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FOD2742A FOD2742B FOD2742C
DESCRIPTION
The FOD2742 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 converters.
When using the FOD2742, 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 small outline package.
FEATURES
OPTICALLY ISOLATED
ERROR AMPLIFIER
FUNCTIONAL BLOCK DIAGRAM
NC
1
LED
8
• Optocoupler, precision reference and error amplifier in single package
• 2.5V reference
• CTR 100% to 200%
• 2,500V RMS isolation
• UL approval E90700, Volume 2 • BSI approval 8661, 8662
• VDE approval 136616 • CSA approval 1113643
•Low temperature coefficient 50 ppm/°C max
• FOD2742A: tolerance 0.5%
FOD2742B: tolerance 1%
FOD2742C: tolerance 2%
APPLICATIONS
•Power supplies regulation
• DC to DC converters
PIN DEFINITIONS
Pin Number Pin Name Pin function description
1NCNot connected
2CPhototransistor Collector
3EPhototransistor Emitter
4NCNot connected
5 GND Ground
6 COMP Error Amplifier Compensation. This pin is the output of the error amplifier. *
7FBVoltage Feedback. This pin is the inverting input to the error amplifier
8 LED Anode LED. This pin is the input to the light emitting diode.
C
2
E
3
NC
4 5
7
6
FB
COMP
GND
* The compensation network must be attached between pins 6 and 7.
© 2003 Fairchild Semiconductor Corporation
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OPTICALLY ISOLATED
ERROR AMPLIFIER
FOD2742A FOD2742B FOD2742C
TYPICAL APPLICATION
FAN4803
V
1
PWM
Control
FOD2742
V
O
2
3
ABSOLUTE MAXIMUM RATINGS
Parameter Symbol Value Units
Storage Temperature
Operating Temperature
Reflow Temperature Profile (refer to fig. 21)
Input Voltage
Input DC Current
Collector-Emitter Voltage
Emitter-Collector Voltage
Collector Current
Input Power Dissipation (note 1) PD1 145 mW
Tr ansistor Power Dissipation (note 2) PD2 85 mW
Total Power Dissipation (note 3) PD3 145 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.
(T
= 25°C Unless otherwise specified.)
A
T
T
V
I
V
V
STG
OPR
LED
LED
CEO
ECO
I
C
8
6
7
5
-40 to +125 °C
-25 to +85 °C
37 V
20 mA
70 V
7V
50 mA
R1
R2
© 2003 Fairchild Semiconductor Corporation
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/ ∆
∆
∆
/ ∆
∆
OPTICALLY ISOLATED
ERROR AMPLIFIER
FOD2742A FOD2742B FOD2742C
ELECTRICAL CHARACTERISTICS
(T
= 25°C Unless otherwise specified.)
A
INPUT CHARACTERISTICS
Parameter Test Conditions Symbol Device Min. Typ. Max. Unit
(I
LED Forward Voltage
Reference Voltage
Deviation of V
REF
over
temperature
Ratio of V
variation to the
REF
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
V
= 10 mA, V
LED
I
= 10 mA, V
LED
= 10 mA
(fig. 2)
I
LED
= V
COMP
T
= -25°C to +85°C (fig. 1) V
A
V
= 10mA, R
= -25°C to +85°C (fig. 3) I
T
A
V
= 37V, V
LED
, I
REF
= V
COMP
COMP
COMP
V
COMP
= 10K Ω (fig. 3) I
1
V
COMP
= 1mA to 20mA,
LED
) (fig. 1) V
FB
= V
(fig. 1) V
FB
= 10V to V
= 36V to 10V
= V
(fig. 1) I
FB
= 0 (fig. 4) I
FB
f ≥ 1.0 kHz
REF
F
REF
REF (DEV)
V
REF
V
COMP
REF
REF (DEV)
LED (MIN)
(OFF)
|
|Z
OUT
ALL 1.20 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
ALL 3.5 17 mV
ALL
-0.5 -2.7
-0.3 -2.0
mV/
V
ALL 2.2 4 µA
ALL 1.0 1.2 µA
ALL 0.45 1.0 mA
ALL 0.01 1.0 µA
ALL 0.15 0.5 Ω
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
is defined as:
A
OUT
25°C=(){}106×
| = ∆ V
COMP
I
. When the device is operating with two external resistors
LED
V
∆V
REF
where ∆ T
ppm/°C()
is the rated operating free-air temperature range of the device.
A
REF DEV()/VREFTA
-----------------------------------------------------------------------------------------------------=
∆T
2. The dynamic impedance is defined as |Z
(see Figure 2), the total dynamic impedance of the circuit is given by:
Z
OUT, TOT
∆V
=
--------Z
∆I
OUT
R1
1
--------+×≈
R2
REF
,
© 2003 Fairchild Semiconductor Corporation
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OPTICALLY ISOLATED
ERROR AMPLIFIER
FOD2742A FOD2742B FOD2742C
OUTPUT CHARACTERISTICS
(T
= 25°C Unless otherwise specified.)
A
Parameter Test Conditions Symbol Min Typ Max Unit
(V
Collector dark current
Emitter-collector voltage breakdown
Collector-emitter voltage breakdown
TRANSFER CHARACTERISTICS
(T
= 10 V) (Fig. 5) I
CE
(I
= 100 µA) BV
E
(I
= 1.0mA) BV
C
= 25°C Unless otherwise specified.)
A
CEO
ECO
CEO
150nA
710 V
70 120 V
Parameter Test Conditions Symbol Min Typ Max Unit
(I
(I
LED
LED
Current transfer ratio
Collector-emitter
saturation voltage
ISOLATION CHARACTERISTICS
= 10 mA, V
= 5 V) (Fig. 6)
V
CE
= 10 mA, V
I
= 2.5 mA) (Fig. 6)
C
(T
= 25°C Unless otherwise specified.)
A
COMP
COMP
= V
= V
,
FB
CTR 100 140 200 %
FB,
V
CE
(SAT)
0.16 0.4 V
Parameter Test Conditions Symbol Min Typ Max Unit
Input-output insulation
leakage current
Withstand insulation
voltage
Resistance (input to output)
(RH = 45%, T
V
= 3000 VDC) (note. 1)
I-O
(RH <= 50%, T
V
I-O
= 25°C, t = 5s,
A
= 25°C, t = 1 min)
A
(note 1)
= 500 VDC (note 1) R
I
I-O
V
ISO
I-O
2500 Vrms
12
10
1.0 µA
Ohm
SWITCHING CHARACTERISTICS (T
= 25°C Unless otherwise specified.)
A
Parameter Test Conditions Symbol Min Typ Max Unit
Bandwidth (Fig. 7) BW 10 kHZ
(I
Common mode transient
immunity at output high
Common mode transient
immunity at output low
= 0 mA, Vcm = 10 V
LED
RL = 2.2 kV (Fig. 8) (note 2)
(I
= 10 mA, Vcm = 10 V
LED
RL = 2.2 kV (Fig. 8) (note 2)
PP
CMH 1.0 kV/µs
PP
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
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OPTICALLY ISOLATED
ERROR AMPLIFIER
FOD2742A FOD2742B FOD2742C
I
I
(LED)
V
82
V
F
6
7
V
REF
5
3
V
R2
(LED)
8
6R1
7
V
COMP
V
REF
5
2
3
FIG. 1. V
V
, VF, I
REF
FIG. 3. I
8
6
7
5
(min) TEST CIRCUIT
LED
I
(LED)
8
I
REF
6
7
R1
5
TEST CIRCUIT
REF
2
V
3
CE
I
CEO
FIG. 2. ∆V
2
3
V
REF/∆VCOMP
I
(OFF)
V
(LED)
FIG. 4. I
I
(LED)
V
TEST CIRCUIT
(OFF)
8
6
7
V
REF
5
8
6
7
5
TEST CIRCUIT
V
COMP
2
3
I
(C)
2
V
CE
3
FIG. 5. I
TEST CIRCUIT FIG. 6. CTR, V
CEO
© 2003 Fairchild Semiconductor Corporation
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TEST CIRCUIT
CE(sat)
8/27/03
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OPTICALLY ISOLATED
ERROR AMPLIFIER
FOD2742A FOD2742B FOD2742C
VCC = +5V DC
= 10 mA
I
F
R
L
V
OUT
1
2
3
4
8
7
0.1 V
PP
6
5
1µf
47Ω
V
IN
0.47V
Fig. 7 Frequency Response Test Circuit
= +5V DC
V
CC
I
= 0 mA (A)
F
IF = 10 mA (B)
R1
2.2kΩ
1
8
V
OUT
© 2003 Fairchild Semiconductor Corporation
2
3
4
VCM
_
10V
+
P-P
7
6
5
Fig. 8 CMH and CML Test Circuit
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A
B
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OPTICALLY ISOLATED
ERROR AMPLIFIER
FOD2742A FOD2742B FOD2742C
TYPICAL PERFORMANCE CURVES
- Reference Voltage (V)
REF
V
15
TA = 25°C
= V
V
COMP
10
5
0
-5
- Supply Current (mA)
LED
I
-10
-15
-1 0 1 2
FB
- Cathode Voltage (V)
V
COMP
Fig. 10 – Reference Voltage vs. Ambient Temperature
2.510
I
= 10mA
LED
2.508
2.506
2.504
2.502
2.500
2.498
2.496
2.494
2.492
2.490
Fig. 9a – LED Current vs. Cathode Voltage
-40 -20 0 20 40 60 80 100
T
- Ambient Temperature (°C)
A
1.0
0.5
0.0
- Supply Current (mA)
LED
-0.5
I
3
-1.0
Fig. 9b – LED Current vs. Cathode Voltage
= 25°C
T
A
= V
V
COMP
FB
-1 0 1 2
- Cathode Voltage (V)
V
COMP
3
Fig. 11 – Reference Current vs Ambient Temperature
I
= 10mA
LED
R1 = 10kΩ
3
- Reference Current (µA)
REF
2
I
-40 -20 0 20 40 60 80 100
- Ambient Temperature (°C)
T
A
Fig. 12 – Off-State Current vs. Ambient Temperature
V
= 37V
LED
100
10
- Off-state Current (nA)
OFF
I
1
-40 -20 0 20 40 60 80 100
TA - Ambient Temperature (°C)
© 2003 Fairchild Semiconductor Corporation
Page 7 of 13
Fig. 13 – Forward Current vs. Forward Voltage
20
15
10
- Forward Current (mA)
F
I
5
0.9 1.0 1.1 1.2
70°C
VF - Forward Voltage (V)
25°C
0°C
1.3 1.4
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OPTICALLY ISOLATED
ERROR AMPLIFIER
FOD2742A FOD2742B FOD2742C
TYPICAL PERFORMANCE CURVES
Fig. 14 – Dark Current vs. Ambient Temperature
VCE = 10V
1000
100
10
- Dark Current (nA)
CEO
I
1
0.1
-40 -20 0 20 40 60 80 100
T
- Ambient Temperature (°C)
A
Fig. 15 – Collector Current vs. Ambient Temperature
30
VCE = 5V
25
20
15
10
IC - Collector Current (mA)
5
0
0102030405060708090100
I
= 20mA
LED
I
= 10mA
LED
I
= 5mA
LED
I
= 1mA
LED
TA - Ambient Temperature (°C)
Fig. 16 – Current Transfer Ratio vs. LED Current
160
VCE = 5V
140
120
100
80
) - Current Transfer Ratio (%)
F
/I
C
60
(I
40
110100
I
LED
0°C
25°C
70°C
- Forward Current (mA)
Fig. 18 – Collector Current vs. Collector Voltage
35
TA = 25°C
30
25
20
15
10
- Collector Current (mA)
C
I
5
0
012345678910
- Collector-Emitter Voltage (V)
V
CE
I
I
LED
LED
= 20mA
I
LED
I
LED
= 1mA
= 10mA
= 5mA
Fig. 17 – Saturation Voltage vs. Ambient Temperature
0.26
= 10mA
I
LED
= 2.5mA
I
C
0.24
0.22
0.20
0.18
0.16
- Saturation Voltage (V)
0.14
CE(sat)
V
0.12
0.10
-40 -20 0 20 40
- Ambient Temperature (°C)
T
A
Fig. 19 – Rate of Change Vref to Vout vs. Temperature
-0.22
-0.24
-0.26
-0.28
-0.30
-0.32
-0.34
-0.36
-0.38
Delta Vref / Delta Vout ( mV/V)
-0.40
-0.42
-0.44
-40 -20 0 20 40 60 80
Temperature - °C
60 80 100
100
© 2003 Fairchild Semiconductor Corporation
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OPTICALLY ISOLATED
ERROR AMPLIFIER
FOD2742A FOD2742B FOD2742C
TYPICAL PERFORMANCE CURVES
5
VCC=10V
IF=10mA
Fig. 20 – Voltage Gain vs. Frequency
0
-5
Voltage Gain - dB
-10
-15
110100 1000
RL = 1kΩ
Frequency - kHz
RL = 100Ω
RL = 500Ω
© 2003 Fairchild Semiconductor Corporation
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OPTICALLY ISOLATED
ERROR AMPLIFIER
FOD2742A FOD2742B FOD2742C
The FOD2742
The FOD2742 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.
Powering the Secondary Side
The LED pin in the FOD2742 powers the secondary side, and
in particular provides the current to run the LED. The actual
structure of the FOD2742 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.
Feedback
Output voltage of a converter is determined by selecting a
resistor divider from the regulated output to the FB pin. The
FOD2742 attempts to regulate its FB pin to the reference
voltage, 2.5V. The ratio of the two resistors should thus be:
R
TOP
-------------------------R
BOTTOM
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
R
should be:
TOP
V
OUT
----------------------------R
TOP
V
OUT
-------------- 1–=
V
REF
2.5–
1040µA>
Compensation
The compensation pin of the FOD2742 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.
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
The Photo-transistor is the output of the FOD2742. In a normal
configuration the collector will be attached to a pull-up resistor
and the emitter grounded. There is no base connection necessary.
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.
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 10KV 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
R
COLLECTOR
COLLECTOR
6.25KΩ;><
© 2003 Fairchild Semiconductor Corporation
select 12KΩ to allow some margin.
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OPTICALLY ISOLATED
0.024 (0.61)
0.050 (1.27)
0.155 (3.94)
0.275 (6.99)
0.060 (1.52)
ERROR AMPLIFIER
FOD2742A FOD2742B FOD2742C
Package Dimensions
0.164 (4.16)
0.144 (3.66)
1
0.202 (5.13)
0.182 (4.63)
NG PLANE
SEATI
0.143 (3.63)
0.123 (3.13)
0.021 (0.53)
0.011 (0.28)
0.008 (0.20)
0.003 (0.08)
0.050 (1.27)
TYP
Lead Coplanarity : 0.004 (0.10) MAX
0.244 (6.19)
0.224 (5.69)
0.010 (0.25)
0.006 (0.16)
ORDERING INFORMATION
Option Order Entry Identifier Description
Footprint Drawing
R1 R1 Tape and reel (500 units per reel)
R1V R1V VDE0884, Tape and reel (500 units per reel)
R2 R2 Tape and reel (2,500 units per reel)
R2V R2V VDE0884, Tape and reel (2,500 units per reel)
MARKING INFORMATION
1
43
2742A
5
SYYXV
Definitions
2
6
1Fairchild logo
2Device number
VDE mark (Note: Only appears on parts ordered with VDE
3
option – See order entry table)
4 One digit year code
5Two digit work week ranging from ‘01’ to ‘53’
6 Assembly package code
© 2003 Fairchild Semiconductor Corporation
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OPTICALLY ISOLATED
ERROR AMPLIFIER
FOD2742A FOD2742B FOD2742C
Carrier Tape Specifications
8.0 ± 0.10
3.50 ± 0.20
8.3 ± 0.10
0.30 MAX
2.0 ± 0.05
4.0 ± 0.10
Ø1.5 MIN
1.75 ± 0.10
5.5 ± 0.05
12.0 ± 0.3
5.20 ± 0.20
Reflow Profile
300
250
200
150
100
Temperature (°C)
50
0
0
0.1 MAX
User Direction of Feed
230°C, 10–30 s
245°C peak
Time above 183°C, 120–180 sec
Ramp up = 2–10°C/sec
0.5 1 1.5 2 2.5 3 3.5 4 4.5
Time (Minute)
6.40 ± 0.20
Ø1.5 ± 0.1/-0
• Peak reflow temperature: 245°C (package surface temperature)
• Time of temperature higher than 183°C for 120–180 seconds
• One time soldering reflow is recommended
© 2003 Fairchild Semiconductor Corporation
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OPTICALLY ISOLATED
ERROR AMPLIFIER
FOD2742A FOD2742B FOD2742C
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.
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.
© 2003 Fairchild Semiconductor Corporation
Page 13 of 13
8/27/03
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