ELD3H7 ELQ3H7 Photocoupler Datasheet - 8-Pin/16-Pin SSOP Package - Isolation Voltage 3750Vrms - CTR 50-600% - English Technical Document

1. Product Overview

The ELD3H7 and ELQ3H7 are phototransistor-based photocouplers (optocouplers) designed for electrical signal isolation. They consist of an infrared light-emitting diode (LED) optically coupled to a silicon phototransistor, all encapsulated within a compact surface-mount package. The primary function is to transmit electrical signals between two circuits while maintaining high electrical isolation, preventing noise, ground loops, and voltage spikes from propagating.

The ELD3H7 integrates 2 independent isolation channels within an 8-pin SSOP (Shrink Small Outline Package). The ELQ3H7 integrates 4 independent channels within a 16-pin SSOP. Both variants feature an ultra-low profile of 2.0 mm, making them suitable for space-constrained applications. The devices use a halogen-free, green molding compound and are compliant with Pb-free and RoHS directives.

2. Key Features and Core Advantages

• High Isolation Voltage: Rated at 3750 V_rms for 1 minute, ensuring robust protection and safety in high-voltage environments.
• Wide Current Transfer Ratio (CTR): Ranges from 50% to 600% at I_F = 5mA, V_CE = 5V, offering design flexibility for different signal amplification needs.
• Compact Form Factor: The SSOP package with a 2.0 mm profile is ideal for high-density PCB designs.
• Comprehensive Safety Approvals: Certified by UL (E214129), VDE (40028116), SEMKO, NEMKO, DEMKO, FIMKO, and CQC, facilitating use in globally regulated equipment.
• Fast Switching Characteristics: Typical rise time (t_r) of 5 µs and fall time (t_f) of 3 µs under specified test conditions, suitable for digital signal transmission.

3. Target Market and Applications

These photocouplers are engineered for applications requiring reliable signal isolation and noise immunity.

• DC-DC Converters: Providing feedback loop isolation in switch-mode power supplies.
• Programmable Logic Controllers (PLCs) & Industrial Automation: Isolating digital I/O signals between the controller and field devices.
• Telecommunication Equipment: Isolating signal lines in modems, interfaces, and network hardware.
• General Circuit Isolation: Transmitting signals between circuits of different ground potentials or impedance levels.

4. In-Depth Technical Parameter Analysis

4.1 Absolute Maximum Ratings

These are stress limits that must not be exceeded under any conditions to prevent permanent device damage.

• Input (LED Side): Forward current (I_F) 60 mA; Peak forward current (I_FP) 1 A for 1 µs pulse; Reverse voltage (V_R) 6 V; Power dissipation (P_D) 70 mW.
• Output (Transistor Side): Collector current (I_C) 50 mA; Collector-Emitter voltage (V_CEO) 80 V; Emitter-Collector voltage (V_ECO) 7 V; Power dissipation (P_C) 150 mW.
• Total Device: Total power dissipation (P_TOT) 200 mW; Isolation voltage (V_ISO) 3750 V_rms.
• Temperature: Operating range -55°C to +110°C; Storage range -55°C to +125°C; Soldering temperature 260°C for 10 seconds.

4.2 Electrical and Optoelectronic Characteristics

Typical performance parameters measured at 25°C.

4.2.1 Input (Infrared LED) Characteristics

• Forward Voltage (V_F): Typically 1.2V, maximum 1.4V at I_F=20mA. This parameter is crucial for designing the LED drive circuit.
• Reverse Current (I_R): Maximum 10 µA at V_R=4V, indicating good diode blocking characteristics.
• Input Capacitance (C_in): Typically 30 pF, affecting high-frequency switching performance.

4.2.2 Output (Phototransistor) Characteristics

• Dark Current (I_CEO): Maximum 100 nA at V_CE=20V with I_F=0mA. This is the leakage current when the LED is off, impacting the OFF-state signal integrity.
• Breakdown Voltages: BV_CEO ≥ 80V, BV_ECO ≥ 7V, defining the maximum allowable voltages across the transistor.
• Collector-Emitter Saturation Voltage (V_CE(sat)): Typically 0.1V, maximum 0.2V at I_F=10mA, I_C=1mA. A low V_CE(sat) is desirable for logic-level output.

4.2.3 Transfer Characteristics

• Current Transfer Ratio (CTR): Defined as (I_C / I_F) * 100%. The specified range is 50% to 600% at I_F=5mA, V_CE=5V. This wide binning allows selection based on required gain.
• Isolation Resistance (R_IO): Minimum 5×10¹⁰ Ω at 500V DC, ensuring excellent DC isolation.
• Isolation Capacitance (C_IO): Typically 0.3 pF, maximum 1.0 pF. A low capacitance minimizes capacitive coupling of high-frequency noise across the isolation barrier.
• Switching Times: Rise time (t_r) typically 5 µs, fall time (t_f) typically 3 µs under test conditions (V_CE=2V, I_C=2mA, R_L=100Ω). These values determine the maximum usable data rate.

5. Mechanical and Package Information

5.1 Package Dimensions and Outline Drawings

The devices are housed in SSOP packages. The ELD3H7 (2-channel) uses an 8-pin SSOP, while the ELQ3H7 (4-channel) uses a 16-pin SSOP. Both share a common low profile height of 2.0 mm. Detailed dimensional drawings with all critical measurements (body size, lead pitch, standoff) are provided in the datasheet for PCB footprint design.

5.2 Pin Configuration and Polarity

For ELD3H7 (8-pin):

• Pins 1, 3: Anode of Channel 1 and Channel 2 LEDs, respectively.
• Pins 2, 4: Cathode of Channel 1 and Channel 2 LEDs, respectively.
• Pins 5, 7: Emitter of Channel 1 and Channel 2 phototransistors, respectively.
• Pins 6, 8: Collector of Channel 1 and Channel 2 phototransistors, respectively.

For ELQ3H7 (16-pin):

• Pins 1, 3, 5, 7: Anode of Channels 1 to 4 LEDs.
• Pins 2, 4, 6, 8: Cathode of Channels 1 to 4 LEDs.
• Pins 9, 11, 13, 15: Emitter of Channels 1 to 4 phototransistors.
• Pins 10, 12, 14, 16: Collector of Channels 1 to 4 phototransistors.

5.3 Recommended PCB Pad Layout

The datasheet includes suggested land pattern designs for both the 8-pin and 16-pin SSOP packages. Adhering to these recommendations ensures reliable solder joint formation during reflow soldering and proper mechanical stability.

5.4 Device Marking

Devices are marked on the top surface. The marking includes:

• "EL": Manufacturer identifier.
• "D3H7" or "Q3H7": Device number for the 2-channel or 4-channel variant.
• "Y": A one-digit year code.
• "WW": A two-digit week code.
• "V": Optional marking indicating VDE approval.

6. Soldering and Assembly Guidelines

The devices are suitable for surface-mount assembly using reflow soldering techniques.

• Reflow Soldering: The maximum allowable soldering temperature is 260°C, measured at the package body, for a duration not exceeding 10 seconds. Standard lead-free reflow profiles (IPC/JEDEC J-STD-020) are applicable.
• Handling: Standard ESD (Electrostatic Discharge) precautions should be observed, as the device contains static-sensitive semiconductors.
• Cleaning: Follow standard PCB cleaning procedures compatible with the green epoxy molding compound.
• Storage: Store in a dry environment with temperature between -55°C and +125°C. Use within 12 months of the date code for optimal solderability.

7. Packaging and Ordering Information

7.1 Model Numbering System

The part number follows the format: EL[D3H7/Q3H7](Z)-V

• EL: Series prefix.
• D3H7 / Q3H7: Denotes the 2-channel or 4-channel device.
• (Z): Tape and reel packaging option. "TA" indicates tape and reel, while its absence indicates tube packaging.
• V: Optional suffix indicating VDE approval.

7.2 Packaging Specifications

• ELD3H7 (Tube): 80 units per tube.
• ELD3H7 (Tape & Reel): 1000 units per reel.
• ELQ3H7 (Tube): 40 units per tube.
• ELQ3H7 (Tape & Reel): 1000 units per reel.

The tape and reel specifications, including carrier tape width, pocket dimensions, and reel diameter, are detailed for automated pick-and-place machine setup.

8. Application Design Considerations

8.1 Typical Application Circuits

The most common application is digital signal isolation. A series current-limiting resistor must be connected to the LED anode to set the desired forward current (I_F). The value is calculated as R_limit = (V_{CC_input} - V_F) / I_F. On the output side, a pull-up resistor (R_L) is connected between the collector and the output side supply voltage (V_{CC_output}) to define the output logic levels and limit the phototransistor collector current.

8.2 Design Notes and Best Practices

• CTR Selection: Choose a CTR bin appropriate for your drive current and required output current. A higher CTR allows using a lower I_F for the same output, reducing input power.
• Speed vs. Current Trade-off: Switching speed (t_r, t_f) generally improves with higher I_F and lower R_L, but this increases power consumption. The test circuit (I_F pulse, V_CE=2V, I_C=2mA, R_L=100Ω) provides a reference for expected performance.
• Noise Immunity: The high isolation resistance (R_IO) and low isolation capacitance (C_IO) are key for rejecting common-mode noise. Ensure proper PCB layout to avoid creepage and clearance issues that could compromise the rated isolation voltage.
• Thermal Considerations: Do not exceed the total device power dissipation (P_TOT = 200 mW). Power is the sum of input LED power (I_F*V_F) and output transistor power (I_C*V_CE).

9. Technical Comparison and Differentiation

Compared to standard DIP-4 or DIP-6 photocouplers, the ELD3H7/ELQ3H7 series offers significant advantages:

• Size Reduction: The SSOP package occupies less than 25% of the board area of a standard DIP-8 package for a 2-channel device, enabling miniaturization.
• Multi-Channel Integration: The availability of 2 and 4 channels in single packages reduces component count and saves board space in multi-isolation applications.
• Profile: The 2.0 mm height is critical for ultra-thin designs.
• Performance: Maintains high isolation voltage and a wide CTR range despite the small size, a key differentiator from many miniaturized alternatives.

10. Frequently Asked Questions (FAQs)

10.1 What is the maximum data rate achievable with these photocouplers?

Based on the typical rise/fall times of 5 µs and 3 µs, the maximum practical data rate for a clean digital signal is approximately 1/(t_r+t_f) ≈ 125 kHz. For reliable operation, a conservative design target of 50-100 kHz is recommended.

10.2 How do I select the correct CTR bin for my application?

If your design requires a guaranteed minimum output current (I_C) with a specific input current (I_F), calculate the required minimum CTR: CTR_{min_req} = (I_C / I_F) * 100%. Select a device whose minimum guaranteed CTR (e.g., 50%) meets or exceeds this value. Using a higher CTR bin provides more design margin.

10.3 Can these devices be used to isolate analog signals?

While primarily designed for digital isolation, they can be used in low-frequency, low-precision analog applications (e.g., feedback in isolated power supplies). However, the CTR has a strong temperature dependence and nonlinearity with I_F, which makes them unsuitable for precision analog signal transmission without extensive calibration or compensation circuits. Specialized linear optocouplers are better suited for analog isolation.

10.4 What is the purpose of the isolation voltage rating, and how is it tested?

The 3750 V_rms rating (for 1 minute) is a safety specification indicating the dielectric strength of the insulation between the input and output sides. During testing, all pins on the LED side are shorted together, and all pins on the transistor side are shorted together. A high AC voltage is applied between these two groups. This rating ensures protection against high-voltage transients that may occur in industrial or mains-connected equipment.

11. Practical Design Example

Scenario: Isolating a 3.3V digital signal from a microcontroller to a 5V system.

• Input Side: V_{CC_input} = 3.3V. Target I_F = 5 mA for good speed and CTR. Assuming V_F ≈ 1.2V, R_limit = (3.3V - 1.2V) / 0.005A = 420Ω. Use a standard 430Ω resistor.
• Output Side: V_{CC_output} = 5V. Choose R_L to limit I_C and set logic levels. For a CTR of 100% at I_F=5mA, I_C ≈ 5mA. When the transistor is ON (saturated), V_CE ≈ 0.1V, so the output is low (~0.1V). When OFF, the output is pulled high to 5V. The power in R_L when ON is (5V - 0.1V) * 5mA ≈ 24.5 mW, well within ratings. A standard 1 kΩ resistor would give I_C ≈ (5V - 0.1V)/1kΩ = 4.9mA, which is also acceptable.
• Layout: Place the device close to the isolation barrier on the PCB. Maintain recommended creepage and clearance distances (consult safety standards like IEC 60950-1) between the input and output copper traces, especially for the high isolation voltage rating.

12. Operating Principle

A photocoupler operates by converting an electrical signal into light, transmitting it across an electrically insulating gap, and then converting the light back into an electrical signal. In the ELD3H7/ELQ3H7:

1. An electrical current (I_F) flows through the infrared LED, causing it to emit photons.
2. These photons travel through a transparent insulating dielectric (the molding compound) and strike the base region of the silicon phototransistor.
3. The photon energy generates electron-hole pairs in the base, effectively creating a base current that turns the transistor ON.
4. The transistor conducts a collector current (I_C) that is proportional to the intensity of the received light, and hence to the input I_F. The proportionality constant is the CTR.

The key is that the only connection between input and output is optical, providing the electrical isolation.

13. Industry Trends and Development

The trend in optocoupler technology is driven by demands for higher speed, smaller size, lower power consumption, and integration of additional features. While traditional phototransistor couplers like the ELD3H7/ELQ3H7 excel in cost-effectiveness, robustness, and high isolation voltage, newer technologies are emerging:

• High-Speed Digital Couplers: Utilize CMOS technology and integrated LEDs to achieve data rates in the tens or hundreds of Mbps, far exceeding phototransistor-based devices.
• Integrated Isolated Functions: Devices that combine isolation with functions like isolated gate drivers, isolated ADCs, or isolated power delivery (isoPower).
• Enhanced Safety and Reliability: Ongoing development focuses on improving isolation material durability, surge immunity, and achieving higher working voltage ratings in smaller packages to meet evolving international safety standards.

Phototransistor couplers remain a fundamental and widely used solution for cost-sensitive, general-purpose isolation where moderate speed and high reliability are paramount.