PD638B Silicon PIN Photodiode Datasheet - 2.75x5.25mm - 32V Reverse Voltage - 150mW Power Dissipation - Black Lens - English Technical Document

1. Product Overview

The PD638B is a high-speed, highly sensitive Silicon PIN photodiode housed in a compact flat side-view plastic package measuring 2.75mm by 5.25mm. This component is specifically designed for applications requiring fast optical detection. Its epoxy package is formulated to act as an integrated infrared (IR) filter, with its spectral characteristics carefully matched to common IR emitters, enhancing signal-to-noise ratio in IR sensing systems. The device is compliant with RoHS and EU REACH regulations and is constructed using lead-free materials.

1.1 Core Advantages and Target Market

The primary advantages of the PD638B include its exceptionally fast response times, high photosensitivity, and small junction capacitance, which are critical for high-bandwidth applications. Its small form factor makes it suitable for space-constrained designs. The integrated IR-filtering package simplifies optical design by reducing the need for external filters. This photodiode is targeted at markets and applications involving high-speed optical detection, imaging systems, and optoelectronic switching, such as in consumer electronics, industrial automation, and communication devices.

2. In-Depth Technical Parameter Analysis

This section provides a detailed, objective interpretation of the key technical parameters specified in the datasheet, explaining their significance for design engineers.

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. Operation under or at these limits is not guaranteed.

• Reverse Voltage (VR): 32 V. This is the maximum reverse bias voltage that can be applied across the photodiode terminals. Exceeding this voltage risks avalanche breakdown and device failure.
• Power Dissipation (Pd): 150 mW. This is the maximum allowable power the device can dissipate as heat, primarily determined by the product of the reverse voltage and the dark current or photocurrent under operating conditions.
• Operating Temperature (Topr): -40°C to +85°C. The ambient temperature range over which the device is specified to operate correctly.
• Storage Temperature (Tstg): -40°C to +100°C. The temperature range for non-operational storage without degradation.
• Soldering Temperature (Tsol): 260°C for a duration not exceeding 5 seconds. This is critical for PCB assembly using reflow or hand-soldering processes to prevent package damage.

2.2 Electro-Optical Characteristics

These parameters, measured at Ta=25°C, define the core performance of the photodiode as a light sensor.

• Spectral Bandwidth (λ0.5): 840 nm to 1100 nm. This range indicates the wavelengths at which the photodiode's responsivity is at least half of its peak value. It confirms the device is optimized for the near-infrared spectrum.
• Peak Sensitivity Wavelength (λp): 940 nm (Typical). The photodiode is most sensitive to light at this infrared wavelength, making it ideal for pairing with 940nm IR LEDs.
• Open-Circuit Voltage (VOC): 0.35 V (Typical) at Ee=5 mW/cm², λp=940nm. This is the voltage generated by the photodiode in photovoltaic mode (zero bias) under the specified illumination.
• Short-Circuit Current (ISC): 18 µA (Typical) at Ee=1 mW/cm², λp=940nm. This is the photocurrent generated when the diode terminals are shorted (zero voltage across it).
• Reverse Light Current (IL): 18 µA (Typical, Min 10.2 µA) at Ee=1 mW/cm², λp=940nm, VR=5V. This is a key parameter for photoconductive mode operation (applied reverse bias). It defines the signal current for a given light intensity.
• Dark Current (Id): 5 nA (Typical, Max 30 nA) at VR=10V. This is the small reverse leakage current that flows when the device is in complete darkness. Lower dark current is better for detecting weak light signals.
• Reverse Breakdown Voltage (BVR): 170 V (Typical, Min 32 V) measured at IR=100µA. This is the voltage at which the reverse current increases sharply. The operating reverse voltage should be well below this value.
• Total Capacitance (Ct): 25 pF (Typical) at VR=3V, f=1 MHz. Junction capacitance is a critical factor limiting bandwidth. A lower capacitance allows for faster response times.
• Rise/Fall Time (tr/tf): 50 ns / 50 ns (Typical) at VR=10V, RL=1 kΩ. This specifies the speed of the current output in response to a step change in light intensity. The 50 ns value indicates suitability for medium to high-speed detection applications.

3. Binning System Explanation

The PD638B is available in different performance bins, primarily based on the Reverse Light Current (IL) parameter measured under standard conditions (Ee=1 mW/cm², λp=940nm, VR=5V). This allows designers to select a device with a guaranteed photocurrent range for consistent system performance.

• BIN1: IL = 10.2 µA (Min) to 16.5 µA (Max)
• BIN2: IL = 13.5 µA (Min) to 22.0 µA (Max)
• BIN3: IL = 18.0 µA (Min) to 27.5 µA (Max)
• BIN4: IL = 22.5 µA (Min) to 33.0 µA (Max)

The datasheet also notes standard tolerances for related parameters: Luminous Intensity (±10%), Dominant Wavelength (±1nm), and Forward Voltage (±0.1V), though these are more typical for emitters and may be listed for reference in related products.

4. Performance Curve Analysis

The typical characteristic curves provide visual insight into how key parameters vary with operating conditions.

4.1 Power Dissipation vs. Ambient Temperature

This curve shows the derating of the maximum allowable power dissipation as the ambient temperature rises above 25°C. To ensure reliability, the dissipated power must be reduced linearly according to this graph when operating at higher temperatures.

4.2 Spectral Sensitivity

This plot illustrates the normalized responsivity of the photodiode across the wavelength spectrum. It visually confirms the peak at 940 nm and the defined spectral bandwidth from 840 nm to 1100 nm, showing the integrated IR filter's effect in attenuating visible light.

4.3 Dark Current vs. Ambient Temperature

Dark current is highly temperature-dependent, typically doubling for every 10°C rise in temperature. This curve allows designers to estimate the noise floor (dark current) at their specific operating temperature, which is crucial for low-light or high-gain applications.

4.4 Reverse Light Current vs. Irradiance (Ee)

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

4.5 Terminal Capacitance vs. Reverse Voltage

Junction capacitance decreases with increasing reverse bias voltage. This curve shows how applying a higher reverse voltage (within limits) can reduce Ct, thereby potentially improving the response speed of the circuit.

4.6 Response Time vs. Load Resistance

The rise/fall time is affected by the RC time constant formed by the photodiode's junction capacitance and the external load resistance (RL). This curve guides the selection of RL to achieve the desired bandwidth, showing that smaller RL values yield faster response but smaller output voltage swings.

5. Mechanical and Package Information

5.1 Package Dimensions

The PD638B comes in a flat side-view plastic package. The key dimensions from the drawing are a body size of 2.75mm (width) x 5.25mm (length). The lead spacing and overall height are also defined. All unspecified tolerances are ±0.25mm unless otherwise noted on the dimensioned drawing. The package features a black lens which serves as the integrated IR filter.

5.2 Polarity Identification

The cathode (K) and anode (A) terminals must be correctly identified for proper circuit connection. The datasheet's package diagram indicates the pinout. Typically, the cathode is connected to the more positive voltage in reverse-bias (photoconductive) operation.

6. Soldering and Assembly Guidelines

The absolute maximum rating for soldering is 260°C for a duration not exceeding 5 seconds. This is compatible with standard lead-free reflow soldering profiles (IPC/JEDEC J-STD-020). It is critical to adhere to this limit to prevent thermal damage to the epoxy package, internal die attach, or wire bonds. For hand soldering, a temperature-controlled iron should be used with minimal contact time. Standard ESD (Electrostatic Discharge) precautions should be observed during handling and assembly, as photodiodes are sensitive semiconductor devices.

7. Packaging and Ordering Information

7.1 Packing Specification

The standard packing configuration is:
1. 500 pieces per anti-static bag.
2. 6 bags per inner carton.
3. 10 inner cartons per master (outside) carton.
This results in a total of 30,000 pieces per master carton.

7.2 Label Specification

The label on the packaging contains several fields for traceability and identification:
CPN: Customer's Part Number.
P/N: Manufacturer's Product Number (e.g., PD638B).
QTY: Quantity packed.
CAT: Luminous Intensity Rank (BIN code).
HUE: Dominant Wavelength Rank.
REF: Forward Voltage Rank.
LOT No: Manufacturing Lot Number for traceability.
X: Month code.
A reference number identifies the label itself.

8. Application Suggestions

8.1 Typical Application Scenarios

• High-Speed Photo Detector: In optical communication links, barcode scanners, or pulse detection systems where the 50 ns response time is utilized.
• Camera: Likely for use in IR-cut filter detection, light meter sensors, or proximity sensing in camera modules.
• Optoelectronic Switch: In object detection, position sensing, or interruptor modules where an IR beam is broken.
• VCRs, Video Camera: For tape-end detection, auto-focus assist systems, or remote control receiver circuits (though dedicated IR receiver modules are more common for RC).

8.2 Design Considerations

• Bias Selection: Decide between photovoltaic (zero bias, low noise) and photoconductive (reverse bias, faster speed, linearity) mode based on application needs for speed, noise, and output linearity.
• Biasing Circuit: For photoconductive mode, ensure a stable reverse bias supply. A simple resistor from a voltage source is common, but an op-amp based transimpedance amplifier (TIA) is standard for converting photocurrent to voltage with high gain and bandwidth.
• Bandwidth vs. Sensitivity: There is a trade-off. Using a larger load resistor (RL) in a simple circuit increases output voltage but reduces bandwidth due to higher RC constant. A TIA configuration offers better control over this trade-off.
• Optical Alignment: Ensure proper mechanical alignment between the IR source (e.g., 940nm LED) and the photodiode's active area, considering its side-view package orientation.
• Ambient Light Rejection: While the built-in IR filter helps, additional optical shielding or modulation/demodulation techniques may be necessary in environments with strong ambient IR light (e.g., sunlight).

9. Technical Comparison and Differentiation

Compared to standard PN photodiodes, the PIN structure of the PD638B offers distinct advantages:
Wider Depletion Region: The intrinsic (I) region creates a larger depletion width under reverse bias. This leads to:
1. Lower Junction Capacitance: Enabling faster response times (50 ns vs. typically microseconds for some PN diodes).
2. Higher Quantum Efficiency: The wider region allows more photons to be absorbed within the depletion zone, generating more carriers per photon and resulting in higher photosensitivity.
3. Improved Linearity: The electric field is more uniform across the I-region, leading to better linearity between light intensity and photocurrent over a wide range.
The integrated IR filter is another key differentiator, reducing component count and simplifying optical assembly compared to using a separate photodiode and filter.

10. Frequently Asked Questions (Based on Technical Parameters)

10.1 What is the difference between Short-Circuit Current (ISC) and Reverse Light Current (IL)?

ISC is measured with zero volts across the diode (short circuit). IL is measured with a specified reverse bias applied (e.g., 5V). In an ideal photodiode, they would be equal, but in practice, IL might be slightly higher due to the electric field sweeping carriers more efficiently. The datasheet lists both; IL is more relevant for typical reverse-biased operation.

10.2 How do I choose the right BIN?

Select the BIN based on the required minimum signal current for your circuit to function reliably. If your system gain is fixed, choose a BIN that guarantees your needed photocurrent at the expected light level. BIN3 (18-27.5 µA) provides the typical value. For tighter system-to-system consistency, specify a single BIN.

10.3 Can I operate this photodiode at voltages between 5V and 32V?

Yes, you can operate it at any reverse voltage up to the Absolute Maximum Rating of 32V. Operating at a higher reverse bias (e.g., 10V or 20V) will generally reduce junction capacitance (improving speed) and may slightly increase photocurrent, but it will also increase dark current. The electro-optical characteristics table provides specific data at VR=5V and VR=10V for reference.

10.4 Is an external amplifier necessary?

For most applications, yes. The output photocurrent is in the microamp range. A transimpedance amplifier (TIA) is the standard circuit to convert this small current into a usable voltage signal with controllable gain and bandwidth. A simple resistor load can be used for very basic, low-speed switching applications.

11. Practical Design and Usage Example

Scenario: Designing a High-Speed Optical Interrupter Switch.
Goal: Detect the presence of an object breaking an IR beam with a response time faster than 100 µs.
Design Steps:
1. Pairing: Use a 940nm IR LED as the light source, driven with a pulsed current to save power and reject ambient light.
2. Biasing: Operate the PD638B in photoconductive mode. Apply a reverse bias of 5V to 10V through a current-limiting resistor from the supply rail.
3. Signal Conditioning: Connect the photodiode anode to the inverting input of an op-amp configured as a TIA. The cathode is connected to the bias supply. The feedback resistor (Rf) of the TIA sets the gain (Vout = I_photo * Rf). A feedback capacitor (Cf) in parallel with Rf is used to control bandwidth and stability.
4. Component Selection: Choose an op-amp with sufficient gain-bandwidth product, low input bias current, and low noise. Select Rf to get a suitable output voltage swing when the beam is unbroken. Calculate Cf based on the photodiode capacitance (Ct ~25pF) and desired bandwidth: f_3dB ≈ 1/(2π * Rf * Ct) for the basic RC limit, but op-amp stability calculations are crucial.
5. Output Processing: The TIA output is a voltage that drops when the beam is interrupted. This signal can be fed into a comparator with hysteresis to create a clean digital output signal.

12. Operating Principle Introduction

A PIN photodiode is a semiconductor device with a structure of P-type, Intrinsic (undoped), and N-type layers. In the photoconductive mode of operation, a reverse bias voltage is applied. This widens the depletion region, which primarily encompasses the intrinsic layer. When photons with energy greater than the semiconductor's bandgap (e.g., infrared light for silicon) strike the depletion region, they excite electrons from the valence band to the conduction band, creating electron-hole pairs. The strong electric field present in the depletion region due to the reverse bias swiftly separates these carriers and sweeps them towards the respective terminals—electrons to the N-side and holes to the P-side. This movement of charge constitutes a photocurrent that flows in the external circuit, proportional to the intensity of the incident light. The intrinsic layer's key role is to provide a large, low-field region for photon absorption and carrier generation, leading to high efficiency and speed while keeping capacitance low.

13. Technology Trends and Developments

The field of photodetection continues to evolve. General trends relevant to components like the PD638B include:
Increased Integration: Moving towards photodiodes integrated with amplification and signal conditioning circuits on a single chip (e.g., integrated photodiode-amplifier combinations).
Enhanced Performance: Ongoing development aims for even lower dark currents, higher speeds (sub-nanosecond response), and improved sensitivity across broader spectral ranges.
Advanced Packaging: Development of wafer-level chip-scale packaging (WLCSP) for even smaller footprints and better high-frequency performance, as well as packages with integrated lenses for improved light collection.
New Materials: Exploration of materials like InGaAs for extended infrared range detection beyond silicon's limit (~1100 nm). However, silicon PIN photodiodes like the PD638B remain the dominant, cost-effective solution for the near-IR spectrum due to silicon's mature fabrication technology and excellent performance-to-cost ratio.

14. Disclaimer and Usage Notes

Critical disclaimers and usage notes are provided, which must be adhered to:
1. The manufacturer reserves the right to adjust product material specifications.
2. Products meet published specifications for 12 months from the shipment date.
3. Graphs and typical values are for reference only and do not represent guaranteed minimum or maximum limits.
4. The user is responsible for operating the device within the Absolute Maximum Ratings. The manufacturer assumes no liability for damage resulting from operation outside these ratings or misuse.
5. The datasheet content is copyrighted; reproduction requires prior consent.
6. This product is not intended for use in safety-critical, military, aerospace, automotive, medical, life-support, or life-saving applications. For such applications, contact the manufacturer for qualified components.