PD15-21B/TR8 Silicon PIN Photodiode Datasheet - 1206 Package (1.6x0.8x0.55mm) - Spectral Range 730-1100nm - Peak 940nm - English Technical Document

1. Product Overview

The PD15-21B/TR8 is a high-performance Silicon PIN photodiode housed in a miniature surface-mount device (SMD) package. This component is specifically designed for sensing applications within the infrared spectrum, offering a compact and reliable solution for modern electronic designs requiring optical detection.

1.1 Core Advantages and Product Positioning

This device is engineered to provide several key benefits essential for precision sensing. It features a fast response time, enabling it to detect rapid changes in light intensity, which is critical for applications like counting, sorting, and position sensing. The high photo sensitivity ensures reliable signal detection even under low illumination conditions. Furthermore, the small junction capacitance contributes to its high-speed performance. The product is supplied in industry-standard 8mm tape on 7-inch diameter reels, facilitating automated assembly processes. It is fully compliant with environmental regulations, being Pb-free, RoHS compliant, EU REACH compliant, and halogen-free (with Bromine <900 ppm, Chlorine <900 ppm, and their sum <1500 ppm).

1.2 Target Market and Applications

The primary target markets include industrial automation, consumer electronics, and safety systems. Its miniature size and SMD format make it ideal for space-constrained applications. Typical use cases include:

• Miniature Optical Switches: Used in object detection, paper detection in printers, and slot sensors.
• Counters and Sorters: Employed in assembly lines for part counting and sorting based on presence/absence detection.
• Position Sensors: Utilized for edge detection, limit switching, and rotary encoder systems.
• Infrared Applied Systems: Integral part of systems using infrared emitters for data transmission, proximity sensing, and ambient light sensing.

2. In-Depth Technical Parameter Analysis

A thorough understanding of the device's specifications is crucial for proper circuit design and system integration.

2.1 Absolute Maximum Ratings

These ratings define the limits beyond which permanent damage to the device may occur. Operating the device continuously at or near these limits is not recommended.

• Reverse Voltage (V_R): 32 V. This is the maximum voltage that can be applied in reverse bias across the photodiode terminals.
• Operating Temperature (T_opr): -25°C to +85°C. The ambient temperature range for reliable operation.
• Storage Temperature (T_stg): -40°C to +85°C. The temperature range for non-operational storage.
• Soldering Temperature (T_sol): 260°C for a maximum of 5 seconds. This defines the peak reflow profile temperature.
• Power Dissipation (P_d): 150 mW at or below 25°C free air temperature. This limits the total electrical power the device can safely handle.

2.2 Electro-Optical Characteristics

These parameters, measured at a standard temperature of 25°C, define the core sensing performance of the photodiode.

• Spectral Bandwidth (λ_0.5): 730 nm to 1100 nm. This is the wavelength range where the photodiode's responsivity is at least half of its peak value. It indicates sensitivity to near-infrared light.
• Peak Sensitivity Wavelength (λ_P): 940 nm (typical). The device is spectrally matched to common infrared emitting diodes (IREDs) operating at this wavelength, maximizing system efficiency.
• Short-Circuit Current (I_SC): 0.8 μA (typical) under an irradiance (E_e) of 1 mW/cm² at 940 nm. This is the photocurrent generated when the photodiode is operated in photovoltaic mode (zero bias).
• Reverse Light Current (I_L): 0.2 μA (min) to 0.8 μA (typical) under an irradiance of 1 mW/cm² at 940 nm with a reverse bias voltage (V_R) of 5V. This parameter is relevant for photoconductive mode operation, where an external reverse bias is applied to improve speed and linearity.
• Dark Current (I_D): 10 nA (max) with V_R=10V in complete darkness (E_e=0). This is the small leakage current that flows even when no light is present. A low dark current is essential for good signal-to-noise ratio, especially in low-light applications.
• Reverse Breakdown Voltage (BV_R): 32 V (min), 170 V (typical) measured at a reverse current of 100 μA. This indicates a very high breakdown voltage, providing a wide operating margin below the absolute maximum rating of 32V.

3. Performance Curve Analysis

The datasheet provides several characteristic curves that illustrate how key parameters vary with operating conditions.

3.1 Power Derating

Fig.1: Power Dissipation vs. Ambient Temperature shows how the maximum allowable power dissipation decreases as the ambient temperature increases above 25°C. Designers must derate the power accordingly to prevent thermal overstress.

3.2 Spectral Response

Fig.2: Spectral Sensitivity graphically depicts the relative responsivity of the photodiode across the light spectrum, confirming its peak at 940 nm and the defined 730-1100 nm bandwidth.

3.3 Temperature Dependence

Fig.3: Dark Current vs. Ambient Temperature illustrates that dark current approximately doubles for every 10°C rise in temperature. This is a fundamental semiconductor behavior and must be considered in high-temperature or precision applications. Fig.4: Reverse Light Current vs. Irradiance (E_e) demonstrates the linear relationship between incident light power and generated photocurrent, a key characteristic of PIN photodiodes.

3.4 Angular Response

Fig.5: Relative Radiant Intensity vs. Angular Displacement shows the directional sensitivity of the device. The black epoxy package with a spherical lens provides a specific viewing angle, which influences how the photodiode should be aligned with a light source in the system design.

4. Mechanical and Package Information

4.1 Package Dimensions

The device conforms to the standard 1206 (3216 metric) SMD footprint: approximately 1.6mm in length, 0.8mm in width, and 0.55mm in height (excluding the lens dome). Detailed dimensional drawings with tolerances of ±0.1mm are provided for PCB land pattern design. A suggested pad layout is given as a reference, but designers are advised to modify it based on their specific PCB manufacturing process and thermal requirements.

4.2 Polarity Identification

The photodiode is molded in black epoxy. The cathode terminal is typically marked or identified in the package outline drawing. Correct polarity connection is essential for proper operation in reverse-bias (photoconductive) mode.

5. Soldering and Assembly Guidelines

Proper handling is critical to maintain device reliability and performance.

5.1 Storage and Moisture Sensitivity

The device is moisture-sensitive. The moisture barrier bag should not be opened until ready for use. After opening, the "floor life" is 168 hours (7 days) when stored at 10-30°C and ≤60% RH. Unused devices must be rebagged with desiccant. If the floor life is exceeded or the desiccant indicates moisture absorption, baking at 60°C ±5°C and <5% RH for 96 hours is required before use.

5.2 Reflow Soldering

A Pb-free solder temperature profile is recommended, with a peak temperature of 260°C for a maximum of 5 seconds. Reflow soldering should not be performed more than two times. Stress on the component body during heating and warping of the PCB after soldering must be avoided.

5.3 Hand Soldering and Rework

If hand soldering is necessary, use a soldering iron with a tip temperature below 350°C and a capacity of 25W or less. Contact time per terminal should be under 3 seconds, with intervals of more than 2 seconds between soldering each terminal. Rework is strongly discouraged. If unavoidable, a specialized double-head soldering iron must be used to simultaneously heat both terminals, and the effect on device characteristics must be verified beforehand.

6. Packaging and Ordering Information

6.1 Tape and Reel Specifications

The product is supplied in 8mm wide embossed carrier tape on 7-inch (178mm) diameter reels. Each reel contains 2000 pieces. Detailed carrier tape and reel dimensions are provided to ensure compatibility with automated pick-and-place equipment.

6.2 Label Specification

The reel label includes standard information such as Customer Part Number (CPN), Manufacturer Part Number (P/N), Lot Number, Quantity, Peak Wavelength (HUE), Ranks (CAT), Reference (REF), Moisture Sensitivity Level (MSL-X), and Country of Manufacture.

7. Application Design Considerations

7.1 Circuit Protection

Critical Note: The datasheet explicitly warns that an external current-limiting resistor must be used in series with the photodiode. Without this resistor, a slight voltage shift can cause a large current change, potentially leading to immediate burnout of the device. The resistor value must be calculated based on the supply voltage and the maximum expected photocurrent.

7.2 Biasing Modes

The photodiode can be used in two primary modes:

1. Photovoltaic (Zero-Bias) Mode: The photodiode generates a voltage/current when illuminated, with no external bias applied. This mode offers very low dark current and noise but has slower response times.
2. Photoconductive (Reverse-Bias) Mode: An external reverse voltage is applied (e.g., 5V as in the test condition). This widens the depletion region, reducing junction capacitance and thus increasing speed and bandwidth. It also improves linearity but increases dark current.

The choice depends on the application's requirement for speed versus noise performance.

7.3 Interfacing with Amplifiers

For amplifying the small photocurrent (μA range), a transimpedance amplifier (TIA) circuit is commonly used. This circuit converts the photodiode current into a proportional output voltage. Key design considerations for the TIA include selecting an operational amplifier with low input bias current and low noise, and calculating the feedback resistor and capacitor for the desired gain and bandwidth while maintaining stability.

8. Technical Comparison and Differentiation

Compared to phototransistors, this Silicon PIN photodiode offers superior speed and linearity due to its intrinsic region, which reduces capacitance. Its response is purely dependent on incident light, unlike a phototransistor which has current gain and can be slower and less linear. Compared to other photodiodes, its 1206 package offers a good balance between miniaturization and ease of handling/assembly, while its high breakdown voltage and specific spectral matching to 940nm IREDs are distinct advantages for targeted infrared sensing applications.

9. Frequently Asked Questions (FAQ)

9.1 What is the difference between I_SC and I_L?

I_SC (Short-Circuit Current) is measured with zero volts across the diode (photovoltaic mode). I_L (Reverse Light Current) is measured with an applied reverse bias voltage (photoconductive mode). I_L is typically very close to I_SC for PIN photodiodes.

9.2 Why is a series resistor mandatory?

A photodiode, when illuminated, acts essentially as a current source. If connected directly to a voltage source without a series resistor, there is no mechanism to limit the current, leading to excessive power dissipation and instant failure.

9.3 How do I select the operating reverse voltage?

For photoconductive mode, a reverse voltage between 5V and a value safely below the 32V maximum rating can be used. Higher reverse bias reduces capacitance further (increasing speed) but also increases dark current slightly. A common operating point is 5V or 12V.

10. Design and Usage Case Study

Case: Object Counting on a Conveyor Belt

An infrared LED (940nm) is placed on one side of the conveyor, and the PD15-21B/TR8 photodiode is placed directly opposite. Objects passing between them interrupt the infrared beam. The photodiode is operated in photoconductive mode with a 5V reverse bias supplied through a 10kΩ series resistor for protection. The voltage drop across a load resistor (or the output of a transimpedance amplifier connected to the photodiode) is monitored by a microcontroller. A sudden drop in this voltage indicates an object's presence, triggering a count. The fast response time of the photodiode allows for accurate counting of objects moving at high speed. The small 1206 package facilitates integration into a compact sensor head.

11. Operating Principle

A PIN photodiode is a semiconductor device with a wide, lightly doped intrinsic (I) region sandwiched between P-type and N-type regions. When photons with energy greater than the semiconductor's bandgap strike the device, they create electron-hole pairs in the intrinsic region. Under the influence of the built-in electric field (or an externally applied reverse bias), these charge carriers are swept apart, generating a photocurrent that is proportional to the incident light intensity. The intrinsic region reduces the junction capacitance, enabling faster response times compared to standard PN photodiodes.

12. Industry Trends

The trend in optoelectronics continues toward further miniaturization, higher integration, and improved performance. There is growing demand for sensors in consumer electronics (smartphones, wearables), automotive (LiDAR, driver monitoring), and industrial IoT. Photodiodes like the PD15-21B/TR8, which offer a balance of performance, size, and cost, are well-positioned for these markets. Future developments may include integrated photodiodes with on-chip amplification and digital interfaces, as well as devices sensitive to specific wavelengths for spectral analysis applications.

Disclaimer: The information provided in this document is for technical reference. Designers should verify all parameters and ensure their application operates within the specified absolute maximum ratings. Performance can vary with operating conditions.