HCNR200 HCNR201数据手册

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HCNR200 and HCNR201

High-Linearity Analog Optocouplers

Data Sheet

Lead (Pb) FreeRoHS 6 fullycompliant

y compliant options available;-xxxE denotes a lead-free product

Description

The HCNR200/201 high-linearity analog optocoupler consists of a high-performance AlGaAs LED that illumi-nates two closely matched photodiodes. The input pho-todiode can be used to monitor, and therefore stabilize, the light output of the LED. As a result, the non-linearity and drift characteristics of the LED can be virtually elimi-nated. The output photodiode produces a photocur rent that is linearly related to the light output of the LED. The close matching of the photo-diodes and advanced de-sign of the package ensure the high linearity and stable gain characteristics of the opto coupler. The HCNR200/201 can be used to isolate analog signals in a wide variety of applications that require good stabil-ity, linearity, bandwidth and low cost. The HCNR200/201 is very fl exible and, by appro priate design of the appli-cation circuit, is capable of operating in many diff erent modes, includ ing: unipolar/bipolar, ac/dc and inverting/non-inverting. The HCNR200/201 is an excellent solution for many analog isola tion problems.

Features

Low nonlinearity: 0.01%

K3 (IPD2/IPD1) transfer gain HCNR200: ±15% HCNR201: ±5%

Low gain temperature coeffi cient: -65 ppm/°C Wide bandwidth – DC to >1 MHz Worldwide safety approval

– UL 1577 recognized (5 kV rms/1 min rating)– CSA approved

– IEC/EN/DIN EN 60747-5-2 approved VIORM = 1414 V peak (option #050)

Surface mount option available (Option #300) 8-Pin DIP package - 0.400” spacing Allows fl exible circuit design

Applications

Low cost analog isolation Telecom: Modem, PBX Industrial process control:Transducer isolator Isolator for thermo couples 4 mA to 20 mA loop isola-tion

SMPS feedback loop, SMPS feedforward Monitor motor supply voltage Medical

Schematic

LED CATHODE

LED ANODE

F

NCNC

PD1 CATHODE

I

IPD2 CATHODE

PD1 ANODE

PD2 ANODE

CAUTION: It is advised that normal static precautions be taken in handling and assemblyof this component to prevent damage and/

or degradation which may be induced by ESD.

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Ordering Information

HCNR200/HCNR201 is UL Recognized with 5000 Vrms for 1 minute per UL1577.

To order, choose a part number from the part number column and combine with the desired option from the option column to form an order entry.

Example 1: HCNR200-550E to order product of Gull Wing Surface Mount package in Tape and Reel packaging with IEC/EN/DIN EN 60747-5-2 VIORM = 1414 Vpeak Safety Approval and UL 5000 Vrms for 1 minute rating and RoHS compliant.

Example 2: HCNR201 to order product of 8-Pin Widebody DIP package in Tube packaging with UL 5000 Vrms for 1 minute rating and non RoHS compliant.

Option datasheets are available. Contact your Avago sales representative or authorized distributor for information.Remarks: The notation ‘#XXX’ is used for existing products, while (new) products launched since July 15, 2001 and RoHS compliant will use ‘–XXXE.’

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Package Outline Drawings

0.20 (0.008)MARKING

MAX.

1.80 (0.071)

XXX = 050 ONLY if option #050,#350,#550 (or -050,-350,-550) ordered (otherwise blank)yy - Year

ww - Work Week

Marked with black dot - Designates Lead Free option E* - Designates pin 1

NOTE: FLOATING LEAD PROTRUSION IS 0.25 mm (10 mils) MAX.

Figure 1a. 8 PIN DIP

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Gull Wing Surface Mount Option #300

MAX.1.78 ± 0.15BSC

DIMENSIONS IN MILLIMETERS (INCHES).

LEAD COPLANARITY = 0.10 mm (0.004 INCHES).

NOTE: FLOATING LEAD PROTRUSION IS 0.25 mm (10 mils) MAX.

Figure 1b. 8 PIN Gull Wing Surface Mount Option #300

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Solder Refl ow Temperature Profi le

TEMPERATURE (°C)

ROOMTEMPERATURE

TIME (SECONDS)

NOTE: NON-HALIDE FLUX SHOULD BE USED.

Recommended Pb-Free IR Profi le

TpTL

TEMPERATURE

TsmaxTsmin

25

NOTES:

THE TIME FROM 25 °C to PEAKTEMPERATURE = 8 MINUTES MAX.Tsmax = 200 °C, Tsmin = 150 °C

NOTE: NON-HALIDE FLUX SHOULD BE USED.

TIME

Regulatory Information

The HCNR200/201 optocoupler features a 0.400” wide, eight pin DIP package. This package was specifi cally designed to meet worldwide regulatory require ments. The HCNR200/201 has been approved by the following organizations:UL

IEC/EN/DIN EN 60747-5-2

Approved under

IEC 60747-5-2:1997 + A1:2002EN 60747-5-2:2001 + A1:2002

DIN EN 60747-5-2 (VDE 0884 Teil 2):2003-01(Option 050 only)

Recognized under UL 1577, Component Recognition Program, FILE E55361

CSA

Approved under CSA Component Acceptance Notice #5, File CA 88324

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Insulation and Safety Related Specifi cations Parameter Symbol

Min. External Clearance (External Air Gap) Min. External Creepage (External Tracking Path)

Min. Internal Clearance (Internal Plastic Gap)

L(IO1) L(IO2) CTI

Value

9.6 10.0 1.0 4.0 200 IIIa

Units Conditions

mm mm mm mm V

Measured from input terminals to outputterminals, shortest distance through airMeasured from input terminals to outputterminals, shortest distance path along bodyThrough insulation distance conductor toconductor, usually the direct distance

between the photoemitter and photodetectorinside the optocoupler cavity

The shortest distance around the borderbetween two diff erent insulating materialsmeasured between the emitter and detectorDIN IEC 112/VDE 0303 PART 1Material group (DIN VDE 0110)

Min. Internal Creepage (Internal Tracking Path)

Comparative Tracking Index Isolation Group

Option 300 – surface mount classifi cation is Class A in accordance with CECC 00802.

IEC/EN/DIN EN 60747-5-2 Insulation Characteristics (Option #050 Only) Description

Installation classifi cation per DIN VDE 0110/1.89, Table 1 For rated mains voltage ≤600 V rms For rated mains voltage ≤1000 V rms Climatic Classifi cation (DIN IEC 68 part 1)

Pollution Degree (DIN VDE 0110 Part 1/1.89) Maximum Working Insulation Voltage

Symbol

Characteristic

I-IVI-III55/100/21

2

Unit

VIORMV peakVPRV peak

Input to Output Test Voltage, Method b*

VPR = 1.875 x VIORM, 100% Production Test with tm = 1 sec, Partial Discharge < 5 pC

Input to Output Test Voltage, Method a*

VPR = 1.5 x VIORM, Type and sample test, tm = 60 sec, Partial Discharge < 5 pC

Highest Allowable Overvoltage*

(Transient Overvoltage, tini = 10 sec)

V VPRpeak

VIOTMV peak

Safety-Limiting Values

(Maximum values allowed in the event of a failure, also see Figure 11) Case Temperature

Current (Input Current IF, PS = 0) Output Power

Insulation Resistance at TS, VIO = 500 V

TS°C

ISmAPS,OUTPUTmWRS9

Ω

*Refer to the front of the Optocoupler section of the current catalog for a more detailed description of IEC/EN/DIN EN 60747-5-2 and other prod-uct safety regulations.

Note: Optocouplers providing safe electrical separation per IEC/EN/DIN EN 60747-5-2 do so only within the safety-limiting values to which they

are qualifi ed. Protective cut-out switches must be used to ensure that the safety limits are not exceeded.

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Absolute Maximum Ratings

Storage Temperature ..............................................................................................-55°C to +125°COperating Temperature (TA) .................................................................................-55°C to +100°CJunction Temperature (TJ) .........................................................................................................125°CRefl ow Temperature Profi le ..............................................See Package Outline Drawings SectionLead Solder Temperature ............................................................................................260°C for 10s (up to seating plane)

Average Input Current - IF ........................................................................................................25 mAPeak Input Current - IF ...............................................................................................................40 mA (50 ns maximum pulse width)Reverse Input Voltage - VR ............................................................................................................2.5 V (IR = 100 μA, Pin 1-2)Input Power Dissipation ....................................................................................60 mW @ TA = 85°C (Derate at 2.2 mW/°C for operating temperatures above 85°C)

Reverse Output Photodiode Voltage ........................................................................................30 V (Pin 6-5)

Reverse Input Photodiode Voltage ............................................................................................30 V (Pin 3-4)

Recommended Operating Conditions

Storage Temperature .................................................................................................-40°C to +85°COperating Temperature ............................................................................................-40°C to +85°CAverage Input Current - IF ..................................................................................................1 - 20 mAPeak Input Current - IF ...............................................................................................................35 mA (50% duty cycle, 1 ms pulse width)

Reverse Output Photodiode Voltage ..................................................................................0 - 15 V (Pin 6-5)

Reverse Input Photodiode Voltage ......................................................................................0 - 15 V (Pin 3-4)

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Electrical Specifi cations

T

= 25°C unless otherwise specifi ed.

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AC Electrical Specifi cations

TA = 25°C unless otherwise specifi ed.

Parameter

LED Bandwidth

Application Circuit Bandwidth: High Speed High Precision Application Circuit: IMRR High Speed

Symbol

f -3dB

Device

Min.

Typ.

9 10 95

Max.

Units

MHz

Test Conditions

IF = 10 mA

Fig. Note

MHz kHz dB

freq = 60 Hz

16

666, 7

Package Characteristics

T

= 25°C unless otherwise specifi ed.*The Input-Output Momentary Withstand Voltage is a dielectric voltage rating that should not be interpreted as an input-output continuous voltage rating. For the continuous voltage rating refer to the VDE 0884 Insulation Characteristics Table (if applicable), your equipment level safety specifi cation, or Application Note 1074, “Optocoupler Input-Output Endurance Voltage.”

Notes:

1. K3 is calculated from the slope of the best fi t line of IPD2 vs. IPD1 with eleven equally distributed data points from 5 nA to 50 μA. This is approxi-mately equal to IPD2/IPD1 at IF = 10 mA.

2. BEST FIT DC NONLINEARITY (NLBF) is the maximum deviation expressed as a percentage of the full scale output of a “best fi t” straight line from a graph of IPD2 vs. IPD1 with eleven equally distrib uted data points from 5 nA to 50 μA. IPD2 error to best fi t line is the deviation below and above the best fi t line, expressed as a percentage of the full scale output.

3. ENDS FIT DC NONLINEARITY (NLEF) is the maximum deviation expressed as a percentage of full scale output of a straight line from the 5 nA to the 50 μA data point on the graph of IPD2 vs. IPD1.

4. Device considered a two-terminal device: Pins 1, 2, 3, and 4 shorted together and pins 5, 6, 7, and 8 shorted together.

5. In accordance with UL 1577, each optocoupler is proof tested by applying an insulation test voltage of ≥6000 V rms for ≥1 second (leakage detection current limit, II-O of 5 μA max.). This test is performed before the 100% production test for partial discharge (method b) shown in the IEC/EN/DIN EN 60747-5-2 Insulation Characteris-tics Table (for Option #050 only).6. Specifi c performance will depend on circuit topology and components.7. IMRR is defi ned as the ratio of the signal gain (with signal applied to VIN of Figure 16) to the isolation mode gain (with VIN connected to input common and the signal applied between the input and output commons) at 60 Hz, expressed in dB.

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N

IAG REFSNART – 3K DEZILAMRON

IPD1 – INPUT PHOTODIODE CURRENT – µAFigure 2. Normalized K3 vs. input IPD.

%

– YTIRAENIL-NON TIF-TSEB – FBLNTA – TEMPERATURE – °CFigure 5. NLBF vs. temperature.A

n – EGAKAEL EDOIDOTOHP – KLI-55

-255356595125

TA – TEMPERATURE – °CFigure 8. Typical photodiode leakage vs. temperature.

N

IAG REFSNART 3K FO TFIRD – 3K ATLEDTA – TEMPERATURE – °CFigure 3. K3 drift vs. temperature.

S

TP % – LN TIF-TSEB FO TFIRD – FBLN ATLEDTA – TEMPERATURE – °CFigure 6. NLBF drift vs. temperature.

100

TA = 25°C

A

10

m – TNE1RRUC D0.1RAWR0.01

OF – FI0.0010.0001

1.20

1.301.401.501.60VF – FORWARD VOLTAGE – VOLTSFigure 9. LED input current vs. forward voltage.)

SF FO %( ENIL TIF-TSEB MORF RORRE 2D

PIIPD1 – INPUT PHOTODIODE CURRENT – µA

Figure 4. IPD2 error vs. input IPD (see note 4).

R

TC EDOIDOTOHP TUPNI – 1K DEZILAMRONIF – LED INPUT CURRENT – mA

Figure 7. Input photodiode CTR vs. LED input current.

V

– EGATL

OV DRAWROF DEL – FVTA – TEMPERATURE – °C

Figure 10. LED forward voltage vs. temperature.

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TS – CASE TEMPERATURE – °C

Figure 11. Thermal derating curve dependence of safety limiting value with case temperature per IEC/EN/DIN EN 60747-5-2.

VII

F

OUT

A) BASIC TOPOLOGY

VPD2

OUT

B) PRACTICAL CIRCUIT

Figure 12. Basic isolation amplifi er.

V

OUT

A) POSITIVE INPUT B) POSITIVE OUTPUT

VOUT

D) NEGATIVE OUTPUT

Figure 13. Unipolar circuit topologies.

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VVV

OUT

A) SINGLE OPTOCOUPLER

VOUT

B) DUAL OPTOCOUPLER

Figure 14. Bipolar circuit topologies.

+IIN

-IIN

A) RECEIVER

V

OUT

OUT

OUT

B) TRANSMITTER

Figure 15. Loop-powered 4-20 mA current loop circuits.

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OUT

VFigure 16. High-speed low-cost analog isolator.

V+15 V

INPUTBNC

OUTPUTBNC

Figure 17. Precision analog isolation amplifi er.

MAG

VIN

VCC1 = +15 VVEE1 = -15 V

Figure 18. Bipolar isolation amplifi er.

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VIN

MAG

SIGN

Figure 19. Magnitude/sign isolation amplifi er.

Figure 20. SPICE model listing.

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+ILOOP

25 Ω

OUT

Design Equations:

VOUT / ILOOP = K3 (R5 R3) / R1 + R3)K3 = K2 / K1 = Constant = 1

Note:

The two OP-AMPS shown are two separate LM158, and not two channels in a single dual package, otherwise the loop side and output side will not be properly isolated.

Figure 21. 4 to 20 mA HCNR200 receiver circuit.

LOOPVin

ILOOP

Design Equations:

(ILOOP/Vin)=K3(R5+R3)/(R5R1)K3 = K2/K1 = Constant ≈ 1

Note:

The two OP-AMPS shown are two separate LM158 IC’s, and NOT dual channels in a single package, otherwise, the LOOP side and input side will not be properly isolated; The 5V1 Zener should be properly selected to ensure that it conducts at 187μA;

Figure 22. 4 to 20 mA HCNR200 transmitter circuit.

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Theory of Operation

Figure 1 illustrates how the HCNR200/201 high-linearity optocouplerisconfi gured. The basic optocoupler con-sists of an LED and two photodiodes. The LED and one of the photodiodes (PD1) is on the input leadframe and the other photodiode (PD2) is on the output leadframe. The package of the optocoupler is constructed so that each photo diode receives approxi mately the same amount of light from the LED.

An external feedback amplifi er can be used with PD1 to monitor the light output of the LED and automatically adjust the LED current to compensate for any non-linear-ities or changes in light output of the LED. The feedback amplifi er acts to stabilize and linearize the light output of the LED. The output photodiode then converts the stable, linear light output of the LED into a current, which can then be converted back into a voltage by another amplifi er.

Figure 12a illustrates the basic circuit topology for implement ing a simple isolation amplifi er using the HCNR200/201 optocoupler. Besides the optocoupler, two external op-amps and two resistors are required.

This simple circuit is actually a bit too simple to function properly in an actual circuit, but it is quite useful for ex-plaining how the basic isolation amplifi er circuit works (a few more components and a circuit change are required

to make a practical circuit, like the one shown in Figure 12b).The operation of the basic circuit may not be immedi-ately obvious just from inspecting Figure 12a, particu-larly the input part of the circuit. Stated briefl y, amplifi er

A1 adjusts the LED current (Iin PD1 (IF

), and therefore the current PD1), to maintain its “+” input terminal at 0 V. For example, increasing the input voltage would tend to in-crease the voltage of the “+” input terminal of A1 above 0 V. A1 amplifi es that increase, causing IF to increase, as well as II will pull the “+” terminal of the op-amp back toward PD1. Because of the way that PD1 is connected, ground. A1 will continue to increase IPD1nal is back at 0 V. Assuming that A1 is a perfect op-amp, F until its “+” termi-no current fl ows into the inputs of A1; therefore, all of the current fl owing through R1 will fl ow through PD1. Since the “+” input of A1 is at 0 V, the current through R1, and thereforeIPD1 as well, is equal to VIN/R1.Essentially, amplifi er A1 adjusts IF so that

IPD1 = VIN/R1.

Notice that Ithe value of R1 and is independent of the light output PD1 depends ONLY on the input voltage and

characteris tics of the LED. As the light output of the LED changes with temperature, ampli fi er A1 adjusts IF to compensate and maintain a constant current in PD1. Also notice that IPD1 is exactly proportional to VIN, giving a very linear relationship between the input voltage and the photodiode current.

The relationship between the input optical power and the output current of a photodiode is very linear. There-fore, by stabiliz ing and linearizing Ithe LED is also stabilized and linearized. And since light PD1, the light output of from the LED falls on both of the photodiodes, IPD2 will be stabilized as well.

The physical construction of the package determines the relative amounts of light that fall on the two photodiodes and, therefore, the ratio of the photodiode currents. This

results in very stable operation over time and tempera-ture. The photodiode current ratio can be expressed as a constant, K, where

K = IPD2/IPD1.Amplifi er A2 and resistor R2 form a trans-resistance am-plifi er that converts IPD2 back into a voltage, VOUT, where

VOUT = IPD2*bining the above three equations yields an overall expression relating the output voltage to the input volt-age,

VOUT/VIN = K*(R2/R1).

Therefore the relationship between VIN and Vstant, linear, and independent of the light output

OUT is con-characteris tics of the LED. The gain of the basic isola tion amplifi er circuit can be adjusted simply by adjusting the ratio of R2 to R1. The parameter K (called K cations) can be thought of as the gain of the 3 in the electri-cal specifioptocoupler and is specifi ed in the data sheet.Remember, the circuit in Figure 12a is simplifi ed in order to explain the basic circuit opera tion. A practical circuit, more like Figure 12b, will require a few additional compo-nents to stabilize the input part of the circuit, to limit the LED current, or to optimize circuit performance. Example applica tion circuits will be discussed later in the data sheet.

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Circuit Design Flexibility

Circuit design with the HCNR200/201 is very fl exible because the LED and both photodiodes are acces sible to the designer. This allows the designer to make perf-ormance trade-off s that would otherwise be diffi cult to make with commercially avail able isolation amplifi ers (e.g., band width vs. accuracy vs. cost). Analog isola tion circuits can be designed for applications that have either unipolar (e.g., 0-10 V) or bipolar (e.g., ±10 V) signals, with positive or negative input or output voltages. Several simplifi ed circuit topologies illustrating the design fl ex-ibility of the HCNR200/201 are discussed below.The circuit in Figure 12a is confi gured to be non-invert-ing with positive input and output voltages. By simply changing the polarity of one or both of the photodiodes, the LED, or the op-amp inputs, it is possible to imple ment other circuit confi gu ra tions as well. Figure 13 illustrates how to change the basic circuit to accommodate both positive and negative input and output voltages. The in-put and output circuits can be matched to achieve any combina tion of positive and negative voltages, allowing for both inverting and non-inverting circuits.

All of the confi gurations described above are unipolar (single polar ity); the circuits cannot accom mo date a sig-nal that might swing both positive and negative. It is pos-sible, however, to use the HCNR200/201 optocoupler to implement a bipolar isolation amplifi er. Two topologies that allow for bipolar operation are shown in Figure 14.The circuit in Figure 14a uses two current sources to off set the signal so that it appears to be unipolar to the optocoupler. Current source IOS1 provides enough off set to ensure that IPD1 is always positive. The second current source, Itain a net circuit offOS2, provides an off set of opposite polarity to ob- set of zero. Current sources IOS1 and Isuitable voltage sources.

OS2 can be implemented simply as resistors connected to The circuit in Figure 14b uses two optocouplers to obtain bipolar operation. The fi rst optocoupler handles the pos-itive voltage excursions, while the second optocoupler handles the negative ones. The output photo diodes are connected in an antiparallel confi guration so that they produce output signals of opposite polarity.

The fi rst circuit has the obvious advantage of requiring only one optocoupler; however, the off set performance of the circuit is dependent on the matching of IIOS1 and OS2 and is also dependent on the gain of the optocoupler. Changes in the gain of the opto coupler will directly af-fect the off set of the circuit.The off set performance of the second circuit, on the other hand, is much more stable; it is inde pendent of optocoupler gain and has no matched current sources

to worry about. How ever, the second circuit requires two optocouplers, separate gain adjustments for the posi-tive and negative portions of the signal, and can exhibit crossover distor tion near zero volts. The correct circuit to choose for an applica tion would depend on the require-ments of that particular application. As with the basic isolation amplifi er circuit in Figure 12a, the circuits in Fig-ure 14 are simplifi ed and would require a few additional compo nents to function properly. Two example circuits that operate with bipolar input signals are discussed in the next section.

As a fi nal example of circuit design fl exibility, the simpli-fi ed schematics in Figure 15 illus trate how to implement 4-20 mA analog current-loop transmitter and receiver circuits using the HCNR200/201 optocoupler. An impor-tant feature of these circuits is that the loop side of the circuit is powered entirely by the loop current, eliminat-ing the need for an isolated power supply.

The input and output circuits in Figure 15a are the same as the negative input and positive output circuits shown in Figures 13c and 13b, except for the addition of R3 and zener diode D1 on the input side of the circuit. D1 regu-lates the supply voltage for the input amplifi er, while R3 forms a current divider with R1 to scale the loop current down from 20 mA to an appropriate level for the input circuit (<50 μA).

As in the simpler circuits, the input amplifi er adjusts the LED current so that both of its input terminals are at the same voltage. The loop current is then divided

between R1 and R3. Iis given by the following equation:PD1 is equal to the current in R1 and

IPD1 = ILOOP*R3/(R1+R3).

Combining the above equation with the equations used for Figure 12a yields an overall expression relating the output voltage to the loop current,

VOUT/ILOOP = K*(R2*R3)/(R1+R3).

Again, you can see that the relationship is constant, lin-ear, and independent of the charac teristics of the LED. The 4-20 mA transmitter circuit in Figure 15b is a little dif-ferent from the previous circuits, partic ularly the output circuit. The output circuit does not directly generate an output voltage which is sensed by R2, it instead uses Q1 to generate an output current which fl ows through R3. This output current generates a voltage across R3, which is then sensed by R2. An analysis similar to the one above yields the following expression relating output current to input voltage:

ILOOP/VIN = K*(R2+R3)/(R1*R3).

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The preceding circuits were pre sented to illustrate the fl exibility in designing analog isolation circuits using the HCNR200/201. The next section presents several com-plete schematics to illustrate practical applications of the HCNR200/201.

Example Application Circuits

The circuit shown in Figure 16 is a high-speed low-cost circuit designed for use in the feedback path of switch-mode power supplies. This application requires good bandwidth, low cost and stable gain, but does not re-quire very high accuracy. This circuit is a good example of how a designer can trade off accuracy to achieve improve ments in bandwidth and cost. The circuit has a bandwidth of about 1.5 MHz with stable gain character-istics and requires few external components.

Although it may not appear so at fi rst glance, the circuit in Figure 16 is essentially the same as the circuit in Fig-ure 12a. Amplifi er A1 is comprised of Q1, Q2, R3 and R4, while amplifi er A2 is comprised of Q3, Q4, R5, R6 and R7. The circuit operates in the same manner as well; the only diff erence is the performance of amplifi ers A1 and A2. The lower gains, higher input currents and higher off set voltages aff ect the accuracy of the circuit, but not the way it operates. Because the basic circuit operation has not changed, the circuit still has good gain stability. The use of discrete transistors instead of op-amps allowed the design to trade off accuracy to achieve good band-width and gain stability at low cost.

To get into a little more detail about the circuit, R1 is se-lected to achieve an LED current of about 7-10 mA at the nominal input operating voltage according to the fol-lowing equation:

IF = (VIN/R1)/K1,

where K1 (i.e., IPD1/IF) of the optocoupler is typically about

0.5%. R2 is then selected to achieve the desired output volt age according to the equation,

VOUT/VIN = R2/R1.

The purpose of R4 and R6 is to improve the dynamic re-sponse (i.e., stability) of the input and output circuits by lowering the local loop gains. R3 and R5 are selected to provide enough current to drive the bases of Q2 and Q4. And R7 is selected so that Q4 operates at about the same collector current as Q2.

The next circuit, shown in Figure 17, is designed to achieve the highest possible accuracy at a reasonable cost. The high accuracy and wide dynamic range of the circuit is achieved by using low-cost precision op-amps with very low input bias currents and off set voltages and is limited by the performance of the opto coupler. The circuit is de-signed to operate with input and output voltages from 1 mV to 10 V.

The circuit operates in the same way as the others. The only major diff erences are the two compensa tion capaci-tors and additional LED drive circuitry. In the high-speed circuit discussed above, the input and output circuits are stabilized by reducing the local loop gains of the input and output circuits. Because reducing the loop gains would decrease the accuracy of the circuit, two compen-sation capacitors, C1 and C2, are instead used to improve circuit stability. These capacitors also limit the bandwidth of the circuit to about 10 kHz and can be used to reduce the output noise of the circuit by reducing its bandwidth even further.

The additional LED drive circuitry (Q1 and R3 through R6) helps to maintain the accuracy and band width of the circuit over the entire range of input voltages. Without these components, the transcon duc t ance of the LED driver would decrease at low input voltages and LED currents. This would reduce the loop gain of the input circuit, reducing circuit accuracy and bandwidth. D1 pre-vents excessive reverse voltage from being applied to the LED when the LED turns off completely.No off set adjustment of the circuit is necessary; the gain can be adjusted to unity by simply adjusting the 50 kohm poten tiometer that is part of R2. Any OP-97 type of op-amp can be used in the circuit, such as the LT1097 from Linear Technology or the AD705 from Analog Devices, both of which off er pA bias currents, μV off set voltages and are low cost. The input terminals of the op-amps and the photodiodes are connected in the circuit using Kelvin connections to help ensure the accuracy of the circuit. The next two circuits illustrate how the HCNR200/201 can be used with bipolar input signals. The isolation amplifi er in Figure 18 is a practical implemen tation of the circuit shown in Figure 14b. It uses two opto couplers, OC1 and OC2; OC1 handles the positive portions of the input sig-nal and OC2 handles the negative portions.

Diodes D1 and D2 help reduce crossover distortion by keeping both amplifi ers active during both positive and negative portions of the input signal. For example, when the input signal positive, optocoupler OC1 is active while OC2 is turned off . However, the amplifi er control ling OC2 is kept active by D2, allowing it to turn on OC2 more rap-idly when the input signal goes negative, thereby reduc-ing crossover distortion.

Balance control R1 adjusts the relative gain for the posi-tive and negative portions of the input signal, gain con-trol R7 adjusts the overall gain of the isolation amplifi er, and capac i tors C1-C3 provide compensa tion to stabilize the amplifi ers.

模拟光耦

The fi nal circuit shown in Figure 19 isolates a bipolar analog signal using only one optocoupler and generates two output signals: an analog signal proportional to the magnitude of the input signal and a digital signal cor-responding to the sign of the input signal. This circuit is especially useful for applica tions where the output of HCNR200/201 SPICE Model

Figure 20 is the net list of a SPICE macro-model for the HCNR200/201 high-linearity optocoupler. The macro-model accurately refl ects the primary characteristics of the HCNR200/201 and should facilitate the design and understanding of circuits using the HCNR200/201 opto-the circuit is going to be applied to an analog-to-digital converter. The primary advantages of this circuit are very coupler.

good linearity and off set, with only a single gain adjust-ment and no off set or balance adjustments.To achieve very high linearity for bipolar signals, the gain should be exactly the same for both positive and negative input polarities. This circuit achieves excellent linearity by using a single optocoupler and a single input resistor, which guarantees identical gain for both posi-tive and negative polarities of the input signal. This pre-cise matching of gain for both polari ties is much more diffi cult to obtain when separate components are used for the diff erent input polari ties, such as is the pre vious circuit.

The circuit in Figure 19 is actually very similar to the pre-vious circuit. As mentioned above, only one optocoupler is used. Because a photodiode can conduct current in only one direction, two diodes (D1 and D2) are used to steer the input current to the appropriate terminal of input photodiode PD1 to allow bipolar input currents. Normally the forward voltage drops of the diodes would cause a serious linearity or accuracy problem. However, an additional amplifi er is used to provide an appropriate off set voltage to the other amplifi ers that exactly cancels the diode voltage drops to maintain circuit accuracy.Diodes D3 and D4 perform two diff erent functions; the diodes keep their respective amplifi ers active indepen-dent of the input signal polarity (as in the previous cir-cuit), and they also provide the feedback signal to PD1 that cancels the voltage drops of diodes D1 and D2.Either a comparator or an extra op-amp can be used to sense the polarity of the input signal and drive an inex-pensive digital optocoupler, like a 6N139.

It is also possible to convert this circuit into a fully bipolar circuit (with a bipolar output signal) by using the output of the 6N139 to drive some CMOS switches to switch the polarity of PD2 depending on the polarity of the input signal, obtaining a bipolar output voltage swing.

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