LTR-X130P Optical Sensor Datasheet - Integrated Proximity & Ambient Light Sensor - I2C Interface - 1.7V to 3.6V - English Technical Document

1. Product Overview

The LTR-X130P is a highly integrated, low-voltage optical sensor combining proximity sensing (PS) and ambient light sensing (ALS) functionalities within a single, miniature, lead-free surface-mount ChipLED package. Its core design philosophy centers on enabling sophisticated object detection and light measurement in space-constrained, battery-powered applications.

The sensor's primary advantage lies in its system-level integration. It features a built-in infrared emitter (LED), visible and infrared photodiodes, analog-to-digital converters (ADCs), a programmable interrupt controller, and a full I2C digital interface. This integration significantly reduces external component count and simplifies PCB layout. A key performance feature is its excellent ambient light suppression, capable of operating accurately under direct sunlight conditions up to 100,000 lux, making it suitable for outdoor or brightly lit indoor environments. The programmable interrupt function allows the host microcontroller to enter low-power sleep modes, waking only when specific proximity thresholds are crossed, thereby optimizing overall system power efficiency—a critical factor for mobile and portable devices.

The target market encompasses a wide range of consumer electronics and computing devices. Its primary applications include automatic display backlight dimming and brightness control in smartphones, tablets, laptops, and monitors, where it enhances user experience and saves power. Furthermore, its object detection capability up to 10 cm is utilized for features like touchless gesture control, presence detection (e.g., turning off a display when a user walks away), and simple obstacle avoidance in various devices.

2. In-Depth Technical Parameter Analysis

2.1 Electrical & Optical Specifications

All specifications are typically measured at VDD = 2.8V and an operating temperature (T_ope) of 25°C, unless otherwise stated.

Power Characteristics:
The sensor operates from a wide supply voltage range of 1.7V to 3.6V, compatible with common battery outputs and regulated power rails. The typical supply current during active measurement is 95 µA at maximum duty cycle. A significant feature for power saving is the standby (shutdown) mode, which draws a mere 1 µA. The wake-up time from this standby mode to active measurement readiness is typically 10 ms, allowing for rapid response while maintaining very low average power consumption.

Proximity Sensor (PS) Characteristics:
The PS function is highly configurable. The effective resolution is selectable between 8, 9, 10, and 11 bits, allowing designers to trade off measurement precision for conversion speed. The integrated IR emitter operates at a peak wavelength of 940 nm. The LED drive current is programmable in steps: 2.5, 5, 10, 25, 50, 75, 100, and 125 mA, enabling adjustment of detection range and power usage. The LED pulses at a frequency of 60 kHz to 100 kHz with a 50% duty cycle. The number of pulses per measurement cycle is configurable from 1 to 255, directly influencing integration time and sensitivity. Under typical conditions (32 pulses, 60 kHz, 100 mA drive, 18% gray card target), the sensor can detect objects at a distance of up to 10 cm. Its ambient light rejection is specified for up to 100 klux of direct sunlight.

2.2 Absolute Maximum Ratings and Operating Conditions

Absolute Maximum Ratings: These are stress limits that must not be exceeded, even momentarily, to prevent permanent damage. The supply voltage (VDD) must not exceed 4.0V. The digital I/O pins (SCL, SDA, INT) and the LDR pin have a voltage range of -0.5V to +4.0V. The device can be stored at temperatures between -40°C and +100°C.

Recommended Operating Conditions: These define the normal operating environment for reliable performance. VDD should be maintained between 1.7V and 3.6V. The LED anode supply (VLED) requires a separate 3.0V to 4.5V source. The I2C interface recognizes a logic high (V_I2Chigh) at ≥1.5V and a logic low (V_I2Clow) at ≤0.4V. The full operating temperature range is -40°C to +85°C, ensuring functionality in harsh environments.

2.3 AC Electrical Characteristics (I2C Interface)

The sensor supports both Standard mode (100 kHz) and Fast mode (400 kHz) I2C communication. Key timing parameters include: SCL clock frequency (f_SCL) from 0 to 400 kHz, bus free time (t_BUF) minimum of 1.3 µs, SCL low period (t_LOW) minimum of 1.3 µs, SCL high period (t_HIGH) minimum of 0.6 µs, and data setup time (t_SU:DAT) minimum of 100 ns. The rise and fall times for both SDA and SCL signals must be less than 300 ns. An input filter suppresses noise spikes shorter than 50 ns.

3. Performance Curve Analysis

The datasheet provides typical performance graphs essential for design.

PS Count vs. Distance: This curve illustrates the relationship between the raw digital output (PS count) from the sensor and the distance to a standard 18% reflectance gray card. The curve is typically non-linear, showing a rapid increase in count as distance decreases very close to the sensor, followed by a more gradual decline as distance increases. This graph is crucial for calibrating the sensor and setting appropriate interrupt thresholds for specific detection ranges in an application.

Emitter Angular Response: This diagram depicts the spatial radiation pattern of the built-in infrared LED. It shows the intensity of emitted IR light as a function of angle from the central axis (usually a polar plot). A typical pattern for this package might show a broad, Lambertian-like distribution. Understanding this pattern is vital for mechanical design, as it influences the effective field of view and detection zone of the proximity sensor. Proper alignment of any cover window or lens with this pattern is necessary to achieve the specified 10 cm range.

4. Mechanical and Package Information

The LTR-X130P is housed in an 8-pin ChipLED surface-mount package. The outline dimensions are provided in the datasheet with all measurements in millimeters. The dimensional tolerance for unspecified features is ±0.2 mm. The package is designed for standard automated pick-and-place and reflow soldering processes common in high-volume electronics manufacturing.

5. Soldering and Assembly Guidelines

While specific reflow profiles are not detailed in the provided excerpt, the device is intended for standard surface-mount technology (SMT) assembly. It is recommended to follow the JEDEC J-STD-020 guidelines for lead-free reflow soldering profiles. The moisture sensitivity level (MSL) should be confirmed from the full package specification. Devices are typically supplied in a dry-bag with desiccant and should be baked according to standard procedures if the bag's humidity indicator card shows excessive moisture exposure before use.

6. Packaging and Ordering Information

The standard packaging for the LTR-X130P is Tape and Reel, compatible with automated assembly equipment. Each reel contains 8000 units. The part number is LTR-X130P.

7. Application Design Recommendations

7.1 Typical Application Circuit

The recommended application circuit highlights critical design considerations. A fundamental requirement is the separation of the digital supply (VDD, 1.7-3.6V) and the LED anode supply (VLED, 3.0-4.5V). This separation is mandatory to ensure stable LED drive current and prevent noise from the LED pulses from coupling into the sensitive analog and digital supply rails. The circuit includes pull-up resistors (Rp1, Rp2, Rp3) on the SDA, SCL, and INT lines. Their value (1 kΩ to 10 kΩ) should be selected based on the total bus capacitance and desired rise time to meet I2C specifications. Decoupling capacitors are essential: a 1 µF ±20% X7R/X5R ceramic capacitor (C1) should be placed as close as possible to the VDD pin, and a 0.1 µF capacitor (C2) is also recommended. A similar 1 µF capacitor (C3) is used on the VLED line.

7.2 Pin Configuration and Function

• Pin 1 (SDA): I2C serial data line (bidirectional).
• Pin 2 (INT): Active-low interrupt output. Asserts when a programmable proximity event occurs.
• Pin 3 (LDR): Connects to the LED cathode. When using the internal driver, this pin is connected to Pin 4 (LEDK).
• Pin 4 (LEDK): LED cathode connection.
• Pin 5 (LEDA): LED anode connection. Must be supplied from the separate VLED rail (3.0-4.5V).
• Pin 6 (GND): System ground.
• Pin 7 (SCL): I2C serial clock input.
• Pin 8 (VDD): Digital power supply input (1.7-3.6V).

8. Technical Comparison and Differentiation

The LTR-X130P differentiates itself through high integration and robust performance in challenging conditions. Compared to discrete solutions (separate IR LED, photodiode, and signal conditioning IC), it offers a dramatically smaller footprint, simplified design-in process, and reduced bill of materials (BOM). Versus other integrated proximity sensors, its key advantages include the very high 100 klux ambient light immunity, which is superior to many competitors, and the flexible, programmable LED current and pulse count settings that allow fine-tuning for specific range, power, and response time requirements. The factory trimming ensures minimal unit-to-unit variation, improving manufacturing yield and consistency in end products.

9. Frequently Asked Questions (Based on Technical Parameters)

Q: Why must VDD and VLED be separate power rails?
A: The LED pulses can draw significant current (up to 125 mA). Sharing a supply rail would cause large voltage droops or noise on the VDD line, which could destabilize the sensitive analog front-end and digital logic of the sensor, leading to inaccurate readings or reset events. Separate rails isolate this noise.

Q: How do I increase the detection range beyond 10 cm?
A: The range is influenced by LED current, number of pulses, and target reflectance. To increase range, you can program a higher LED current (up to 125 mA) and/or increase the number of pulses per measurement (up to 255). Note that this will increase power consumption per measurement cycle.

Q: How does the interrupt function help save power?
A> Instead of the host microcontroller constantly polling the sensor for readings (keeping the I2C bus and CPU active), the sensor can be configured with upper and lower proximity thresholds. The host puts the sensor and itself into low-power mode. Only when an object enters or leaves the defined proximity zone does the sensor assert the INT line, waking the host to take action. This minimizes system activity.

Q: What is the purpose of the crosstalk cancellation feature?
A: In a compact package, some IR light from the internal emitter can directly leak or reflect internally onto the photodiode without hitting an external object. This creates a permanent offset or "crosstalk" signal. The sensor includes circuitry to measure and digitally subtract this offset, ensuring that the proximity count truly represents reflected light from an external object.

10. Design and Usage Case Studies

Case Study 1: Smartphone Display Management: In a smartphone, the LTR-X130P is placed near the earpiece. When the user brings the phone to their ear during a call, the sensor detects the proximity of the head (within ~2-5 cm). It triggers an interrupt to the application processor, which then turns off the display touchscreen to prevent accidental cheek touches and dims the backlight to save power. When the phone is moved away, the display is restored.

Case Study 2: Interactive Kiosk Presence Detection: A public information kiosk uses the sensor to detect when a person approaches within 50 cm. Upon detection, it wakes from a low-power sleep state, activates the display, and shows an attractor loop. If no one is detected for a set period, it returns to sleep, significantly reducing energy consumption compared to running 24/7.

11. Principles of Operation

The LTR-X130P operates on the principle of active infrared proximity sensing and photometric ambient light sensing. For proximity measurement, the internal microcontroller triggers the integrated IR LED to emit a series of modulated pulses at 940 nm. Any object in front of the sensor reflects a portion of this light back. The dedicated IR-sensitive photodiode converts the reflected light intensity into a small photocurrent. This current is integrated and converted into a digital value by a high-resolution ADC. The strength of this digital value (PS count) is proportional to the reflectivity and proximity of the object. The sensor simultaneously measures ambient light using a separate visible-light photodiode, whose output is processed to subtract the ambient IR component from the proximity signal, enhancing accuracy.

The I2C communication follows standard protocols. The device has a fixed 7-bit slave address of 0x53. The master controller uses this address to write configuration registers (e.g., setting LED current, pulse count, interrupt thresholds) and to read back proximity and ambient light data. The read and write protocols, including single writes, sequential writes, and combined format reads (repeated START), are implemented as per the I2C specification.

12. Technology Trends

The evolution of sensors like the LTR-X130P follows several clear industry trends. There is a continuous drive towards higher integration, combining more functions (e.g., color sensing, gesture recognition) into single packages while shrinking the footprint. Power efficiency remains paramount, pushing for lower active and standby currents and smarter wake-up schemes. Performance in extreme environments is improving, with better sunlight immunity and wider temperature ranges. Furthermore, there is a trend towards "smarter" sensors with embedded algorithms that provide higher-level, pre-processed data (e.g., "object present/absent" flags instead of raw counts) to offload processing from the main application processor and simplify software development.