4.8mm Semi-Lens Silicon PIN Photodiode PD438B Datasheet - 4.8mm Diameter - Black Lens - English Technical Document

1. Product Overview

The PD438B 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 its epoxy package, which is formulated to act as an integrated infrared (IR) filter. This built-in filter is spectrally matched to common IR emitters, enhancing signal-to-noise ratio by selectively passing the target IR wavelength while attenuating unwanted visible light.

The core advantages of the PD438B include its fast response times, high photosensitivity, and small junction capacitance, making it suitable for high-speed detection circuits. The device is constructed using lead-free (Pb-free) materials and complies with relevant environmental regulations such as RoHS and EU REACH, ensuring its suitability for modern electronic manufacturing.

The primary target markets and applications for this photodiode are in consumer electronics and industrial sensing. It is ideally suited for use as a high-speed photo detector in systems like cameras, VCRs, and video cameras. Its characteristics also make it a reliable component in various optoelectronic switches and sensing modules where precise detection of IR signals is critical.

2. In-Depth Technical Parameter Analysis

2.1 Absolute Maximum Ratings

The device is designed to operate reliably within specified environmental and electrical limits. Exceeding these Absolute Maximum Ratings may cause permanent damage.

• Reverse Voltage (VR): 32 V. This is the maximum voltage that can be applied in reverse bias across the photodiode terminals.
• Power Dissipation (Pd): 150 mW. This rating considers the total power the device can handle, primarily from the reverse leakage current under bias.
• Operating Temperature (Topr): -40°C to +85°C. The guaranteed performance range for the photodiode during normal operation.
• Storage Temperature (Tstg): -40°C to +100°C. The safe temperature range for the device when not powered.
• Soldering Temperature (Tsol): 260°C for a maximum duration of 5 seconds. This defines the reflow soldering profile constraints to prevent package damage.

2.2 Electro-Optical Characteristics

These parameters, measured at a standard temperature of 25°C, define the core photodetection performance of the PD438B.

• Spectral Bandwidth (λ0.5): 400 nm to 1100 nm. This defines the wavelength range where the photodiode's responsivity is at least half of its peak value. It confirms sensitivity from visible blue light into the near-infrared.
• Peak Sensitivity Wavelength (λp): 940 nm (Typical). The photodiode is most sensitive to infrared light at this wavelength, which is standard for many IR LEDs and remote control systems.
• Open-Circuit Voltage (VOC): 0.35 V (Typical) under an irradiance (Ee) of 5 mW/cm² at 940nm. This is the voltage generated by the photodiode in photovoltaic mode (no external bias) under specified light conditions.
• Short-Circuit Current (ISC): 18 µA (Typical) under 1 mW/cm² at 940nm. This is the photocurrent generated when the diode terminals are shorted, representing its maximum current output for a given light level.
• Reverse Light Current (IL): 18 µA (Typical) at VR=5V under 1 mW/cm² at 940nm. This is the photocurrent measured when the diode is reverse-biased, which is the standard operating mode for high-speed and linear response.
• Dark Current (Id): 5 nA (Typical), 30 nA (Max) at VR=10V in complete darkness. This is the small leakage current that flows even when no light is present. A low dark current is crucial for detecting weak light signals.
• Reverse Breakdown Voltage (BVR): 170 V (Typical), 32 V (Min). The voltage at which the reverse current increases sharply. The operating reverse voltage should always be kept well below this value.
• Total Capacitance (Ct): 25 pF (Typical) at VR=3V and 1 MHz. This junction capacitance directly impacts the device's speed; a lower capacitance enables faster response times.
• Rise/Fall Time (tr/tf): 50 ns / 50 ns (Typical) with VR=10V and a load resistor (RL) of 1 kΩ. These parameters specify how quickly the photodiode's output current can change in response to a light pulse, defining its high-speed capability.

Tolerances for key parameters are specified: Luminous Intensity (±10%), Dominant Wavelength (±1nm), and Forward Voltage (±0.1V), ensuring consistency in production batches.

3. Performance Curve Analysis

The datasheet provides several characteristic curves that illustrate how key parameters vary with operating conditions. These are essential for circuit designers.

3.1 Spectral Sensitivity

The spectral response curve shows the relative sensitivity of the photodiode across different wavelengths. It will peak sharply around 940 nm due to the integrated IR-filtering epoxy, with significantly reduced sensitivity in the visible spectrum (400-700 nm). This curve is critical for ensuring the detector is matched to the emitter's wavelength.

3.2 Dark Current vs. Ambient Temperature

This curve typically shows an exponential increase in dark current (Id) as the ambient temperature rises. Designers must account for this increased noise floor in high-temperature applications or when detecting very low-light signals.

3.3 Reverse Light Current vs. Irradiance (Ee)

This graph demonstrates the linear relationship between the incident light power (irradiance) and the generated photocurrent (IL) when the diode is reverse-biased. The linearity is a key feature of PIN photodiodes, making them suitable for light measurement applications.

3.4 Terminal Capacitance vs. Reverse Voltage

The junction capacitance (Ct) decreases as the reverse bias voltage (VR) increases. This curve allows designers to select an operating bias voltage that optimizes the trade-off between speed (lower capacitance at higher voltage) and power consumption/heat.

3.5 Response Time vs. Load Resistance

The rise/fall time (tr/tf) is influenced by the RC time constant formed by the photodiode's junction capacitance and the external load resistance (RL). This curve shows how response time increases with larger load resistors, guiding the selection of RL for desired speed in transimpedance amplifier circuits.

3.6 Power Dissipation vs. Ambient Temperature

This derating curve indicates the maximum allowable power dissipation as a function of the ambient temperature. As temperature increases, the maximum safe power the device can handle decreases linearly, which is vital for thermal management in the system design.

4. Mechanical and Package Information

4.1 Package Dimensions

The PD438B is housed in a cylindrical side-view package with a nominal diameter of 4.8mm. The detailed mechanical drawing in the datasheet provides all critical dimensions including body diameter, length, lead spacing, and lead diameter. A standard tolerance of ±0.25mm applies to all package dimensions unless otherwise specified. The side-view configuration is designed for applications where the light path is parallel to the PCB surface.

4.2 Polarity Identification

The photodiode is a polarized component. The cathode is typically identified by a longer lead, a flat spot on the package, or a specific marking. The datasheet's package diagram clearly indicates the anode and cathode connections, which must be observed during assembly to ensure correct biasing (reverse bias for normal operation).

5. Soldering and Assembly Guidelines

To maintain reliability and prevent damage during the assembly process, specific soldering conditions must be followed.

• Reflow Soldering: The component is suitable for surface-mount assembly using reflow soldering techniques. The peak soldering temperature must not exceed 260°C, and the time above this temperature should be limited to 5 seconds or less to prevent thermal damage to the epoxy package and the semiconductor die.
• Hand Soldering: If hand soldering is necessary, a temperature-controlled soldering iron should be used. Contact time with the leads should be minimized, and heat sinking of the lead between the joint and the package body is recommended.
• Storage Conditions: The devices should be stored in their original moisture-barrier bags in an environment controlled within the storage temperature range of -40°C to +100°C and at low humidity to prevent oxidation of the leads.

6. Packaging and Ordering Information

6.1 Packing Specification

The standard packing flow for the PD438B is as follows: 500 pieces are packaged in one anti-static bag. Six of these bags are then placed into one inner carton. Finally, ten inner cartons are packed into one master shipping (outside) carton, resulting in a total of 30,000 pieces per master carton.

6.2 Label Specification

The label on the packaging contains several key identifiers:

• CPN: Customer's Product Number (if assigned).
• P/N: The manufacturer's product number (PD438B).
• QTY: The quantity of devices in the package.
• CAT, HUE, REF: Codes representing the luminous intensity rank, dominant wavelength rank, and forward voltage rank, respectively, for products that are binned.
• LOT No: The traceable manufacturing lot number.

This labeling ensures traceability and correct material handling throughout the supply chain.

7. Application Notes and Design Considerations

7.1 Typical Application Circuits

The PD438B is most commonly used in one of two circuit configurations:

1. Photovoltaic Mode (Zero Bias): The photodiode is connected directly to a high-impedance load (like an op-amp input). This mode offers minimal dark current and noise but has slower response and lower linearity. It's suitable for low-speed, precision light measurement.
2. Photoconductive Mode (Reverse Bias): The photodiode is connected with the cathode to a positive voltage and the anode to a virtual ground (e.g., the inverting input of a transimpedance amplifier). This is the recommended mode for the PD438B to leverage its high-speed capabilities. Reverse bias reduces junction capacitance (increasing speed) and improves linearity. The value of the feedback resistor in the transimpedance amplifier sets the gain (Vout = Iphoto * Rfeedback).

7.2 Design Considerations

• Bias Voltage Selection: Choose a reverse bias voltage (e.g., 5V to 10V) that provides a good compromise between speed (lower capacitance) and power consumption. Do not exceed the maximum reverse voltage of 32V.
• Amplifier Selection: For high-speed applications, pair the PD438B with a low-noise, high-bandwidth operational amplifier configured as a transimpedance amplifier. The amplifier's input bias current and voltage noise should be low to not degrade the photodiode's signal.
• PCB Layout: Keep the photodiode and its associated amplifier close together to minimize parasitic capacitance and noise pickup on the sensitive high-impedance node. Use a guard ring connected to a low-impedance point (like the amplifier's output or a ground plane) around the photodiode's anode connection to reduce leakage currents.
• Optical Alignment: Ensure proper mechanical alignment between the IR emitter and the photodiode. The side-view package is designed for this. Consider using a tube or barrier to block ambient light and crosstalk.

8. Technical Comparison and Differentiation

The PD438B differentiates itself in the market through several key features:

• Integrated IR Filter: The epoxy package itself acts as the filter, eliminating the need for a separate filter component, reducing part count, cost, and simplifying assembly.
• Side-View Package: The cylindrical side-view form factor is ideal for applications where the light path runs parallel to the PCB, such as in slot sensors, edge-sensing systems, and certain types of encoders.
• Balanced Performance: It offers a well-balanced combination of speed (50 ns), sensitivity (18 µA at 1 mW/cm²), and low dark current, making it a versatile choice for a wide range of medium-to-high-speed IR detection tasks.
• Environmental Compliance: Its Pb-free construction and compliance with RoHS and REACH make it suitable for global markets with strict environmental regulations.

Compared to larger photodiodes, it offers a smaller footprint. Compared to unfiltered photodiodes, it provides superior rejection of ambient visible light noise.

9. Frequently Asked Questions (FAQ)

Q1: What is the purpose of the black epoxy lens?
A1: The black epoxy is not just for appearance; it is formulated to be an effective infrared filter. It transmits the target IR wavelength (peaking at 940 nm) while absorbing much of the visible light, significantly reducing interference from ambient light sources like room lighting.

Q2: Should I operate the PD438B with or without a reverse bias voltage?
A2: For high-speed operation (as indicated by its 50 ns rise time), it is strongly recommended to operate the PD438B in photoconductive mode with a reverse bias, typically between 5V and 10V. This reduces junction capacitance and improves linearity and speed.

Q3: How do I convert the photocurrent into a usable voltage signal?
A3: The most common and effective method is to use a transimpedance amplifier (TIA) circuit. The photodiode connects between the inverting input and the output of an op-amp, with a feedback resistor determining the gain (Vout = -Iphoto * Rf). A small feedback capacitor is often added in parallel with the resistor to stabilize the circuit and limit bandwidth.

Q4: What is the significance of the "Dark Current" parameter?
A4: Dark current is the small current that flows through the photodiode when it is in complete darkness and under reverse bias. It acts as a noise source. A lower dark current (5 nA typical for the PD438B) means the device can detect weaker light signals without the signal being masked by its own noise.

Q5: Can this photodiode be used for visible light detection?
A5: While its spectral range starts at 400 nm (violet), its sensitivity in the visible spectrum is greatly attenuated by the IR-filtering epoxy lens. Its peak sensitivity is firmly in the infrared at 940 nm. For primary visible light detection, a photodiode without an IR-filtering package would be more appropriate.

10. Operational Principles

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 strike the device, they create electron-hole pairs in the intrinsic region. Under the influence of an external reverse bias electric field, these charge carriers are swept apart, generating a photocurrent that is proportional to the incident light intensity. The wide intrinsic region allows for several advantages: it creates a larger depletion region for photon absorption (increasing sensitivity), reduces junction capacitance (increasing speed), and allows operation at higher reverse voltages. The PD438B utilizes silicon, which has a bandgap suitable for detecting light from the visible to the near-infrared spectrum.

11. Disclaimer and Usage Notes

The information contained in this technical document is subject to change without notice. The graphs and typical values provided are for design guidance and do not represent guaranteed specifications. When implementing this component, designers must strictly adhere to the Absolute Maximum Ratings to prevent device failure. The manufacturer assumes no liability for any damage resulting from the use of this product outside its specified operating conditions. This product is not intended for use in safety-critical, life-supporting, military, automotive, or aerospace applications without prior consultation and specific qualification.