FOD2742A, FOD2742B, FOD2742C — Optically Isolated Error Amplifier
December 2008
FOD2742A, FOD2742B, FOD2742C
Optically Isolated Error Amplifier
Features
■
Optocoupler, precision reference and error amplifier in
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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.
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
Schematic
Package Outline
NC 1
8 LED
C 2
7 FB
E 3
6 COMP
NC 4
5 GND
©2003 Fairchild Semiconductor Corporation
FOD2742A, FOD2742B, FOD2742C Rev. 1.0.0
www.fairchildsemi.com
FOD2742A, FOD2742B, FOD2742C — 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
Functional Description
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.
Typical Application
V
1
FAN4803
PWM
Control
V
O
FOD2742
2
8
6
R1
3
7
R2
5
©2003 Fairchild Semiconductor Corporation
FOD2742A, FOD2742B, FOD2742C Rev. 1.0.0
www.fairchildsemi.com
2
FOD2742A, FOD2742B, FOD2742C — 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
V
LED
I
LED
V
CEO
V
ECO
I
C
PD1
PD2
PD3
Parameter
Storage Temperature
Operating Temperature
Reflow Temperature Profile (refer to page 14)
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
-25 to +85
Units
°C
°C
37
20
70
7
50
145
85
145
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.
©2003 Fairchild Semiconductor Corporation
FOD2742A, FOD2742B, FOD2742C Rev. 1.0.0
www.fairchildsemi.com
3
FOD2742A, FOD2742B, FOD2742C — 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
(Fig. 1)
Device Min.
All
A
B
C
2.482
2.470
2.450
Typ.
1.20
2.495
2.495
2.500
3.5
-0.5
-0.3
Max. Unit
1.5
2.508
2.520
2.550
17
-2.7
-2.0
4
1.2
1.0
1.0
0.5
V
V
V
V
mV
mV/
V
µA
µA
mA
µA
Ω
V
REF (DEV)
Deviation of V
REF
Over
Temperature
∆
V
RE
∆
V
COMP
I
REF
I
REF (DEV)
I
LED (MIN)
I
(OFF)
|Z
OUT
|
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)
T
A
= -25°C to +85°C (Fig. 1)
I
LED
= 10mA
(Fig. 2)
∆
V
COMP
= 10V to V
REF
∆
V
COMP
= 36V to 10V
All
All
I
LED
= 10mA, R
1
= 10K
Ω
(Fig. 3)
T
A
= -25°C to +85°C (Fig. 3)
V
COMP
= V
FB
(Fig. 1)
V
LED
= 37V, V
FB
= 0 (Fig. 4)
V
COMP
= V
REF
, I
LED
= 1mA to 20mA,
f
≥
1.0kHz
All
All
All
All
All
2.2
1.0
0.45
0.01
0.15
Notes:
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
©2003 Fairchild Semiconductor Corporation
FOD2742A, FOD2742B, FOD2742C Rev. 1.0.0
www.fairchildsemi.com
4
FOD2742A, FOD2742B, FOD2742C — Optically Isolated Error Amplifier
Electrical Characteristics
(T
A
= 25°C unless otherwise specified) (Continued)
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.
1
10
120
Max.
50
Unit
nA
V
V
Transfer Characteristics
Symbol
CTR
V
CE (SAT)
Parameter
Current Transfer Ratio
Collector-Emitter
Saturation Voltage
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.
140
0.16
Max.
200
0.4
Unit
%
V
Isolation Characteristics
Symbol
I
I-O
V
ISO
R
I-O
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. (Note 1)
V
I-O
= 500 VDC (Note 1)
Min.
Typ.
Max.
1.0
Unit
µA
Vrms
2500
10
12
Ω
Switching Characteristics
Symbol
B
W
CMH
CML
Parameter
Bandwidth
Common Mode Transient
Immunity at Output HIGH
Common Mode Transient
Immunity at Output LOW
Fig. 7
Test Conditions
I
LED
= 0mA,
V
cm
= 10 V
PP
RL = 2.2kΩ (Fig. 8) (Note 2)
I
LED
= 10mA,
V
cm
= 10 V
PP
RL = 2.2kΩ (Fig. 8) (Note 2)
Min.
Typ.
50
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 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
FOD2742A, FOD2742B, FOD2742C Rev. 1.0.0
www.fairchildsemi.com
5
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