ITR20403 Opto Interrupter Datasheet - Package 4.0x3.0x2.0mm - Forward Voltage 1.6V - Power Dissipation 75mW - Infrared 940nm - English Technical Document

1. Product Overview

The ITR20403 is a compact opto interrupter module designed for non-contact sensing applications. It integrates an infrared emitting diode (IRED) and a silicon phototransistor within a single, small-form-factor black thermoplastic housing. The primary function of the device is to detect the interruption of an infrared light beam between its emitter and receiver components.

1.1 Core Advantages and Target Market

The device offers several key advantages that make it suitable for precision applications. Its fast response time and high sensitivity enable reliable detection of rapid object movements. The thin and small package facilitates integration into space-constrained designs commonly found in consumer electronics and office automation equipment. A significant technical feature is the housing design, which allows the phototransistor to receive radiation primarily from the integrated IR LED, thereby minimizing interference and noise from ambient light sources. The primary target markets include imaging devices, document handling systems, and various automation controls requiring accurate position or presence detection.

2. In-Depth Technical Parameter Analysis

This section provides a detailed, objective interpretation of the device's electrical, optical, and thermal specifications as defined in the datasheet.

2.1 Absolute Maximum Ratings

The absolute maximum ratings define the stress limits beyond which permanent damage to the device may occur. These are not recommended operating conditions.

• Input (IRED) Power Dissipation (Pd): 75 mW maximum at or below 25\u00b0C free air temperature. Exceeding this limit risks thermal damage to the LED chip.
• Input Reverse Voltage (VR): 5 V maximum. Applying a higher reverse voltage can cause junction breakdown.
• Continuous Forward Current (IF): 50 mA maximum. This is the highest DC current the IRED can withstand.
• Output (Phototransistor) Power Dissipation (Pd): 75 mW maximum at or below 25\u00b0C.
• Collector Current (IC): 20 mA maximum for the phototransistor output.
• Collector-Emitter Voltage (BV_CEO): 30 V maximum. This is the breakdown voltage with the base open.
• Operating Temperature (T_opr): -25\u00b0C to +80\u00b0C. The device is guaranteed to function within this ambient temperature range.
• Storage Temperature (T_stg): -40\u00b0C to +85\u00b0C.
• Lead Soldering Temperature (T_sol): 260\u00b0C maximum for 5 seconds, measured 3mm from the package body. This is critical for assembly process control.

2.2 Electro-Optical Characteristics

These parameters are measured under standard test conditions (Ta=25\u00b0C) and represent typical device performance.

• Forward Voltage (V_F): Typically 1.23V, with a maximum of 1.6V at I_F=20mA. This parameter is essential for designing the current-limiting driver circuit for the IRED.
• Peak Wavelength (\u03bb_P): 940 nm. This is the nominal wavelength of the infrared light emitted, which matches the peak sensitivity of the receiving phototransistor.
• Collector Dark Current (I_CEO): Maximum 100 nA at V_CE=20V with zero illumination. This leakage current determines the noise floor of the sensor in the "off" state.
• Collector-Emitter Saturation Voltage (V_CE(sat)): Maximum 0.4V at I_C=2mA and an irradiance (E_e) of 1 mW/cm\u00b2. A low saturation voltage is desirable for digital switching applications.
• On-State Collector Current (I_C(on)): Ranges from a minimum of 0.2 mA to a maximum of 5.0 mA under the test conditions of V_CE=5V and I_F=20mA. This wide range indicates the transfer ratio (CTR) variation between devices, which must be accounted for in circuit design.
• Rise/Fall Time (t_r, t_f): Typically 15 \u00b5sec each under specified switching conditions. This defines the maximum achievable switching frequency for the device.

3. Performance Curve Analysis

The datasheet includes typical characteristic curves that provide insight into device behavior under varying conditions.

3.1 Forward Current vs. Ambient Temperature

This curve illustrates the necessary derating of the IRED's forward current as ambient temperature increases. To prevent exceeding the maximum junction temperature and ensure long-term reliability, the operating current must be reduced when the device is used in high-temperature environments. Designers must consult this graph to determine the safe operating current for their specific application's maximum ambient temperature.

3.2 Spectral Sensitivity

Separate spectral sensitivity curves are provided for both the IR emitter and the phototransistor. The IRED curve shows the relative radiant intensity versus wavelength, peaking at 940 nm. The phototransistor curve shows its relative response versus incident light wavelength, with a peak designed to align with the emitter's output. The narrow, matched response minimizes sensitivity to visible ambient light, a key feature for stable operation in varying lighting conditions.

3.3 Forward Current vs. Forward Voltage

This IV curve for the IRED shows the non-linear relationship between forward voltage and current. It is crucial for selecting an appropriate current-limiting scheme (e.g., resistor, constant current source) to ensure stable IR output over the operating temperature range and across production variances.

4. Mechanical and Packaging Information

4.1 Package Dimensions

The device is housed in a compact package. Key dimensions include a body width of approximately 4.0 mm, a depth of 3.0 mm, and a height of 2.0 mm. The lead spacing is 2.54 mm (0.1 inches), which is a standard pitch for through-hole PCB mounting. All dimensional tolerances are \u00b10.25 mm unless otherwise specified. The leads are measured where they emerge from the package body.

4.2 Polarity Identification and Mounting

The component has four leads. Standard convention for such opto interrupters is that the two leads on one side belong to the infrared emitter (anode and cathode), and the two on the opposite side belong to the phototransistor (emitter and collector). The exact pinout must be verified from the package diagram. When mounting, the PCB holes must be precisely aligned with the lead positions to avoid imposing mechanical stress on the epoxy body during insertion, which can degrade performance or cause failure.

5. Soldering and Assembly Guidelines

Proper handling is critical to maintaining device integrity and performance.

5.1 Lead Forming

If lead bending is required, it must be performed before soldering. The bend should be made at a distance greater than 3 mm from the bottom of the epoxy package body. The lead frame must be securely held during bending to prevent stress from being transmitted to the fragile epoxy bulb, which could cause cracking or internal damage. Cutting of leads should be done at room temperature.

5.2 Soldering Process

A minimum distance of 3 mm must be maintained between the solder joint and the epoxy bulb. Recommended conditions are:

• Hand Soldering: Iron tip temperature maximum 300\u00b0C (for a 30W iron), soldering time maximum 3 seconds per lead.
• Wave/Dip Soldering: Preheat temperature maximum 100\u00b0C for up to 60 seconds. Solder bath temperature maximum 260\u00b0C with a dwell time of 5 seconds maximum.

Avoid applying any mechanical stress to the leads while the device is at elevated temperature. Dip or hand soldering should not be performed more than once. After soldering, the device should be protected from mechanical shock or vibration until it returns to room temperature. Rapid cooling processes are not recommended.

5.3 Cleaning and Storage

Ultrasonic cleaning is prohibited, as the high-frequency vibrations can damage the internal components or the epoxy seal. For storage, devices should be kept at 10-30\u00b0C and 70% RH or less for up to 3 months after shipment. For longer storage (up to one year), a sealed container with a nitrogen atmosphere at 10-25\u00b0C and 20-60% RH is recommended. After opening the moisture-sensitive packaging, devices should be used within 24 hours or as soon as possible, with any remaining components resealed promptly.

6. Packaging and Ordering Information

The standard packing specification is 120 pieces per tube, 96 tubes per box, and 2 boxes per carton. The label on the packaging includes fields for Customer Part Number (CPN), Manufacturer Part Number (P/N), Packing Quantity (QTY), Reference (REF), and Lot Number (LOT No.).

7. Application Suggestions

7.1 Typical Application Scenarios

• Paper Detection in Printers/Copiers/Scanners: Detecting the presence of paper, paper jams, or the leading/trailing edge of a document.
• Lens Cover or Filter Position Detection in Cameras: Sensing whether a lens cap is on or if a filter wheel is in the correct position.
• Non-contact End-stop Sensing: Used in scanners, plotters, or automated stages to detect the home or limit position without physical contact.
• Object Counting or Sorting: Detecting objects on a conveyor belt as they break the infrared beam.
• Rotary Encoder Disk Sensing: Reading slots in a rotating disk to measure speed or position (though dedicated encoder modules are often more suitable for high-resolution tasks).

7.2 Design Considerations and Circuit Interface

When designing with the ITR20403, several factors must be considered:

1. Current Limiting for the IRED: A series resistor must be calculated based on the supply voltage (V_CC), the desired forward current (I_F, typically 20mA for rated output), and the forward voltage drop (V_F ~1.23V). R = (V_CC - V_F) / I_F.
2. Output Interface Circuit: The phototransistor can be used in two common configurations:
   • Switch Mode: Connect a pull-up resistor (e.g., 1k\u03a9 to 10k\u03a9) from the collector to V_CC. The emitter is connected to ground. The output at the collector will be low (near V_CE(sat)) when the beam is unblocked (transistor ON) and high (V_CC) when the beam is blocked (transistor OFF).
   • Analog Mode: The phototransistor can be used in a common-emitter configuration with a collector resistor to produce a voltage proportional to light intensity. However, the non-linear response and temperature dependence make it less ideal for precise analog measurements compared to photodiodes with op-amp circuits.
3. Noise Immunity: Although resistant to ambient light, the circuit may still pick up electrical noise. Bypass capacitors (0.1 \u00b5F) near the device's power pins and careful PCB layout are recommended. For long cable runs or noisy environments, shielding or using the output to drive a Schmitt trigger input can improve reliability.
4. Aperture and Slot Design: The object interrupting the beam should be opaque to infrared. The resolution and repeatability of detection depend on the width of the object relative to the slot width in the device's housing. For edge detection, a vane or flag with a sharp edge provides the most precise timing.

8. Technical Comparison and Differentiation

The ITR20403 differentiates itself primarily through its compact, thin form factor, which is advantageous in miniaturized consumer electronics. Its fast 15 \u00b5s response time is suitable for detecting moderately high-speed events. The integrated housing that spectrally matches the emitter and receiver provides inherent ambient light rejection, a feature that simplifies design compared to using discrete components. When compared to reflective object sensors, interrupters offer higher positional accuracy and are less sensitive to the color or reflectivity of the target object. Compared to slotted optical switches with wider gaps, this device's narrow gap allows for detection of smaller objects or more precise edge detection.

9. Frequently Asked Questions (Based on Technical Parameters)

9.1 What is the typical operating current for the IR LED?

The electro-optical characteristics are tested at I_F = 20 mA, which is a common and recommended operating point to achieve the specified on-state collector current. The circuit must be designed to not exceed the absolute maximum rating of 50 mA.

9.2 Why is there such a wide range (0.2mA to 5.0mA) for the On-State Collector Current?

This range represents the device-to-device variation in the Current Transfer Ratio (CTR), which is the ratio of phototransistor output current (I_C) to IRED input current (I_F). This variation is inherent in the manufacturing process of optocouplers and interrupters. The circuit must be designed to function correctly with the minimum specified I_C(on) (0.2mA) to ensure reliability across all production units.

9.3 Can this sensor be used outdoors?

While the housing provides good ambient light rejection, direct sunlight contains significant infrared radiation that could saturate the sensor. For outdoor use, additional optical filtering, shielding, or pulsed operation with synchronous detection would be necessary for reliable performance. The operating temperature range (-25\u00b0C to +80\u00b0C) also limits extreme environment applications.

9.4 How close does an object need to be to interrupt the beam?

The device has a narrow, focused gap. An object needs to physically pass through the slot between the emitter and detector. There is no "proximity" sensing capability; the beam must be fully occluded for the output state to change reliably.

10. Design and Usage Case Study

Scenario: Paper-Out Sensor in a Desktop Printer.

Implementation: The ITR20403 is mounted on the printer's paper feed path. A lever or flag, attached to a spring, rests in the sensor's slot when no paper is present. When a sheet of paper is fed, it pushes the flag out of the slot, allowing the infrared beam to pass and turning the phototransistor ON.

Circuit Design: The IRED is driven with 20mA via a current-limiting resistor from the printer's 5V logic supply. The phototransistor collector is connected to a 3.3V microcontroller input pin through a 4.7k\u03a9 pull-up resistor. The emitter is grounded.

Software Logic: The microcontroller pin is configured as a digital input. A LOW reading indicates the beam is unblocked (flag out, paper present). A HIGH reading indicates the beam is blocked (flag in, no paper), triggering a "Paper Out" alert to the user. Debouncing logic (e.g., in software) is added to ignore mechanical vibrations of the flag.

Key Considerations for this Case: The flag mechanism must be designed to reliably and fully enter the sensor slot. The spring must provide enough force for positive return but not so much that it damages the paper or causes wear on the sensor. The sensor's position must be fixed securely to maintain alignment.

11. Operational Principle

The ITR20403 operates on the principle of modulated light transmission and detection. An infrared light-emitting diode (IRED) is forward-biased with a constant current, causing it to emit photons at a peak wavelength of 940 nm. Directly opposite, within the same housing, is a silicon NPN phototransistor. When the infrared beam travels unobstructed across the gap, it strikes the base region of the phototransistor. The absorbed photons generate electron-hole pairs, which act as base current, turning the transistor ON and allowing a collector current (I_C) to flow that is proportional to the light intensity. When an opaque object enters the gap, it blocks the beam, the photogenerated base current ceases, and the transistor turns OFF. The output circuit converts this ON/OFF state change into a usable electrical signal. The black thermoplastic housing serves to contain the light path, prevent optical crosstalk, and block most ambient visible light, whose photons generally do not have enough energy to be absorbed by the silicon phototransistor's bandgap, thus providing inherent optical filtering.

12. Technology Trends

Opto interrupters like the ITR20403 represent a mature and reliable technology. Current trends in the field focus on several areas: further miniaturization to enable integration into ever-smaller portable and wearable devices; the development of surface-mount device (SMD) versions with improved reflow soldering compatibility for automated assembly; increased switching speeds to support higher data rates in encoder applications or faster machinery; and enhanced robustness against environmental factors like higher temperature, humidity, and contamination. There is also a trend towards integrating additional functionality, such as built-in Schmitt triggers on the output for hysteresis or even digital interfaces (I2C, SPI) for smarter, addressable sensor modules. However, the basic through-hole, discrete component design, as seen in the ITR20403, remains highly cost-effective and widely used in applications where its performance and form factor are sufficient.