6N137 EL26XX Series Photocoupler Datasheet - 8-Pin DIP Package - High Speed 10Mbit/s - 5000Vrms Isolation - English Technical Document

1. Product Overview

The 6N137, EL2601, and EL2611 are high-speed, logic gate output photocouplers (optoisolators). These devices consist of an infrared light-emitting diode (LED) optically coupled to a high-speed integrated photodetector with a strobable output. They are designed for applications requiring electrical isolation and high-speed digital signal transmission.

1.1 Core Advantages and Positioning

The primary advantage of this series is its combination of high-speed performance and robust isolation. With a data rate of up to 10 Mbit/s, it is suitable for modern digital communication interfaces. The devices offer a high common-mode transient immunity (CMTI), with the EL2611 variant rated for a minimum of 10 kV/μs, making them ideal for noisy industrial environments. The logic gate output simplifies interface with standard logic families like TTL and CMOS.

1.2 Target Applications

These photocouplers are targeted at applications requiring ground loop elimination, signal isolation in data transmission systems, and noise immunity in power electronics. Common use cases include:

• Isolation in switching power supplies and motor drives.
• Data line receivers and multiplexing systems.
• Replacement for pulse transformers in digital circuits.
• Computer peripheral interfaces and industrial control systems.
• General-purpose high-speed logic isolation.

2. In-Depth Technical Parameter Analysis

The following sections provide a detailed breakdown of the device's electrical and switching characteristics.

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage may occur. Key parameters include:

• Input Forward Current (I_F): 50 mA maximum.
• Supply Voltage (V_CC): 7.0 V maximum.
• Output Voltage (V_O): 7.0 V maximum.
• Isolation Voltage (V_ISO): 5000 V_rms for 1 minute (test condition: pins 1-4 shorted together, pins 5-8 shorted together).
• Operating Temperature (T_OPR): -40°C to +85°C.
• Storage Temperature (T_STG): -55°C to +125°C.

2.2 Electrical Characteristics (Input)

Parameters related to the input infrared LED:

• Forward Voltage (V_F): Typically 1.4V, maximum 1.8V at I_F = 10 mA.
• Reverse Voltage (V_R): 5.0 V maximum.
• Temperature Coefficient of V_F: Approximately -1.8 mV/°C.
• Input Capacitance (C_IN): Typically 60 pF.

2.3 Electrical Characteristics (Output & Transfer)

Parameters related to the output detector and the overall signal transfer:

• Supply Current (High/Low): I_CCH (output high) is typically 7 mA (max 10 mA). I_CCL (output low) is typically 9 mA (max 13 mA).
• Enable Input Currents: I_EH and I_EL are typically below 1.6 mA.
• Low-Level Output Voltage (V_OL): Typically 0.35V, maximum 0.6V under specified load conditions (I_CL=13mA). This is a critical parameter for logic-level compatibility.
• Input Threshold Current (I_FT): The LED current required to guarantee a logic-low output is typically 2.5 mA, maximum 5 mA.

2.4 Switching Characteristics

These parameters define the speed performance of the photocoupler, measured under standard conditions (V_CC=5V, I_F=7.5mA, C_L=15pF, R_L=350Ω).

• Propagation Delay (t_PHL, t_PLH): Typically 35-40 ns, with a maximum of 75 ns for both high-to-low and low-to-high transitions. This enables the 10 Mbit/s data rate.
• Pulse Width Distortion: |t_PHL - t_PLH| is typically 5 ns, maximum 35 ns. Lower distortion is better for preserving signal integrity.
• Rise/Fall Times (t_r, t_f): Output rise time is typically 40 ns, while fall time is typically a faster 10 ns.
• Enable Propagation Delay: The delay from the enable (V_E) pin to the output is typically 15 ns.
• Common-Mode Transient Immunity (CMTI): This is a key differentiator. The 6N137 has no specified minimum. The EL2601 guarantees 5,000 V/μs. The EL2611 guarantees 10,000 V/μs under standard test and 20,000 V/μs with the recommended drive circuit (Fig. 15). High CMTI prevents noise from coupling across the isolation barrier.

3. Mechanical and Package Information

3.1 Pin Configuration (8-Pin DIP)

The device is offered in a standard 8-pin Dual In-line Package (DIP).

1. No Connection (NC)
2. Anode (A) of input LED
3. Cathode (K) of input LED
4. No Connection (NC)
5. Ground (GND) for output side
6. Output (V_OUT)
7. Enable Input (V_E)
8. Supply Voltage (V_CC) for output side

3.2 Package Options

The datasheet mentions availability in wide-lead spacing and Surface-Mount Device (SMD) options, though specific package codes (e.g., SOIC-8) are not detailed in the provided excerpt.

4. Application Guidelines and Design Considerations

4.1 Critical Design Rules

• Bypass Capacitor: A 0.1 μF (or larger) capacitor with good high-frequency characteristics (ceramic or solid tantalum) must be connected between pins 8 (V_CC) and 5 (GND), placed as close as possible to the device. This is essential for stable operation and minimizing noise.
• Enable Pin: The enable input (pin 7) has an internal pull-up resistor, so no external resistor is required. Driving it low (<0.8V) enables the output. Driving it high (>2.0V) forces the output high, regardless of the input LED state.
• Input Current: To ensure proper switching, the input LED current should be set according to the required speed and the I_FT parameter. A typical operating current is 7.5-10 mA.
• Output Load: The standard test condition uses a 350Ω pull-up resistor to V_CC. This value should be used as a reference for circuit design to meet the specified switching times.

4.2 Truth Table (Positive Logic)

The device functions as a non-inverting buffer when enabled. The truth table is as follows:

4.3 Recommended Circuit for High CMTI (EL2611)

Figure 15 in the datasheet shows a specific drive circuit recommended for the EL2611 family to achieve its highest specified CMTI of 20,000 V/μs. This circuit typically involves careful management of the input LED drive path to minimize parasitic coupling.

5. Performance Curves and Typical Characteristics

The datasheet includes a section for \"Typical Electro-Optical Characteristics Curves.\" While the specific graphs are not provided in the text excerpt, such curves typically illustrate relationships critical for design:

• Current Transfer Ratio (CTR) vs. Forward Current: Shows the efficiency of the optical coupling.
• Propagation Delay vs. Forward Current: Demonstrates how speed varies with LED drive current.
• Output Voltage vs. Temperature: Indicates thermal stability of the output logic levels.
• Common-Mode Transient Immunity vs. Frequency: Shows the CMTI performance across different noise frequencies.

Designers should consult these graphs to optimize performance for their specific operating conditions (temperature, required speed).

6. Soldering and Handling

The Absolute Maximum Ratings specify a soldering temperature (T_SOL) of 260°C for 10 seconds. This aligns with typical lead-free reflow soldering profiles. Standard ESD (Electrostatic Discharge) precautions should be observed when handling these semiconductor devices.

7. Technical Comparison and Selection Guide

The 6N137, EL2601, and EL2611 share a common pinout and core functionality but differ in a key specification:

• 6N137: Base high-speed model. CMTI is not guaranteed to a specific minimum level.
• EL2601: Enhanced model with a guaranteed minimum CMTI of 5,000 V/μs.
• EL2611: Premium model with a guaranteed minimum CMTI of 10,000 V/μs (20,000 V/μs with recommended circuit).

Selection Advice: For general-purpose digital isolation in benign environments, the 6N137 may be sufficient. For industrial motor drives, power inverters, or any environment with high-voltage switching noise (dV/dt), the EL2601 or EL2611 should be selected based on the noise immunity required. The EL2611 with its specialized drive circuit offers the highest robustness.

8. Principle of Operation

A photocoupler provides galvanic isolation by using light as the signal transmission medium. An electrical signal drives the input Infrared LED, causing it to emit light. This light crosses an isolation gap (often a transparent dielectric) and strikes a photodetector integrated with a logic gate circuit on the output side. The detector converts the light back into an electrical signal, which is then conditioned by the logic gate (with enable/disable functionality) to produce a clean digital output. The physical separation between the LED and the detector provides the high isolation voltage rating.

9. Frequently Asked Questions (FAQs)

Q: What is the purpose of the enable (V_E) pin?

A: The enable pin allows the output to be forced into a high state, effectively muting the signal from the input. This can be useful for bus sharing, fault conditions, or power-saving modes.

Q: Can I drive the input LED directly from a microcontroller pin?

A: Possibly, but it depends on the microcontroller's output current capability and voltage. The typical V_F is 1.4V at 10 mA. A series current-limiting resistor is always required. Ensure the MCU pin can source/sink the required I_F (e.g., 7.5-10 mA for full speed).

Q: Why is the bypass capacitor so critical?

A> The high-speed switching of the internal detector circuit can cause sudden current spikes on the V_CC line. The local bypass capacitor supplies this transient current, preventing voltage droops that could cause output glitches or false triggering, and also helps shunt high-frequency noise.

Q: How do I choose between the 6N137, EL2601, and EL2611?

A: The primary differentiator is Common-Mode Transient Immunity (CMTI). If your application involves significant voltage swings across the isolation barrier (e.g., in a motor drive), choose the EL2601 or EL2611. For simple digital isolation in low-noise settings, the 6N137 may be adequate. Always refer to the specific CMTI requirements of your system.

10. Application Examples and Use Cases

Case 1: Isolated RS-485/422 Interface: The photocoupler can be used to isolate the data lines (TxD, RxD) and/or the direction control line of a UART-to-RS485 transceiver. This breaks ground loops and protects the sensitive logic side from faults on the long bus lines. The high speed ensures no bottleneck in data throughput.

Case 2: Gate Drive Isolation in a Switch-Mode Power Supply (SMPS): In a half-bridge or full-bridge topology, the high-side MOSFET/IGBT gate driver needs a signal referenced to a floating switch node. A photocoupler like the EL2611 can transmit the PWM control signal from the low-side controller to the high-side driver, providing both level shifting and isolation. Its high CMTI is crucial to ignore the large dV/dt noise from the switching node.

Case 3: Digital Input Module for PLC: Industrial Programmable Logic Controllers (PLCs) read signals from sensors and switches in harsh environments. Photocouplers are used on every digital input channel to isolate the field wiring (24V sensors) from the internal PLC logic (3.3V/5V). They provide protection against overvoltage, noise, and wiring errors.