EL20X/EL21X Series 8-Pin SOP Phototransistor Optocoupler Datasheet - SO-8 Package - 3750Vrms Isolation Voltage - Technical Documentation

1. Product Overview

EL20X ve EL21X serileri, fototransistör tabanlı optokuplör (optik kuplaj) ürün ailesidir ve standart 8-pinli Küçük Yüzey Montaj Paketi (SOP) kullanır. Bu cihazlar, kızılötesi ışık yayan diyot (LED) kullanarak sinyalleri bir fototransistör dedektörüne iletir ve böylece iki devre arasında elektriksel izolasyon sağlar. Ana işlevi, herhangi bir doğrudan elektriksel bağlantı olmadan, izolasyon bariyeri üzerinden elektrik sinyallerini iletmek ve böylece yüksek voltajın veya gürültünün bir devreden diğerine yayılmasını önlemektir.

The core advantage of this series lies in its combination of a compact, industry-standard SO-8 package size with robust isolation performance. Key features include a high isolation voltage of up to 3750 V_rms, a wide operating temperature range from -55°C to +110°C, and a high collector-emitter breakdown voltage (BV_CEO). The device offers multiple Current Transfer Ratio (CTR) grades, enabling designers to select an optimized model based on the gain requirements of their specific application. Compliance with environmental and safety standards, such as halogen-free, lead-free, RoHS compliance, and UL/cUL certification, makes it suitable for a wide range of commercial and industrial applications.

1.1 Target Applications

These optocouplers are designed for general-purpose isolation and switching tasks in electronic systems. Typical application areas include:

• Feedback control circuits:Isolating feedback signals in switched-mode power supplies (SMPS) to maintain voltage regulation and protect the control IC.
• System Interface:Coupling digital or analog signals between circuits at different ground potentials or voltage levels, for example, in the interface between a microcontroller and a motor driver or industrial I/O modules.
• General-Purpose Switch:Replace mechanical relays to achieve noiseless solid-state signal switching.
• Monitoring and Detection Circuit:For applications where isolation is critical, such as safety monitoring, fault detection, or line detection.

2. In-depth Technical Parameter Analysis

This section provides a detailed and objective interpretation of the key electrical and optical parameters specified in the datasheet.

2.1 Absolute Maximum Ratings

These ratings define the stress limits that may cause permanent damage to the device. Operation under these conditions is not guaranteed.

• Input Forward Current (I_F):60 mA (continuous). For very short pulses (10 µs), Peak Forward Current (I_FM) is 1 A, which is related to the surge condition during the turn-on period.
• Input reverse voltage (V_R):6 V. The reverse breakdown voltage of the input LED is relatively low; care must be taken in circuit design to avoid applying reverse bias.
• Output collector-emitter voltage (V_CEO):80 V. This is the maximum voltage that can be withstood between the collector and emitter of the phototransistor when the base is open (no light input).
• Total power dissipation (P_TOT):240 mW. This is the maximum total power that the input LED and output transistor can dissipate. The individual limits for input (P_D) and output (P_C) are 90 mW and 150 mW, respectively.
• Isolation voltage (V_ISO):3750 V_rms, for 1 minute. This is a critical safety parameter, tested by applying this AC voltage between all shorted input pins (1-4) and all shorted output pins (5-8). It verifies the dielectric strength of the internal insulation.
• Operating and Storage Temperature:-55°C to +110°C (operating), -55°C to +125°C (storage). The wide range ensures reliability in harsh environments.

2.2 Electro-Optical Characteristics

These parameters are measured under standard test conditions (unless specified, Ta=25°C), defining the performance of the device.

2.2.1 Input (LED) Characteristics

• Forward Voltage (V_F):Typical value 1.3V, maximum 1.5V at I_F= 10 mA. This is used to calculate the current-limiting resistor required for the LED drive circuit.
• Reverse current (I_R):Maximum 100 µA at V_R= 6V, indicating the leakage current of the LED in the off state.

2.2.2 Output (Phototransistor) Characteristics

• Collector-Emitter Dark Current (I_CEO):Maximum 100 µA at V_CE= 10V, I_F= 0mA, maximum 50 nA. This is the leakage current of the phototransistor when there is no light irradiation, which is important for determining the signal level of the "off" state.
• Collector-emitter saturation voltage (V_CE(sat)):In I_F= 10mA, I_C= 2mA, the maximum is 0.4V. When the device is used as a switch, the low saturation voltage helps minimize voltage drop and power loss.

2.2.3 Transfer Characteristics

The most critical parameter of an optocoupler is the Current Transfer Ratio (CTR).

• Definition:CTR = (I_C/ I_F) * 100%, where I_Cis the collector current of the phototransistor, I_Fis the forward current of the LED. It represents the efficiency of converting input current to output current.
• Grading System:This series is divided into specific CTR grades to ensure design consistency.
  • EL20X series (standard CTR at I_F=10mA):EL205 (40-80%), EL206 (63-125%), EL207 (100-200%), EL208 (160-320%).
  • EL21X series (at I_F=10mA minimum CTR):EL211（>20%）、EL212（>50%）、EL213（>100%）。
  • Low current CTR (at I_F=1mA):Different models (EL215, EL216, EL217) are specified for operation at lower LED currents, indicating that CTR depends on I_F.
• Switching speed:Under specified test conditions (V_{=10V, I}=2mA, R_{=100Ω), typical turn-on time (t}on_r) and turn-off time (t_foff_CC) are each 3.0 µs, rise time (t_C) is 1.6 µs, and the fall time (t_L) is 2.2 µs. These parameters limit the maximum frequency of the signal that can be transmitted.
• Isolation parameters:Isolation resistance (R_IO) Typical value is 10¹¹Ω, input and output capacitance (C_IO) typical value is 0.5 pF. Low capacitance is crucial for maintaining high common-mode transient immunity (CMTI) in noisy environments.

3. Performance Curve Analysis

Although the provided PDF excerpt mentions typical characteristic curves but does not show them, their general purpose and impact on design are explained as follows.

3.1 Current Transfer Ratio (CTR) vs. Forward Current (I_F)

Typical curves show that CTR is not constant. It usually peaks at a specific I_F(typically in the 1-10 mA range for such devices) and decreases at lower and higher currents. Designers must refer to this curve to select the optimal operating point that provides sufficient gain and linearity for their application.

3.2 Relationship between CTR and Temperature

CTR has a negative temperature coefficient; it decreases as the ambient temperature increases. This characteristic is crucial for designs operating across the full temperature range from -55°C to +110°C. The circuit design must ensure proper operation (e.g., sufficient output swing or switching capability) even at the maximum expected temperature, where CTR is at its minimum.

3.3 Relationship between Collector Current and Collector-Emitter Voltage

This set of curves with different I_FB as parameters illustrates the output characteristics of the phototransistor. It demonstrates the saturation region (where V_CEis low and I_CC is primarily determined by I_FControl) and the active/linear region. This is crucial for designing linear isolation amplifiers or ensuring the device is fully saturated when used as a switch.

4. Mechanical and Packaging Information

4.1 Pin Configuration

The pin arrangement of the 8-pin SOP package is as follows:Pin 1:Anode,Pin 2:Cathode,Pins 3, 4, 8:No Connection (NC),Pin 5:Emitter,Pin 6:Collector,Pin 7:Base. The base pin is brought out externally, which provides design flexibility. It can be left floating for maximum sensitivity, connected to the emitter through a resistor to reduce sensitivity and increase switching speed, or used for feedback in specific configurations.

4.2 Package Dimensions and PCB Layout

This device conforms to the standard SO-8 package dimensions. The datasheet contains detailed mechanical drawings with dimensions in millimeters. A recommended surface-mount assembly land pattern is also provided. Adhering to this land pattern is crucial for achieving reliable solder joints and preventing issues such as tombstoning during reflow soldering. The package outline ensures compatibility with automated pick-and-place equipment.

5. Welding and Assembly Guide

The absolute maximum rating for soldering temperature is 260°C for 10 seconds. This is a typical rating for lead-free reflow soldering processes. Standard guidelines from IPC/JEDEC J-STD-020 regarding Moisture Sensitivity Level (MSL) and reflow profiles should be followed. Devices should be stored in their original moisture barrier bag until use. If exposed to ambient humidity exceeding their MSL rating, baking is required prior to soldering to prevent "popcorn" damage during reflow.

6. Packaging and Ordering Information

6.1 Model Naming Rules

The model follows the format below:EL2XX(Y)-V

• XX:Model (05, 06, 07, 08, 11, 12, 13, 15, 16, 17). Define CTR rating.
• Y:Tape and reel packaging option (TA, TB, or blank indicates tube).
• V:Optional suffix, indicating inclusion of VDE safety certification.

6.2 Packaging Options

• Tube packaging:100 pieces per tube. Suitable for prototyping or small-batch manual assembly.
• Tape and reel packaging:2000 per reel. Designed for high-volume automatic assembly lines. The datasheet includes detailed reel specifications (cavity dimensions, tape width, reel diameter).

6.3 Device Identification

The top of the package is marked with "EL" (manufacturer code), part number (e.g., 207), a 1-digit year code (Y), and a 2-digit week code (WW). For VDE-certified versions, an optional "V" may be present. This marking allows for component traceability and verification.

7. Application Design Considerations

7.1 Driving the Input LED

An LED must be driven using a current-limiting resistor. The resistor value is calculated as R_LIMIT= (V_DRIVE- V_F) / I_F. Use the maximum V from the datasheet_F, to ensure the required minimum I can be achieved under all conditions._F. For digital switches, considering the switching speed of the device, ensure the drive circuit can provide the necessary I_F, to achieve the desired output state within the required time.

7.2 Output Circuit Design

The load resistor (R_L) connected between the collector and V_CC) determines the output voltage swing and switching speed. A smaller R_Lprovides faster switching speed (due to a smaller RC time constant), but results in a smaller output voltage swing and higher power consumption. A larger R_Lprovides a larger swing but slower speed. The selected I_Fand CTR must ensure that the phototransistor can sink sufficient current when turned on to pull the output voltage below the logic low threshold of the receiving circuit.

7.3 Using the Base Pin

Leaving the base pin (pin 7) open provides the highest CTR and sensitivity. Connecting a resistor (typically in the range of 100 kΩ to 1 MΩ) between the base and emitter (pin 5) shunts some of the photogenerated base current, reducing the effective gain (CTR) but significantly improving the switching speed, especially the turn-off time (t_off). This is a common trade-off in high-speed digital isolation applications.

7.4 Ensuring Reliable Isolation

To maintain the rated isolation voltage, proper PCB layout is crucial. According to relevant safety standards (e.g., IEC 60950, IEC 60601), maintain sufficient creepage and clearance distances between the copper traces on the input and output sides on the PCB. The isolation barrier inside the component is certified, but the PCB layout must not compromise it.

8. Technical Comparison and Selection Guidance

The EL20X/EL21X series stands out with its isolation voltage of up to 3750V in the standard SO-8 package,_rmswhich is higher than many basic 4-pin optocouplers. Compared to more advanced digital isolators (using CMOS technology), such phototransistor optocouplers are typically slower, have lower CTR, and CTR degrades over time. However, they offer excellent common-mode rejection, simplicity, and robustness for DC and low-frequency AC signal isolation. Key selection criteria are: required isolation voltage, necessary CTR at operating I_F, acceptable switching speed, and operating temperature range.

9. Frequently Asked Questions (FAQ)

9.1 What are the differences between the EL20X and EL21X series?

The EL20X series (EL205-EL208) specifies both minimum and maximum CTR values (a "graded" range), providing tighter parameter control. The EL21X series (EL211-EL213) specifies only a minimum CTR value, which may result in a wider distribution of actual values but potentially at a lower cost.

9.2 How does temperature affect performance?

CTR decreases as temperature increases. For reliable operation across the entire temperature range, design calculations should use the minimum expected CTR at the maximum operating temperature. Datasheets typically provide derating curves or temperature coefficients for this purpose.

9.3 Shin wannan na'urar za a iya amfani da ita don keɓe siginar analog?

Yes, but with limitations. The response of the phototransistor is nonlinear, and the CTR varies with I_Fand temperature. For linear analog isolation, additional external circuitry (op-amp, feedback) is required to linearize the response, or dedicated linear optocouplers should be considered.

What is the purpose of the "V" option in the 9.4 model?

The "-V" suffix indicates that the specific unit has been tested and certified to comply with the VDE (Verband der Elektrotechnik, Elektronik und Informationstechnik) safety standard for reinforced insulation. This is typically a requirement for products sold in the European market.

10. Practical Design Examples

Scene:Isolate a 3.3V microcontroller GPIO pin to control a 12V relay coil on another circuit. The relay coil requires 50mA to energize.

Design Steps:

1. Interface Selection:Using an optocoupler as a low-side switch for the relay. The microcontroller drives the LED side. The phototransistor will sink the relay coil current.
2. Device Selection:Select a model with sufficient CTR. Required I_C= 50mA. If the goal is to supply I_F= 5mA from an MCU, then the required minimum CTR = (50mA / 5mA)*100% = 1000%. A standard phototransistor cannot provide this value. Therefore, the photocoupler must drive a small transistor ("post-transistor"), which then drives the relay. Select EL207 (CTR 100-200%) for good gain.
3. Input circuit:MCU GPIO（3.3V）-> 限流电阻R1 -> EL207引脚1（阳极）和2（阴极）。R1 = (3.3V - 1.5V) / 0.005A = 360Ω（使用330Ω标准值）。
4. Output circuit:12V电源 -> 继电器线圈 -> EL207的集电极（引脚6）。发射极（引脚5）接地。必须在继电器线圈两端反向并联一个续流二极管，以保护光敏三极管在关断时免受电压尖峰的影响。可以在引脚7添加一个基极-发射极电阻（例如1 MΩ）以改善关断速度。
5. Verification:In I_FAt =5mA, a minimum CTR of 100% can provide I_C= 5mA. This is sufficient to saturate a small BJT with high gain (e.g., 2N3904), which can then switch a 50mA relay coil.

11. Working Principles

Photocoupler terdiri dari dua komponen utama yang dikemas dalam satu paket kedap cahaya. Di sisi input, sebuah dioda pemancar cahaya (LED) inframerah gallium arsenida (GaAs) mengubah arus listrik menjadi cahaya inframerah. Intensitas cahaya ini sebanding dengan arus maju (I_F) yang mengalir melalui LED. Cahaya ini melintasi celah isolasi transparan (biasanya diisi dengan gel dielektrik) dan menyinari fototransistor silikon di sisi output. Daerah basis fototransistor dirancang sensitif terhadap panjang gelombang cahaya spesifik ini. Foton yang datang menghasilkan pasangan elektron-lubang di persimpangan basis-kolektor, membentuk arus foto yang berfungsi sebagai arus basis. Kemudian, arus basis fotogenerasi ini diperkuat oleh penguatan arus transistor (h_FE), menghasilkan arus kolektor (I yang lebih besar._C). Ratio I_C/I_Fis the Current Transfer Ratio (CTR). The key point is that the signal is transmitted via light, providing electrical isolation determined by the physical properties of the internal insulating material and the distance between the LED and the transistor.

12. Technical Trends

Photocouplers based on phototransistors, such as the EL20X/EL21X series, represent a mature and reliable isolation technology. The current trend in signal isolation includes the increasing adoption of digital isolators based on CMOS technology and those utilizing RF or capacitive coupling.Digital isolator。这些在速度（高达数百Mbps）、功耗、尺寸和寿命（无LED退化）方面具有显著优势。然而，传统光电耦合器在需要极高隔离电压（>5kV）、优异的共模瞬态抗扰度（CMTI）、简单性以及直流和低频隔离的成本效益的应用中仍保持强势地位。光电耦合器技术本身也在不断发展，例如将光敏三极管与基极-发射极电阻集成以提高速度（如基极引脚的可用性所示），以及开发具有更高爬电距离/电气间隙的封装以满足加强绝缘要求。