4.8mm Semi-Lens Silicon PIN Photodiode PD438C/S46 Datasheet - 4.8mm Diameter - 32V Reverse Voltage - 940nm Peak Sensitivity - English Technical Document

1. Product Overview

The PD438C/S46 is a high-performance silicon PIN photodiode designed for applications requiring fast response and high sensitivity to infrared light. It is housed in a compact, cylindrical side-view plastic package with a diameter of 4.8mm. A key feature of this device is that the epoxy package itself acts as an integrated infrared (IR) filter, which is spectrally matched to common IR emitters, enhancing its performance in IR detection systems by filtering out unwanted visible light.

This photodiode is characterized by its fast response times, high photosensitivity, and small junction capacitance, making it suitable for high-speed optical detection. It is constructed using lead-free materials and complies with relevant environmental regulations.

2. Technical Parameter Deep Dive

2.1 Absolute Maximum Ratings

The device is designed to operate reliably within specified limits. Exceeding these ratings may cause permanent damage.

• Reverse Voltage (V_R): 32 V - The maximum voltage that can be applied in reverse bias across the photodiode terminals.
• Power Dissipation (P_d): 150 mW - The maximum power the device can dissipate, primarily as heat, under specified conditions.
• Operating Temperature (T_opr): -40°C to +85°C - The ambient temperature range over which the device is guaranteed to meet its published specifications.
• Storage Temperature (T_stg): -40°C to +100°C - The temperature range for safe storage when the device is not powered.
• Soldering Temperature (T_sol): 260°C for a duration not exceeding 5 seconds, which is typical for lead-free reflow soldering processes.

2.2 Electro-Optical Characteristics

These parameters are measured at an ambient temperature (T_a) of 25°C and define the core performance of the photodiode.

• Spectral Bandwidth (λ_0.5): 840 nm to 1100 nm. This defines the range of wavelengths where the photodiode's responsivity is at least half of its peak value. It is sensitive primarily in the near-infrared region.
• Peak Sensitivity Wavelength (λ_p): 940 nm (Typical). The wavelength of light at which the photodiode is most sensitive. This matches the common emission wavelength of many IR LEDs.
• Open-Circuit Voltage (V_OC): 0.35 V (Typical) when illuminated with an irradiance (E_e) of 5 mW/cm² at 940nm. This is the voltage generated by the photodiode with no external load.
• Short-Circuit Current (I_SC): 18 µA (Typical) at E_e = 1 mW/cm², λ_p=940nm. This is the photocurrent when the output is shorted.
• Reverse Light Current (I_L): 18 µA (Typical, Min 10.2 µA) at E_e = 1 mW/cm², λ_p=940nm, and a reverse bias voltage (V_R) of 5V. This is the primary operating parameter in photoconductive mode.
• Dark Current (I_d): 5 nA (Typical, Max 30 nA) at V_R = 10V in complete darkness. This is the small leakage current that flows even when no light is present, a key parameter for signal-to-noise ratio.
• Reverse Breakdown Voltage (BV_R): Min 32V, Typ 170V, measured at a reverse current of 100 µA. This indicates the voltage at which the junction breaks down.
• Total Capacitance (C_t): 18 pF (Typical) at V_R = 3V and a test frequency of 1 MHz. Lower capacitance enables faster response times.
• Rise/Fall Time (t_r/t_f): 50 ns / 50 ns (Typical) with V_R = 10V and a load resistance (R_L) of 1 kΩ. This specifies the speed of the photodiode's response to a light pulse.

Tolerances for key parameters are specified as: Luminous Intensity ±10%, Dominant Wavelength ±1nm, Forward Voltage ±0.1V.

3. Performance Curve Analysis

The datasheet provides several characteristic curves that illustrate performance under varying conditions. These are essential for design engineers.

3.1 Spectral Sensitivity

A curve plotting relative sensitivity against wavelength. It confirms the peak sensitivity at approximately 940nm and shows the spectral response rolling off towards the boundaries of the 840-1100nm range. The integrated epoxy lens acts as a filter, attenuating response outside the target IR band.

3.2 Dark Current vs. Ambient Temperature

This curve typically shows that dark current (I_d) increases exponentially with rising temperature. Understanding this relationship is critical for applications operating over a wide temperature range, as it defines the lower limit of detectable light (noise floor).

3.3 Reverse Light Current vs. Irradiance (E_e)

This graph demonstrates the linear relationship between the generated photocurrent (I_L) and the incident light power density. The photodiode operates in a highly linear region under the specified conditions, which is vital for analog light measurement applications.

3.4 Terminal Capacitance vs. Reverse Voltage

The junction capacitance (C_t) decreases with increasing reverse bias voltage. This is a fundamental property of PN junctions. Designers can use a higher bias voltage to reduce capacitance and thus improve bandwidth and response speed, at the trade-off of slightly increased dark current.

3.5 Response Time vs. Load Resistance

This curve shows how the rise/fall time is affected by the value of the external load resistor (R_L). A smaller R_L generally results in faster response but produces a smaller output voltage swing. This graph helps optimize the speed-amplitude trade-off in the circuit design.

3.6 Power Dissipation vs. Ambient Temperature

Illustrates the derating of the maximum allowable power dissipation as the ambient temperature increases. At temperatures above 25°C, the device cannot dissipate the full 150mW, and the maximum power must be reduced linearly to zero at the maximum junction temperature.

4. Mechanical and Package Information

4.1 Package Dimension

The PD438C/S46 is packaged in a cylindrical side-view plastic package with a nominal diameter of 4.8mm. The dimensional drawing specifies the body diameter, length, lead spacing, and lead diameter. A critical note specifies that all dimensional tolerances are ±0.25mm unless otherwise stated on the drawing. The side-view configuration is ideal for applications where the light path is parallel to the PCB surface.

4.2 Polarity Identification

Polarity is typically indicated on the package or in the drawing. For a photodiode, the cathode is usually connected to the positive supply voltage when operated in reverse bias (photoconductive mode), and the anode is connected to the circuit ground or the input of a transimpedance amplifier. Correct polarity is essential for proper operation.

5. Soldering and Assembly Guidelines

The device is suitable for standard surface-mount assembly processes.

• Reflow Soldering: The maximum recommended soldering temperature is 260°C. The time that the device leads are exposed to temperatures at or above this peak should not exceed 5 seconds. This is consistent with typical lead-free reflow profiles (e.g., IPC/JEDEC J-STD-020).
• Hand Soldering: If hand soldering is necessary, a temperature-controlled iron should be used. Contact time per lead should be minimized to prevent excessive heat transfer to the sensitive semiconductor die.
• Cleaning: Standard PCB cleaning processes can be used, but compatibility of cleaning agents with the plastic package material should be verified.
• Storage Conditions: Devices should be stored in their original moisture-barrier bags at temperatures between -40°C and +100°C and at low humidity to prevent oxidation of the leads and moisture absorption by the package.

6. Packaging and Ordering Information

6.1 Packing Specification

The standard packing flow is as follows: 500 pieces are packed in one bag. Five bags are then placed into one inner carton. Finally, ten inner cartons are packed into one master (outside) carton. This results in a total of 25,000 pieces per master carton.

6.2 Label Specification

Labels on the packaging contain key information for traceability and identification:

• CPN: Customer's Product Number (if assigned).
• P/N: Manufacturer's Product Number (e.g., PD438C/S46).
• QTY: Quantity of devices in the package.
• CAT, HUE, REF: Codes for luminous intensity rank, dominant wavelength rank, and forward voltage rank, respectively, indicating performance binning.
• LOT No: Manufacturing lot number for traceability.
• REF: A reference number to identify the label.

7. Application Suggestions

7.1 Typical Application Scenarios

• High-Speed Photo Detector: Ideal for optical data links, encoders, and pulse detection where the 50ns response time is a key advantage.
• Camera Applications: Can be used in autofocus systems, light metering, or as an IR presence detector.
• Optoelectronic Switch: Used in object detection, slot sensors, and limit switches. The integrated IR filter helps reject ambient light interference.
• VCRs and Video Cameras: Historically used in tape counter sensors, remote control receivers, or other internal optical sensing functions.

7.2 Design Considerations

• Bias Voltage: Operating in photoconductive mode (with reverse bias) is recommended for high-speed and linear operation. A bias of 5V to 10V is typical, balancing speed (lower capacitance) and noise (lower dark current).
• Circuit Topology: For best speed and linearity, use a transimpedance amplifier (TIA) to convert the photocurrent into a voltage. The feedback resistor and capacitor in the TIA must be chosen based on the desired bandwidth and the photodiode's capacitance.
• Optical Alignment: The side-view package requires careful mechanical design to ensure proper alignment with the light source, which is often also a side-view IR LED.
• Ambient Light Rejection: While the epoxy acts as an IR filter, for environments with strong IR sources (e.g., sunlight), additional optical filtering or modulation/demodulation techniques may be necessary.

8. Technical Comparison and Differentiation

The PD438C/S46 offers several distinct advantages in its class:

• Integrated IR Filter: Unlike many basic photodiodes that require a separate filter, the package epoxy is formulated to filter light, simplifying assembly and reducing component count.
• Side-View Package: The 4.8mm cylindrical side-view package is a specific form factor optimized for applications where the light path runs parallel to the PCB, offering a compact and directed field of view.
• Balanced Performance: It provides a good balance between speed (50ns), sensitivity (18 µA at 1 mW/cm²), and dark current (5 nA), making it a versatile choice for general-purpose IR detection.
• Robust Ratings: With a reverse voltage rating of 32V and a wide operating temperature range (-40°C to +85°C), it is suitable for industrial and automotive environments (for non-safety critical applications as per disclaimer).

9. Frequently Asked Questions (Based on Technical Parameters)

Q: What is the difference between operating in photovoltaic (zero bias) and photoconductive (reverse bias) mode?
A: In photovoltaic mode (V_R=0V), the photodiode generates its own voltage (see V_OC). It has very low dark current but higher capacitance and slower response. Photoconductive mode (applying V_R) widens the depletion region, lowering capacitance and speeding up response (see t_r/t_f), at the cost of a small, constant dark current (I_d). For high-speed detection, photoconductive mode is preferred.

Q: How do I interpret the "Reverse Light Current (I_L)" parameter?
A: This is the most useful parameter for circuit design. It tells you that under a specific light condition (1 mW/cm² at 940nm) and with a 5V reverse bias, you can expect a photocurrent of typically 18 µA. Your amplifier circuit must be designed to handle this current range. The minimum value of 10.2 µA is important for worst-case design.

Q: Why is the dark current important?
A: Dark current is the primary source of noise in a photodiode when no light is present. It sets the lower limit of detectable light. A lower dark current (5 nA typical for this device) means the sensor can detect fainter light signals. Note that dark current doubles approximately every 10°C increase in temperature.

Q: Can I use this with light sources other than 940nm?
A: Yes, but with reduced sensitivity. Refer to the Spectral Sensitivity curve. The photodiode will respond to light from about 840nm to 1100nm, but the output current for the same optical power will be lower if the wavelength is not near the 940nm peak.

10. Practical Design and Usage Case

Case: Designing an IR Proximity Sensor for an Automatic Faucet.

1. System Block: An IR LED (emitting at 940nm) and the PD438C/S46 photodiode are placed side-by-side behind a translucent window. The LED is pulsed. When no object is present, most IR light disperses. When a hand is placed near the faucet, reflected IR light enters the photodiode.
2. Component Selection Rationale: The PD438C/S46 is chosen because its 940nm peak sensitivity matches the LED. The integrated IR filter in its package helps reject ambient visible light from overhead lamps, reducing false triggers. The side-view package allows both emitter and detector to be mounted flat on the PCB, pointing outwards.
3. Circuit Design: The photodiode is reverse-biased with 5V. Its output is connected to a transimpedance amplifier. The amplifier's gain (feedback resistor) is set so that the expected reflected signal (a fraction of the 18 µA/mW/cm²) produces a usable voltage. A comparator after the amplifier detects when this voltage exceeds a set threshold.
4. Optimization: The LED pulse frequency and duration are chosen to be outside the frequency of ambient light flicker (e.g., 100Hz from mains lighting). The system only looks for the signal synchronized with the LED pulse, providing excellent noise immunity.

11. Operating Principle Introduction

A PIN photodiode is a semiconductor device with a wide, lightly doped intrinsic (I) region sandwiched between a P-type and an N-type region. When photons with energy greater than the semiconductor's bandgap (for silicon, wavelengths shorter than ~1100nm) strike the device, they can create electron-hole pairs in the intrinsic region. Under the influence of the built-in electric field (in photovoltaic mode) or an applied reverse bias field (in photoconductive mode), these charge carriers are swept apart, generating a photocurrent that is proportional to the incident light intensity. The wide intrinsic region in a PIN structure reduces junction capacitance (enabling faster response) and increases the volume for photon absorption (improving sensitivity), compared to a standard PN photodiode.

12. Technology Trends and Context

Silicon PIN photodiodes like the PD438C/S46 are mature, reliable, and cost-effective solutions for near-infrared detection. Current trends in the field include:

• Integration: Moving towards integrated solutions that combine the photodiode, amplifier, and sometimes even the LED driver and digital logic into a single package or chip (e.g., opto-ASICs).
• Miniaturization: Development of photodiodes in smaller surface-mount packages (e.g., chip-scale packages) for space-constrained applications like mobile devices.
• Specialized Materials: For wavelengths beyond silicon's cutoff (~1100nm), materials like InGaAs are used. However, silicon remains dominant for the visible and near-IR spectrum due to its low cost and excellent manufacturability.
• Enhanced Performance: Ongoing research focuses on reducing capacitance and dark current further to improve speed and sensitivity, often through advanced doping profiles and device structures.

The PD438C/S46 represents a well-optimized, application-specific component within this broader technological landscape, offering a practical balance of performance, size, and cost for a wide range of industrial and consumer IR sensing tasks.