Dissipation (note 2)
Total Power Dissipation (note 3)
IC
50
mA
PD1
PD2
PD3
145
85
145
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.
© 2003 Fairchild Semiconductor Corporation
Page 2 of 15
12/9/04
OPTICALLY ISOLATED
ERROR AMPLIFIER
FOD2741A
FOD2741B
FOD2741C
ELECTRICAL CHARACTERISTICS (TA = 25°C Unless otherwise specified.)
INPUT CHARACTERISTICS
Parameter
Test Conditions
(ILED = 10 mA, VCOMP = VFB) (fig.1)
LED Forward Voltage
ILED = 10 mA, VCOMP = VFB
Reference Voltage
Deviation of VREF over
temperature
Ratio of VREF variation to the
output of the error amplifier
Symbol
Device
VF
ALL
VREF
TA = -25°C to +85°C VREF (DEV)
ILED = 10 mA
∆VCOMP = 10V to VREF
∆VCOMP = 36V to 10V
ILED = 10mA, R1 = 10kΩ (fig 3)
Feedback Input Current
Min.
Typ.
Max.
Unit
1.5
V
A
2.482
2.495
2.508
V
B
2.470
2.495
2.520
V
C
2.450
2.500
2.550
V
4.5
17
mV
-1.0
-2.7
-0.5
-2.0
mV/
V
ALL
∆VREF/
∆VCOMP
ALL
IREF
ALL
1.5
4
µA
Deviation of IREF over
temperature
TA = -25°C to +85°C
IREF (DEV)
ALL
0.4
1.2
µA
Minimum Drive Current
VCOMP = VFB (fig.1)
ILED (MIN)
ALL
0.45
1.0
mA
VLED = 37V, VFB = 0 (fig 4.)
I(OFF)
ALL
0.05
1.0
µA
VCOMP = VREF, ILED = 1mA to 20mA,
f ≥ 1.0 kHz
|ZOUT|
ALL
0.15
0.5
Ω
Off-state error amplifier current
Error amplifier output impedance
(see note 2)
1. The deviation parameters VREF(DEV) and IREF(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, ∆VREF,
is defined as:
6
{ V REF ( DEV ) /V REF ( T A = 25°C ) } × 10
∆V REF ( ppm/°C ) = ----------------------------------------------------------------------------------------------------∆T A
where ∆TA is the rated operating free-air temperature range of the device.
2. The dynamic impedance is defined as |ZOUT| = ∆VCOMP/∆ILED. 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
© 2003 Fairchild Semiconductor Corporation
Page 3 of 15
12/9/04
OPTICALLY ISOLATED
ERROR AMPLIFIER
FOD2741A
FOD2741B
FOD2741C
OUTPUT CHARACTERISTICS (TA = 25°C Unless otherwise specified.)
Parameter
Test Conditions
(VCE = 10 V) (Fig. 5)
Collector dark current
Symbol
Min
Typ
ICEO
Max
Unit
50
nA
Emitter-collector voltage breakdown
(IE = 100 µA)
BVECO
7
V
Collector-emitter voltage breakdown
(IC = 1.0mA)
BVCEO
70
V
TRANSFER CHARACTERISTICS (TA = 25°C Unless otherwise specified.)
Parameter
Test Conditions
Symbol
Min
CTR
100
Current transfer ratio
(ILED = 10 mA, VCOMP = VFB,
VCE = 5 V) (Fig. 6)
Collector-emitter
saturation voltage
(ILED = 10 mA, VCOMP = VFB,
VCE (SAT)
IC = 2.5 mA) (Fig. 6)
Typ
Max
Unit
200
%
0.4
V
Max
Unit
1.0
µA
ISOLATION CHARACTERISTICS (TA = 25°C Unless otherwise specified.)
Parameter
Test Conditions
(RH = 45%, TA = 25°C, t = 5s,
VI-O = 3000 VDC) (note. 1)
Input-output insulation
leakage current
Withstand insulation
voltage
Symbol
Typ
II-O
(RH <= 50%, TA = 25°C, t = 1 min)
(notes. 1)
VISO
VI-O = 500 VDC (note. 1)
RI-O
Resistance (input to output)
Min
5000
Vrms
1012
Ohm
SWITCHING CHARACTERISTICS (TA = 25°C Unless otherwise specified.)
Parameter
Test Conditions
Bandwidth
(Fig. 7)
Symbol
Min
Typ
Max
Unit
BW
50
kHZ
Common mode transient
immunity at output high
(ILED = 0 mA, Vcm = 10 VPP
RL = 2.2 kΩ (Fig. 8) (note. 2)
CMH
1.0
kV/µs
Common mode transient
immunity at output low
(ILED = 10 mA, Vcm = 10 VPP
RL = 2.2 kΩ (Fig. 8) (note. 2)
CML
1.0
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 common 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.
© 2003 Fairchild Semiconductor Corporation
Page 4 of 15
12/9/04
OPTICALLY ISOLATED
ERROR AMPLIFIER
FOD2741A
FOD2741B
FOD2741C
I(LED)
I(LED)
8
8
2
2
VF
6
6
V
7
V
R1
3
3
7
VCOMP
R2
VREF
VREF
5
5
FIG. 2. ∆VREF/∆VCOMP TEST CIRCUIT
FIG. 1. VREF, VF, ILED (min) TEST CIRCUIT
I(LED)
I(OFF)
8
2
8
2
IREF
6
6
3
7
V
3
V(LED)
7
V
R1
5
5
FIG. 3. IREF TEST CIRCUIT
8
FIG. 4. I(OFF) TEST CIRCUIT
I(LED)
ICEO
8
2
VCE
6
VCE
6
3
7
IC
2
V
3
7
VCOMP
VREF
5
5
FIG. 5. ICEO TEST CIRCUIT
© 2003 Fairchild Semiconductor Corporation
FIG. 6. CTR, VCE(sat) TEST CIRCUIT
Page 5 of 15
12/9/04
OPTICALLY ISOLATED
ERROR AMPLIFIER
FOD2741A
FOD2741B
FOD2741C
VCC = +5V DC
IF = 10 mA
RL
47Ω
8
1
1µf
VOUT
7
2
VIN
0.47V
0.1 VPP
3
6
4
5
Fig. 7 Frequency Response Test Circuit
VCC = +5V DC
IF = 0 mA (A)
IF = 10 mA (B)
R1
2.2kΩ
VOUT
1
8
2
7
3
6
4
5
_
A B
VCM
+
10VP-P
Fig. 8 CMH and CML Test Circuit
© 2003 Fairchild Semiconductor Corporation
Page 6 of 15
12/9/04
OPTICALLY ISOLATED
ERROR AMPLIFIER
FOD2741A
FOD2741B
FOD2741C
TYPICAL PERFORMANCE CURVES
Fig. 9a – LED Current vs. Cathode Voltage
15
Fig. 9b – LED Current vs. Cathode Voltage
1.0
TA = 25°C
VCOMP = VFB
TA = 25°C
VCOMP = VFB
ILED - Supple Current (mA)
ILED - Supple Current (mA)
10
5
0
-5
0.5
0.0
-0.5
-10
-15
-1.0
-1
0
1
3
2
-1
0
VCOMP - Cathode Voltage (V)
Fig. 10 – Reference Voltage vs. Ambient Temperature
2
3
Fig. 11 – Reference Current vs Ambient Temperature
2.510
1.30
ILED = 10mA
R1 = 10kΩ
ILED = 10mA
2.508
2.506
IREF - Reference Current (µA)
VREF - Reference Voltage (V)
1
VCOMP - Cathode Voltage (V)
2.504
2.502
2.500
2.498
2.496
2.494
1.25
1.20
1.15
1.10
2.492
2.490
-40
-20
0
20
40
60
80
100
1.05
-40
-20
0
20
40
60
80
100
TA - Ambient Temperature (°C)
TA - Ambient Temperature (°C)
Fig. 12 – Off-State Current vs. Ambient Temperature
Fig. 13 – Forward Current vs. Forward Voltage
20
100
IF - Forward Current (mA)
IOFF - Off-State Current (nA)
VCC = 37V
10
15
25°C
10
0°C
70°C
5
1
-40
-20
0
20
40
60
80
100
© 2003 Fairchild Semiconductor Corporation
0.9
1.0
1.1
1.2
1.3
1.4
VF - Forward Voltage (V)
TA - Ambient Temperature (°C)
Page 7 of 15
12/9/04
OPTICALLY ISOLATED
ERROR AMPLIFIER
FOD2741A
FOD2741B
FOD2741C
Fig. 15 – Collector Current vs. Ambient Temperature
Fig. 14 – Dark Current vs. Ambient Temperature
30
10000
VCE = 10V
VCE = 5V
25
IC - Collector Current (mA)
ICEO - Dark Current (nA)
1000
100
10
1
ILED = 20mA
20
15
ILED = 10mA
10
ILED = 6mA
5
ILED = 1mA
0
0.1
-40
-20
0
20
40
60
80
0
100
10
20
30
40
50
60
70
80
90
100
TA - Ambient Temperature (°C)
TA - Ambient Temperature (°C)
Fig. 16 – Current Transfer Ratio vs. LED Current
Fig. 17 – Saturation Voltage vs. Ambient Temperature
0.26
VCE = 5V
0.24
VCE(sat) - Saturation Voltage (V)
(IC/IF) - Current Transfer Ratio (%)
140
120
0°C
100
25°C
80
70°C
60
0.22
0.20
0.18
0.16
0.14
0.12
0.10
-40
40
0
5
10
15
20
25
30
35
ILED - Forward Current (mA)
40
45
50
-20
0
20
60
40
80
100
TA - Ambient Temperature (°C)
Fig. 19 – Rate of Change Vref to Vout vs. Temperature
Fig. 18 – Collector Current vs. Collector Voltage
-0.32
35
TA = 25°C
-0.34
Delta Vref / Delta Vout ( mV/V)
IC - Collector Current (mA)
30
ILED = 20mA
25
20
15
ILED = 10mA
10
ILED = 5mA
-0.36
-0.38
-0.40
-0.42
-0.44
5
ILED = 1mA
0
0
1
2
3
4
5
6
7
VCE - Collector-Emitter Voltage (V)
© 2003 Fairchild Semiconductor Corporation
8
9
10
-0.46
-60
-40
-20
0
20
40
60
80
100
120
Temperature - °C
Page 8 of 15
12/9/04
OPTICALLY ISOLATED
ERROR AMPLIFIER
FOD2741A
FOD2741B
FOD2741C
Fig. 20 – Voltage Gain vs. Frequency
VCC=10V
IF=10mA
Voltage Gain - dB
0
RL = 100Ω
-5
RL = 500Ω
RL = 1kΩ
-10
-15
0.1
© 2003 Fairchild Semiconductor Corporation
1
10
Frequency - kHz
Page 9 of 15
100
1000
12/9/04
OPTICALLY ISOLATED
ERROR AMPLIFIER
FOD2741A
FOD2741B
FOD2741C
The FOD2741
Compensation
The FOD2741 is an optically isolated error amplifier. It incorporates three of the most common elements necessary to
make an isolated power supply, a reference voltage, an error
amplifier, and an optocoupler. It is functionally equivalent to
the popular KA431 shunt voltage regulator plus the CNY17F-X
optocoupler.
The compensation pin of the FOD2741 provides the opportunity for the designer to design the frequency response of the
converter. A compensation network may be placed between
the COMP pin and the FB pin. In typical low-bandwidth
systems, a 0.1µF capacitor may be used. For converters with
more stringent requirements, a network should be designed
based on measurements of the system’s loop. An excellent
reference for this process may be found in “Practical Design of
Power Supplies” by Ron Lenk, IEEE Press, 1998.
Powering the Secondary Side
The LED pin in the FOD2741 powers the secondary side, and
in particular provides the current to run the LED. The actual
structure of the FOD2741 dictates the minimum voltage that
can be applied to the LED pin: The error amplifier output has a
minimum of the reference voltage, and the LED is in series
with that. Minimum voltage applied to the LED pin is thus 2.5V
+ 1.5V = 4.0V. This voltage can be generated either directly
from the output of the converter, or else from a slaved secondary winding. The secondary winding will not affect regulation,
as the input to the FB pin may still be taken from the output
winding.
The LED pin needs to be fed through a current limiting resistor.
The value of the resistor sets the amount of current through
the LED, and thus must be carefully selected in conjunction
with the selection of the primary side resistor.
Secondary Ground
The GND pin should be connected to the secondary ground of
the converter.
No Connect Pins
The NC pins have no internal connection. They should not
have any connection to the secondary side, as this may
compromise the isolation structure.
Photo-Transistor
Feedback
The Photo-transistor is the output of the FOD2741. In a normal
configuration the collector will be attached to a pull-up resistor
and the emitter grounded. There is no base connection necessary.
Output voltage of a converter is determined by selecting a
resistor divider from the regulated output to the FB pin. The
FOD2741 attempts to regulate its FB pin to the reference
voltage, 2.5V. The ratio of the two resistors should thus be:
The value of the pull-up resistor, and the current limiting resistor feeding the LED, must be carefully selected to account for
voltage range accepted by the PWM IC, and for the variation in
current transfer ratio (CTR) of the opto-isolator itself.
R TOP
V OUT
-------------------------- = -------------- – 1
R BOTTOM
V REF
The absolute value of the top resistor is set by the input offset
current of 5.2µA. To achieve 0.5% accuracy, the resistance of
RTOP should be:
V OUT – 2.5
----------------------------- > 1040µA
R TOP
Example: The voltage feeding the LED pins is +12V, the voltage feeding the collector pull-up is +10V, and the PWM IC is
the Fairchild KA1H0680, which has a 5V reference. If we
select a 10kΩ resistor for the LED, the maximum current the
LED can see is (12V-4V) /10kΩ = 800µA. The CTR of the
opto-isolator is a minimum of 100%, so the minimum collector
current of the photo-transistor when the diode is full on is also
800µA. The collector resistor must thus be such that:
10V – 5V
------------------------------------ < 800µA or R COLLECTOR > 6.25kΩ;
R COLLECTOR
select 12kΩ to allow some margin.
© 2003 Fairchild Semiconductor Corporation
Page 10 of 15
12/9/04
OPTICALLY ISOLATED
ERROR AMPLIFIER
FOD2741A
FOD2741B
Package Dimensions (Through Hole)
Package Dimensions (Surface Mount)
0.390 (9.91)
0.370 (9.40)
PIN 1
ID.
4
3
2
FOD2741C
4
3
2
1
0.270 (6.86)
0.250 (6.35)
5
6
7
PIN 1
ID.
1
0.270 (6.86)
0.250 (6.35)
8
5
6
8
7
SEATING PLANE
0.390 (9.91)
0.370 (9.40)
0.020 (0.51)
MIN
0.020 (0.51) MIN
0.200 (5.08)
0.140 (3.55)
0.154 (3.90)
0.120 (3.05)
0.022 (0.56)
0.016 (0.41)
0.016 (0.40)
0.008 (0.20)
0.100 (2.54) TYP
15° MAX
3
2
0.405 (10.30)
MIN
Lead Coplanarity : 0.004 (0.10) MAX
8 - Pin Dip
PIN 1
ID.
1
0.315 (8.00)
MIN
0.100 (2.54)
TYP
0.300 (7.62)
TYP
0.070 (1.78)
0.270 (6.86)
0.250 (6.35)
5
6
7
0.060 (1.52)
8
0.100 (2.54)
0.390 (9.91)
0.370 (9.40)
SEATING PLANE
0.016 (0.41)
0.008 (0.20)
0.045 [1.14]
0.022 (0.56)
0.016 (0.41)
Package Dimensions (0.4"Lead Spacing)
4
0.300 (7.62)
TYP
0.070 (1.78)
0.045 (1.14)
0.070 (1.78)
0.045 (1.14)
0.295 (7.49)
0.415 (10.54)
0.070 (1.78)
0.045 (1.14)
0.030 (0.76)
0.004 (0.10) MIN
0.200 (5.08)
0.140 (3.55)
0.154 (3.90)
0.120 (3.05)
0.022 (0.56)
0.016 (0.41)
0.016 (0.40)
0.008 (0.20)
0.100 (2.54) TYP
0° to 15°
0.400 (10.16)
TYP
NOTE
All dimensions are in inches (millimeters)
© 2003 Fairchild Semiconductor Corporation
Page 11 of 15
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OPTICALLY ISOLATED
ERROR AMPLIFIER
FOD2741A
FOD2741B
ORDERING INFORMATION
Example: FOD2741A
X
FOD2741C
Y
Y
X
Packaging Option
T: 0.4” Lead Spacing
S: Surface Mount Lead Bend
SD: Surface Mount Tape and Reel (1000 per reel)
V: VDE tested
MARKING INFORMATION
1
V
3
2741A
2
XX YY B
6
4
5
Definitions
1
Fairchild logo
2
Device number
3
VDE mark (Note: Only appears on parts ordered with VDE
option – See order entry table)
4
Two digit year code, e.g., ‘03’
5
Two digit work week ranging from ‘01’ to ‘53’
6
Assembly package code
© 2003 Fairchild Semiconductor Corporation
Page 12 of 15
12/9/04
OPTICALLY ISOLATED
ERROR AMPLIFIER
FOD2741A
FOD2741B
FOD2741C
Carrier Tape Specifications
P0
t
K0
P2
D0
E
F
A0
W1
W
B0
d
Description
Tape Width
Tape Thickness
P
User Direction of Feed
D1
Symbol
Dimension in mm
W
16.0 ± 0.3
t
0.30 ± 0.05
Sprocket Hole Pitch
P0
4.0 ± 0.1
Sprocket Hole Diameter
D0
1.55 ± 0.05
Sprocket Hole Location
E
1.75 ± 0.10
Pocket Location
Pocket Pitch
Pocket Dimensions
Cover Tape Width
Cover Tape Thickness
F
7.5 ± 0.1
P2
4.0 ± 0.1
P
12.0 ± 0.1
A0
10.30 ±0.20
B0
10.30 ±0.20
K0
4.90 ±0.20
W1
1.6 ± 0.1
d
0.1 max
Max. Component Rotation or Tilt
Min. Bending Radius
© 2003 Fairchild Semiconductor Corporation
10°
R
Page 13 of 15
30
12/9/04
OPTICALLY ISOLATED
ERROR AMPLIFIER
FOD2741A
FOD2741B
FOD2741C
Reflow Profile
245 C, 10–30 s
Temperature (°C)
300
260 C peak
250
200
150
Time above 183C, <160 sec
100
50
Ramp up = 2–10C/sec
0
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
Time (Minute)
• Peak reflow temperature: 260 C (package surface temperature)
• Time of temperature higher than 183 C for 160 seconds or less
• One time soldering reflow is recommended
© 2003 Fairchild Semiconductor Corporation
Page 14 of 15
12/9/04
OPTICALLY ISOLATED
ERROR AMPLIFIER
FOD2741A
FOD2741B
FOD2741C
DISCLAIMER
FAIRCHILD SEMICONDUCTOR RESERVES THE RIGHT TO MAKE CHANGES WITHOUT FURTHER NOTICE TO
ANY PRODUCTS HEREIN TO IMPROVE RELIABILITY, FUNCTION OR DESIGN. FAIRCHILD DOES NOT ASSUME
ANY LIABILITY ARISING OUT OF THE APPLICATION OR USE OF ANY PRODUCT OR CIRCUIT DESCRIBED HEREIN;
NEITHER DOES IT CONVEY ANY LICENSE UNDER ITS PATENT RIGHTS, NOR THE RIGHTS OF OTHERS.
LIFE SUPPORT POLICY
FAIRCHILD’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES
OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF FAIRCHILD SEMICONDUCTOR
CORPORATION. As used herein:
1. Life support devices or systems are devices or systems
which, (a) are intended for surgical implant into the body, or
(b) support or sustain life, and (c) whose failure to perform
when properly used in accordance with instructions for use
provided in the labeling, can be reasonably expected to
result in a significant injury of the user.
© 2003 Fairchild Semiconductor Corporation
2. A critical component in any component of a life support
device or system whose failure to perform can be
reasonably expected to cause the failure of the life support
device or system, or to affect its safety or effectiveness.
Page 15 of 15
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