Fairchild FOD2741A, FOD2741B, FOD2741C service manual

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%.

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.

OPTICALLY ISOLATED

ERROR AMPLIFIER

8

1

8

1

8

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%

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.

FUNCTIONAL BLOCK DIAGRAM

NC

1

C

2

E

3

NC

4 5

8

7

6

LED

FB

COMP

GND

* 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

FAN4803

V

1

PWM

Control

FOD2741

V

O

2

3

ABSOLUTE MAXIMUM RATINGS

Parameter Symbol Value Units

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) 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

T

V

V

V

STG

OPR

SOL

LED

I

LED

CEO

ECO

8

6

7

5

-55 to +125 °C

-25 to +85 °C

260 for 10 sec. °C

37 V

20 mA

30 V

7V

I

C

50 mA

R1

R2

© 2003 Fairchild Semiconductor Corporation

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12/9/04

/ ∆

∆

∆

/ ∆

∆

OPTICALLY ISOLATED

ERROR AMPLIFIER

FOD2741A FOD2741B FOD2741C

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

= 10 mA

I

LED

= V

COMP

I

= 10 mA, V

LED

V

= 10mA, R

V

= 37V, V

LED

, I

REF

= V

COMP

T

= -25°C to +85°CV

A

COMP

V

COMP

1

= -25°C to +85°CI

T

A

V

COMP

= 1mA to 20mA,

LED

) (fig.1) V

FB

= V

COMP

= 10V to V

FB

REF

= 36V to 10V

= 10k Ω (fig 3) I

= V

(fig.1) I

FB

= 0 (fig 4.) I

FB

f ≥ 1.0 kHz

F

V

REF

REF (DEV)

V

REF

V

COMP

REF

REF (DEV)

LED (MIN)

(OFF)

|

|Z

OUT

ALL 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 4.5 17 mV

ALL

-1.0 -2.7

-0.5 -2.0

mV/

V

ALL 1.5 4 µA

ALL 0.4 1.2 µA

ALL 0.45 1.0 mA

ALL 0.05 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 (see

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
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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12/9/04

OPTICALLY ISOLATED

ERROR AMPLIFIER

FOD2741A FOD2741B FOD2741C

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

50 nA

7V

70 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

V

CE

= 10 mA, V

I

= 2.5 mA) (Fig. 6)

C

(T

= 25°C Unless otherwise specified.)

A

= V

COMP

FB

= 5 V) (Fig. 6)

= V

COMP

FB,

,

CTR 100 200 %

V

CE

(SAT)

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

(notes. 1)

= 500 VDC (note. 1) R

I

I-O

V

ISO

I-O

5000 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 kΩ (Fig. 8) (note. 2)

(I

= 10 mA, Vcm = 10 V

LED

RL = 2.2 kΩ (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 15

12/9/04

OPTICALLY ISOLATED

ERROR AMPLIFIER

FOD2741A FOD2741B FOD2741C

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 15

TEST CIRCUIT

CE(sat)

12/9/04