Fairchild FOD2742A service manual
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
1 NC Not connected
2 C Phototransistor Collector
3 E Phototransistor Emitter
4 NC Not connected
5 GND Ground
6 COMP Error Amplifier Compensation. This pin is the output of the error amplifier. *
7 FB Voltage 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
Page 1 of 13
12/9/04
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
Transistor 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
Page 2 of 13
12/9/04
/ ∆
∆
∆
/ ∆
∆
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
Page 3 of 13
12/9/04
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 50 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
Page 4 of 13
12/9/04
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
Page 5 of 13
TEST CIRCUIT
CE(sat)
12/9/04
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