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OPTICALLY ISOLATED ERROR AMPLIFIER FOD2742A
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.
FUNCTIONAL BLOCK DIAGRAM
FOD2742B
FOD2742C
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
* 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 * VDE approval 136616 * FOD2742A: tolerance 0.5% FOD2742B: tolerance 1% FOD2742C: tolerance 2% * BSI approval 8661, 8662 * CSA approval 1113643
NC
1
8 LED
C
2
7 FB
E
3
6 COMP
NC
4
5 GND
* Low temperature coefficient 50 ppm/C max
APPLICATIONS
* Power supplies regulation * DC to DC converters
PIN DEFINITIONS
Pin Number 1 2 3 4 5 6 7 8 Pin Name NC C E NC GND COMP FB LED Pin function description Not connected 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.
(c) 2003 Fairchild Semiconductor Corporation
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OPTICALLY ISOLATED ERROR AMPLIFIER FOD2742A
TYPICAL APPLICATION
FOD2742B
FOD2742C
V1
FAN4803 PWM Control
VO
FOD2742 2 8
6
R1
3
7 R2
5
ABSOLUTE MAXIMUM RATINGS (TA = 25C Unless otherwise specified.)
Parameter 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) Transistor Power Dissipation (note 2) Total Power Dissipation (note 3) VLED ILED VCEO VECO IC PD1 PD2 PD3 37 20 70 7 50 145 85 145 V mA V V mA mW mW mW Symbol TSTG TOPR Value -40 to +125 -25 to +85 Units C C
Notes 1. Derate linearly from 25C at a rate of 2.42 mW/ C 2. Derate linearly from 25C at a rate of 1.42 mW/ C. 3. Derate linearly from 25C 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.
(c) 2003 Fairchild Semiconductor Corporation
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OPTICALLY ISOLATED ERROR AMPLIFIER FOD2742A FOD2742B FOD2742C
ELECTRICAL CHARACTERISTICS (TA = 25C Unless otherwise specified.) INPUT CHARACTERISTICS
Parameter LED Forward Voltage Test Conditions (ILED = 10 mA, VCOMP = VFB) (fig. 1) ILED = 10 mA, VCOMP = VFB (fig. 1) Symbol VF VREF Device ALL A Reference Voltage Deviation of VREF over temperature Ratio of VREF variation to the output of the error amplifier Feedback Input Current Deviation of IREF over temperature Minimum Drive Current Off-state error amplifier current Error amplifier output impedance (see note 2) B C TA = -25C to +85C (fig. 1) VREF (DEV) ILED = 10 mA VCOMP = 10V to VREF (fig. 2) VCOMP = 36V to 10V ILED = 10mA, R1 = 10K (fig. 3) TA = -25C to +85C (fig. 3) VCOMP = VFB (fig. 1) VLED = 37V, VFB = 0 (fig. 4) VCOMP = VREF, ILED = 1mA to 20mA, f 1.0 kHz VREF/ VCOMP IREF IREF (DEV) ILED (MIN) I(OFF) |ZOUT| ALL ALL ALL ALL ALL ALL ALL 2.482 2.470 2.450 Min. Typ. 1.20 2.495 2.495 2.500 3.5 -0.5 -0.3 2.2 1.0 0.45 0.01 0.15 Max. 1.5 2.508 2.520 2.550 17 -2.7 -2.0 4 1.2 1.0 1.0 0.5 Unit V V V V mV mV/ V A A mA A
1. The deviation parameters VREF(DEV) and IREF(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, VREF, is defined as: { V REF ( DEV ) /V REF ( T A = 25C ) } x 10 V REF ( ppm/C ) = ---------------------------------------------------------------------------------------------------T A where TA is the rated operating free-air temperature range of the device. 2. The dynamic impedance is defined as |ZOUT| = VCOMP/ILED. 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 x 1 + ------I R2
6
(c) 2003 Fairchild Semiconductor Corporation
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OPTICALLY ISOLATED ERROR AMPLIFIER FOD2742A FOD2742B FOD2742C
OUTPUT CHARACTERISTICS (TA = 25C Unless otherwise specified.)
Parameter Collector dark current Emitter-collector voltage breakdown Collector-emitter voltage breakdown Test Conditions (VCE = 10 V) (Fig. 5) (IE = 100 A) (IC = 1.0mA) Symbol ICEO BVECO BVCEO 7 70 Min Typ 1 10 120 Max 50 Unit nA V V
TRANSFER CHARACTERISTICS (TA = 25C Unless otherwise specified.)
Parameter Current transfer ratio Collector-emitter saturation voltage Test Conditions (ILED = 10 mA, VCOMP = VFB, VCE = 5 V) (Fig. 6) Symbol CTR Min 100 Typ 140 0.16 Max 200 0.4 Unit % V
(ILED = 10 mA, VCOMP = VFB, VCE (SAT) IC = 2.5 mA) (Fig. 6)
ISOLATION CHARACTERISTICS (TA = 25C Unless otherwise specified.)
Parameter Input-output insulation leakage current Withstand insulation voltage Resistance (input to output) Test Conditions (RH = 45%, TA = 25C, t = 5s, VI-O = 3000 VDC) (note. 1) (RH <= 50%, TA = 25C, t = 1 min) (note 1) VI-O = 500 VDC (note 1) Symbol II-O VISO RI-O 2500 1012 Min Typ Max 1.0 Unit A Vrms Ohm
SWITCHING CHARACTERISTICS (TA = 25C Unless otherwise specified.)
Parameter Bandwidth Common mode transient immunity at output high Common mode transient immunity at output low Test Conditions (Fig. 7) (ILED = 0 mA, Vcm = 10 VPP RL = 2.2 kV (Fig. 8) (note 2) (ILED = 10 mA, Vcm = 10 VPP RL = 2.2 kV (Fig. 8) (note 2) Symbol BW CMH CML Min Typ 50 1.0 1.0 Max Unit kHZ kV/s kV/s
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.
(c) 2003 Fairchild Semiconductor Corporation
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OPTICALLY ISOLATED ERROR AMPLIFIER FOD2742A FOD2742B
I(LED) I(LED) 8 VF 6 V 7 VREF 5 3 V R1 6 7 VCOMP R2 VREF 5 3 2 8 2
FOD2742C
FIG. 1. VREF, VF, ILED (min) TEST CIRCUIT
FIG. 2. VREF/VCOMP TEST CIRCUIT
I(LED) 8 2
I(OFF) 8 2
IREF 6 V R1 5 5 7 3 V 6 V(LED) 7 3
FIG. 3. IREF TEST CIRCUIT
FIG. 4. I(OFF) TEST CIRCUIT
8
ICEO 2 VCE
I(LED) 8 2 VCE 6 V 7 VCOMP VREF 3
I(C)
6 7
3
5
5
FIG. 5. ICEO TEST CIRCUIT
FIG. 6. CTR, VCE(sat) TEST CIRCUIT
(c) 2003 Fairchild Semiconductor Corporation
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OPTICALLY ISOLATED ERROR AMPLIFIER FOD2742A FOD2742B FOD2742C
VCC = +5V DC IF = 10 mA RL 47
1
8
1f
VOUT
2
7
0.1 VPP
VIN 0.47V
3
6
4
5
Fig. 7 Frequency Response Test Circuit
VCC = +5V DC IF = 0 mA (A) IF = 10 mA (B) R1 2.2k VOUT
1
8
2
7
AB
3
6
4
5
_
VCM
+
10VP-P
Fig. 8 CMH and CML Test Circuit
(c) 2003 Fairchild Semiconductor Corporation
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OPTICALLY ISOLATED ERROR AMPLIFIER FOD2742A
TYPICAL PERFORMANCE CURVES
Fig. 9a - LED Current vs. Cathode Voltage
15 TA = 25C VCOMP = VFB ILED - Supply Current (mA) 1.0
FOD2742B
FOD2742C
Fig. 9b - LED Current vs. Cathode Voltage
TA = 25C VCOMP = VFB
10 ILED - Supply Current (mA) 0.5
5
0
0.0
-5
-0.5
-10
-15 -1 0 1 VCOMP - Cathode Voltage (V) 2 3
-1.0
-1
0
1 VCOMP - Cathode Voltage (V)
2
3
Fig. 10 - Reference Voltage vs. Ambient Temperature
2.510 2.508 VREF - Reference Voltage (V) 2.506 2.504 2.502 2.500 2.498 2.496 2.494 2.492 2.490 -40 -20 0 20 40 60 80 100 ILED = 10mA IREF - Reference Current (A)
Fig. 11 - Reference Current vs Ambient Temperature
ILED = 10mA R1 = 10k 3
2
-40
-20
0
20
40
60
80
100
TA - Ambient Temperature (C)
TA - Ambient Temperature (C)
Fig. 12 - Off-State Current vs. Ambient Temperature
20 VLED = 37V 100 IOFF - Off-state Current (nA) IF - Forward Current (mA) 15
Fig. 13 - Forward Current vs. Forward Voltage
10 70C
25C 0C
10
5
1 -40
-20
0
20
40
60
80
100
0.9
1.0
1.1
1.2
1.3
1.4
TA - Ambient Temperature (C)
VF - Forward Voltage (V)
(c) 2003 Fairchild Semiconductor Corporation
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OPTICALLY ISOLATED ERROR AMPLIFIER FOD2742A
TYPICAL PERFORMANCE CURVES
Fig. 14 - Dark Current vs. Ambient Temperature
30 1000 VCE = 10V 25 100 IC - Collector Current (mA) ILED = 20mA 20 ICEO - Dark Current (nA) VCE = 5V
FOD2742B
FOD2742C
Fig. 15 - Collector Current vs. Ambient Temperature
15
ILED = 10mA
10
10 ILED = 5mA 5 ILED = 1mA
1
0.1 -40
0 -20 0 20 40 60 80 100 0 10 20 30 40 50 60 70 80 90 100 TA - Ambient Temperature (C) TA - Ambient Temperature (C)
Fig. 16 - Current Transfer Ratio vs. LED Current
160 VCE = 5V (IC/IF) - Current Transfer Ratio (%) VCE(sat) - Saturation Voltage (V) 140 0C 25C 120 70C 100 0.24 0.22 0.20 0.18 0.16 0.14 0.12 0.26
Fig. 17 - Saturation Voltage vs. Ambient Temperature
ILED = 10mA IC = 2.5mA
80
60
40 1 10 ILED - Forward Current (mA) 100
0.10 -40
-20
0
20
40
60
80
100
TA - Ambient Temperature (C)
Fig. 18 - Collector Current vs. Collector Voltage
35 TA = 25C 30 IC - Collector Current (mA) 25 20 ILED = 10mA 15 10 5 ILED = 1mA 0 0 1 2 3 4 5 6 7 VCE - Collector-Emitter Voltage (V) 8 9 10 -0.42 Delta Vref / Delta Vout ( mV/V) ILED = 20mA -0.22 -0.24 -0.26 -0.28 -0.30 -0.32 -0.34 -0.36 -0.38 -0.40
Fig. 19 - Rate of Change Vref to Vout vs. Temperature
ILED = 5mA
-0.44 -40
-20
0
20
40
60
80
100
Temperature - C
(c) 2003 Fairchild Semiconductor Corporation
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OPTICALLY ISOLATED ERROR AMPLIFIER FOD2742A
TYPICAL PERFORMANCE CURVES
Fig. 20 - Voltage Gain vs. Frequency
5 VCC=10V IF=10mA
FOD2742B
FOD2742C
0 Voltage Gain - dB RL = 100
-5 RL = 1k -10
RL = 500
-15 1 10 100 Frequency - kHz 1000
(c) 2003 Fairchild Semiconductor Corporation
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OPTICALLY ISOLATED ERROR AMPLIFIER FOD2742A
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.
FOD2742B
Compensation
FOD2742C
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.
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 0.1F 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) /10K = 800A. 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 800A. The collector resistor must thus be such that: 10V - 5V ----------------------------------- < 800A or R COLLECTOR > 6.25K; R COLLECTOR select 12K to allow some margin.
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 V OUT ------------------------- = -------------- - 1 R BOTTOM V REF The absolute value of the top resistor is set by the input offset current of 5.2A. To achieve 0.5% accuracy, the resistance of RTOP should be: V OUT - 2.5 ---------------------------- > 1040A R TOP
(c) 2003 Fairchild Semiconductor Corporation
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OPTICALLY ISOLATED ERROR AMPLIFIER FOD2742A
Package Dimensions
FOD2742B
FOD2742C
Footprint Drawing
0.164 (4.16) 0.144 (3.66)
0.024 (0.61)
1 0.202 (5.13) 0.182 (4.63)
SEATING PLANE
0.060 (1.52) 0.275 (6.99) 0.155 (3.94)
0.143 (3.63) 0.123 (3.13) 0.010 (0.25) 0.006 (0.16)
0.021 (0.53) 0.011 (0.28)
0.008 (0.20) 0.003 (0.08) 0.050 (1.27) TYP
0.244 (6.19) 0.224 (5.69)
0.050 (1.27)
Lead Coplanarity : 0.004 (0.10) MAX
ORDERING INFORMATION
Option R1 R1V R2 R2V Order Entry Identifier R1 R1V R2 R2V Tape and reel (500 units per reel) VDE0884, Tape and reel (500 units per reel) Tape and reel (2,500 units per reel) VDE0884, Tape and reel (2,500 units per reel) Description
MARKING INFORMATION
Definitions
1
2742A V
3 4
2 6
1 2 3 4
Fairchild logo Device number VDE mark (Note: Only appears on parts ordered with VDE option - See order entry table) One digit year code Two digit work week ranging from `01' to `53' Assembly package code
X YY S
5
5 6
(c) 2003 Fairchild Semiconductor Corporation
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OPTICALLY ISOLATED ERROR AMPLIFIER FOD2742A
Carrier Tape Specifications
FOD2742B
FOD2742C
8.0 0.10 3.50 0.20 0.30 MAX 4.0 0.10 2.0 0.05 O1.5 MIN 1.75 0.10
5.5 0.05 8.3 0.10 12.0 0.3 5.20 0.20
0.1 MAX
6.40 0.20
O1.5 0.1/-0
User Direction of Feed
Reflow Profile
300 Temperature (C) 250 200 150 100 50 0 0 0.5 1 1.5 2 2.5 245C peak
230C, 10-30 s
Time above 183C, 120-180 sec Ramp up = 2-10C/sec * Peak reflow temperature: 245C (package surface temperature) * Time of temperature higher than 183C for 120-180 seconds * One time soldering reflow is recommended 3.5 4 4.5
3
Time (Minute)
(c) 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.
(c) 2003 Fairchild Semiconductor Corporation
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