Fairchild FOD2712A service manual

FOD2712A — Optically Isolated Error Amplifier

December 2010

FOD2712A
Optically Isolated Error Amplifier

Features

■

Optocoupler, precision reference and error amplifier in
single package

■

1.240V ± 1% reference

■

CTR 100% to 200%
2,500V RMS isolation

■

■

UL approval E90700

Applications

Power system for workstations

■

■

Telecom central office supply

■

Telecom bricks

Description

The FOD2712A Optically Isolated Amplifier consists of
the popular AZ431L precision programmable shunt ref­erence and an optocoupler. The optocoupler is a gallium
arsenide (GaAs) light emitting diode optically coupled to
a silicon phototransistor. The reference voltage toler­ance is 1%. The current transfer ratio (CTR) ranges from
100% to 200%.

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 FOD2712A, 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 compact 8-pin small outline
package.

Schematic Package Outline

1

NC

C

2

3

E

NC

4 5

©2010 Fairchild Semiconductor Corporation www.fairchildsemi.com
FOD2712A Rev. 1.0.1

8

7

6

LED

FB

COMP

GND

Pin Definitions

Pin Number Pin Name Functional 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.

*The compensation network must be attached between pins 6 and 7.

Typical Application

FOD2712A — Optically Isolated Error Amplifier

FAN4803

V

1

PWM

Control

FOD2712A

2

3

8

6

7

5

R1

R2

V

O

©2010 Fairchild Semiconductor Corporation www.fairchildsemi.com
FOD2712A Rev. 1.0.1 2

FOD2712A — Optically Isolated Error Amplifier

Absolute Maximum Ratings

(T

= 25°C unless otherwise specified)

A

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 Parameter Value Units

T

STG

T

OPR

V

LED

I

LED

V

CEO

V

ECO

I

C

PD1 Input Power Dissipation

PD2 Transistor Power Dissipation

PD3 Total Power Dissipation

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.

Storage Temperature -40 to +125 °C

Operating Temperature -40 to +85 °C

Reflow Temperature Profile (refer to 15)

Input Voltage 13.2 V

Input DC Current 20 mA

Collector-Emitter Voltage 30 V

Emitter-Collector Voltage 7 V

Collector Current 50 mA

(1)

(2)

(3)

145 mW

85 mW

145 mW

©2010 Fairchild Semiconductor Corporation www.fairchildsemi.com
FOD2712A Rev. 1.0.1 3

/ ∆

∆

∆

FOD2712A — Optically Isolated Error Amplifier

Electrical Characteristics

(V

= 12V, T

CC

= 25°C unless otherwise specified)

A

Input Characteristics

Symbol Parameter Test Conditions Min. Typ. Max. Unit

V

LED Forward Voltage I

F

= 10mA, V

LED

COMP

= V

FB

(Fig.1)

V

REF

V

REF (DEV)

Reference Voltage

-40°C to +85°C
25°C

Deviation of V

REF

over temperature

V

= V

, I

COMP

(Fig.1)

FB

LED

= 10mA

1.221 1.259 V

1.228 1.240 1.252

T

= -40 to +85°C 4 12 mV

A

See Note 1

V

V

COMP

I

REF

REF

Ratio of Vref Variation to the Output of the
Error Amplifier

Feedback Input Current I

I

= 10 mA,

LED

V

= V

COMP

REF

(Fig. 2)

= 10mA, R1 = 10k Ω

LED

-1.5 -2.7 mV/V

to 12V

0.15 0.5 µA

(Fig. 3)

I

REF (DEV)

Deviation of I

Over Temperature

REF

T

= -40 to +85°C 0.15 0.3 µA

A

See Note 1

I

LED (MIN)

I

(OFF)

|Z

OUT

Minimum Drive Current V

Off-state Error Amplifier Current V

| Error Amplifier Output Impedance

See Note 2

= V

COMP

= 6V, V

LED

V

COMP

I

= 0.1mA to 15mA,

LED

(Fig.1) 55 80 µA

FB

FB

= V

,

FB

= 0 (Fig.4) 0.001 0.1 µA

0.25

f < 1kHZ

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

∆V

REF

where ∆ T

ppm/°C()

is the rated operating free-air temperature range of the device.

A

V

-----------------------------------------------------------------------------------------------------=

2. The dynamic impedance is defined as |Z

, is defined as:

REF

REF DEV()/VREFTA

∆T

A

OUT

25°C=(){}106×

| = ∆ V

COMP

I

. When the device is operating with two external

LED

resistors (see Figure 2), the total dynamic impedance of the circuit is given by:

1.5 V

Ω

Z

OUT, TOT

©2010 Fairchild Semiconductor Corporation www.fairchildsemi.com
FOD2712A Rev. 1.0.1 4

∆V

=

--------Z

∆I

OUT

R1

1

--------+×≈
R2

FOD2712A — Optically Isolated Error Amplifier

Electrical Characteristics

(V

= 12V, T

CC

= 25°C unless otherwise specified) (Continued)

A

Output Characteristics

Symbol Parameter Test Conditions Min. Typ. Max. Unit

BV

BV

I

CEO

CEO

ECO

Collector Dark Current V

Collector-Emitter Voltage
Breakdown

Emitter-Collector Voltage
Breakdown

= 10V (Fig. 5) 50 nA

CE

I

= 1.0mA 70 V

C

I

= 100µA 7 V

E

Transfer Characteristics

Symbol Parameter Test Conditions Min. Typ. Max. Unit

CTR Current Transfer Ratio I

V

CE

Collector-Emitter

(SAT)

Saturation Voltage

= 10mA, V

LED

V

= 5V (Fig. 6)

CE

I

= 10mA, V

LED

I

= 2.5mA (Fig. 6)

C

COMP

COMP

= V

= V

FB

FB

,

,

100 200 %

0.4 V

Isolation Characteristics

Symbol Parameter Test Conditions Min. Typ. Max. Unit

I

I-O

V

ISO

R

I-O

Input-Output Insulation
Leakage Current

RH = 45%, T
V

= 3000 VDC (Note 1)

I-O

Withstand Insulation Voltage RH ≤ 50%, T

t = 1 min. (Note 1)

Resistance (Input to Output) V

= 500 VDC (Note 1) 10

I-O

= 25°C, t = 5s,

A

= 25°C,

A

1.0 µA

2500 Vrms

12

Ω

Switching Characteristics

Symbol Parameter Test Conditions Min. Typ. Max. Unit

B

W

CMH Common Mode Transient

CML Common Mode Transient

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.

©2010 Fairchild Semiconductor Corporation www.fairchildsemi.com
FOD2712A Rev. 1.0.1 5

Bandwidth Fig. 7 10 kHz

= 0mA, Vcm = 10 V

Immunity at Output HIGH

Immunity at Output LOW

I

LED

RL = 2.2kΩ (Fig. 8) (Note 2)

= 10mA, Vcm = 10 V

I

LED

RL = 2.2kΩ (Fig. 8) (Note 2)

PP

PP

1.0 kV/µs

1.0 kV/µs