LTR-X1503 Optical Sensor Datasheet - Integrated Ambient Light and Proximity Sensing - I2C Interface - 3.0-3.6V - Technical Documentation

1. Product Overview

LTR-X1503 is a highly integrated, low-voltage optical sensor that combines an ambient light sensor, a proximity sensor, and a built-in infrared emitter into a single miniature, chip-scale, lead-free surface-mount package. This integrated design simplifies circuit design and saves valuable board space for compact electronic devices.

The core advantage of this sensor lies in its dual functionality. The ambient light sensor provides a linear photometric response over a wide dynamic range, making it suitable for various ambient lighting conditions from extremely dark to extremely bright. Simultaneously, the built-in proximity sensor can detect the presence or absence of objects within a user-configurable distance, enabling features such as screen blanking during calls or touchscreen deactivation.

This device is primarily targeted at the mobile, computing, and consumer electronics markets. Its ultra-small size, low-power characteristics with a sleep mode, and I2C digital interface make it an ideal choice for smartphones, tablets, laptops, wearable devices, and IoT devices, where efficient power management and space utilization are key constraints.

1.1 Core Features and Advantages

• Single Package Dual Sensing:Integrates ambient light sensing and proximity sensing, reducing component count and PCB footprint.
• Digital I2C Interface:Supports Standard mode (100kHz) and Fast mode (400kHz), facilitating communication with the host microcontroller.
• Ultra-Low Power Operation:Features operational and standby modes. The typical supply current for both sensors operating simultaneously is 160 uA, while the standby current can drop to as low as 1 uA, significantly extending battery life.
• Programmable Interrupt Feature:The proximity sensor incorporates an interrupt system with programmable upper and lower thresholds and hysteresis. This eliminates the need for the main processor to continuously poll the sensor, thereby enhancing overall system efficiency and power savings.
• High-Performance Ambient Light Sensor:Provides 16-bit effective resolution with a linear response over a wide range and a spectral response close to the human eye. It includes automatic suppression of 50Hz/60Hz lighting flicker to ensure stable readings under artificial light sources.
• Robust proximity sensing:Includes a built-in LED driver, high ambient light rejection capability (up to 10 klux), 16-bit resolution, and a crosstalk cancellation algorithm for reliable object detection.
• Factory calibration:One-time factory trimming minimizes device-to-device variation, ensures consistent performance, and reduces the manufacturing calibration requirements for end customers.
• Wide Operating Range:Operating voltage range from 3.0V to 3.6V, temperature range from -40°C to +85°C, with built-in temperature compensation circuitry to ensure stable operation.

2. Detailed Technical Specifications

2.1 Absolute Maximum Ratings

Stressing the device beyond these limits may cause permanent damage.

• Power supply voltage (VDD):3.6 V
• Digital I/O pins (SCL, SDA, INT):Suitable for normal operation of the device.
• LED anode voltage (V_LED):-0.5 V to 4.6 V
• LED driver pin voltage (V_LDR):-0.5 V to 3.6 V
• Storage temperature:-40°C to 100°C
• ESD Protection (HBM):2000 V

2.2 Recommended Operating Conditions

For normal device operation.

• Power supply voltage (VDD):3.0 V to 3.6 V
• LED supply voltage (V_LED):2.8 V to 4.0 V
• Operating Temperature:-40°C to 85°C
• I2C High-Level Input:1.5 V to VDD
• I2C Low-Level Input:0 V zuwa 0.4 V

2.3 Electrical and Optical Specifications

Ana bayar da ƙayyadaddun yawanci a ƙarƙashin VDD = 1.8V kuma Ta = 25°C.

2.3.1 Power Consumption Characteristics

• Supply Current (Both ALS and PS Active):160 uA (Typical, with a measurement repetition rate of 100ms).
• ALS Operating Current:160 uA (Typical).
• PS Operating Current:57 uA (typical value, 8 pulses, 100% duty cycle, 32us pulse width).
• Standby current:1 uA (typical value).
• Wake-up time from standby:0.25 ms (typical).

2.3.2 Ambient Light Sensor Characteristics

• Resolution:Programmable to 13, 14, 15, or 16 bits of effective resolution.
• Lux Accuracy:±10% (typical, under white LED illumination).
• Dark Level Count:0 to 5 counts (at 0 lux, 16-bit resolution, 512x gain, 100ms integration time).
• Integration Time:Programmable, ranging from 0.2 ms to 200 ms.
• Flicker Noise Suppression:For 50Hz/60Hz illumination, the error is ±5%.
• Spectral Response:Approaching the photopic response of the human eye.

2.3.3 Proximity Sensor Characteristics

• Resolution:16-bit effective resolution.
• Peak Sensitivity Wavelength:940 nm (typical, for integrated IR emitter).
• Detection Distance:Up to 20 cm (typical, configurable based on pulse count, gain, and current settings).
• LED pulse current:Programmable, up to 186 mA (typical).
• LED pulse width:Programmable: 8, 16, 32, or 64 us.
• LED Pulse Count:Programmable, 1 to 256 pulses per measurement.
• Ambient Light Suppression:Up to 10 klux (direct sunlight). When this level is exceeded, a fail-safe function prevents false triggering.

3. Performance Curve Analysis

3.1 ALS Spectral Response

The ambient light photodiode of this sensor is designed with a filter that matches the CIE photopic luminosity function, which defines the standard response of the human eye to light. This ensures that the lux readings reported by the sensor accurately represent the brightness perceived by humans, not just the raw radiant energy. This is crucial for achieving automatic display brightness control that feels natural to the user.

3.2 PS Performance vs. Distance Relationship

The performance characteristic of a proximity sensor is represented as a function of the reflected signal strength versus the distance to a standard reflective object (typically with 88% reflectivity). This relationship is nonlinear and follows the inverse square law. The graph shows that under typical settings (e.g., VDD=1.8V, LED current 104mA, 16 pulses), a clear and measurable signal can be obtained, allowing for the setting of a reliable detection threshold for specific application distances (e.g., 5cm for phone earpiece detection).

3.3 ALS Angular Response

传感器的角度响应图（针对X轴和Y轴）显示了测量光强如何随入射角变化。对于大多数环境光传感应用，完美的余弦（朗伯）响应是理想的。LTR-X1503表现出接近这种理想的响应，确保无论主光源相对于传感器的方向如何，都能获得准确的读数。在极端角度（> ±60度）下与理想余弦响应的偏差，由于封装和光学设计的限制，在大多数传感器中是典型的。

4. Mechanical and Packaging Information

The LTR-X1503 comes in an ultra-small 8-pin chip-scale surface-mount package. The exact outline dimensions are provided in the datasheet's dimensional drawings, which include top, side, and bottom views with key dimensions annotated, such as package length, width, height, lead pitch, and pad size. This information is crucial for PCB footprint design and ensuring proper mechanical fit within the final product.

4.1 Pin Configuration and Functions

• Pin 1 (VDD):Power Input (3.0V - 3.6V).
• Pin 2 (SCL):I2C Serial Clock Input.
• Pin 3 (GND):Ground connection.
• Pin 4 (LEDA):Anode connection for the integrated infrared LED. Must be connected to the LED power rail (V_LED).
• Pin 5 (LDR):LED driver connection. Since the driver is built-in, this pin should be left unconnected (NC).
• Pin 6 (NC):Ba shi ciki haɗi. Ana iya rataye ko kafa ƙasa.
• Pin 7 (INT):Fitilar fitarwa ta katse mai ƙarancin ƙarfi. Lokacin da abin ya kusa (ganowa/cire abu) ya faru bisa ga bakin kofa da aka tsara, wannan fitarwa mai buɗe rami tana saita zuwa ƙarancin ƙarfi.
• Pin 8 (SDA):I2C serial data input/output (open drain).

5. Application Circuit and Design Guide

5.1 Recommended Application Circuit

Typical application circuits include sensors, necessary decoupling capacitors, and I2C pull-up resistors.

• Power Supply Decoupling:A 1uF ceramic capacitor (C1) should be placed as close as possible between VDD and GND. An additional 0.1uF capacitor (C2) can be added to suppress high-frequency noise.
• LED power supply decoupling:It is recommended to place a 1uF capacitor (C3) between the LEDA pin (and the V_LED power rail) and GND.
• I2C pull-up resistors:Resistors (Rp1, Rp2) with values between 1 kΩ and 10 kΩ are required on the SCL and SDA lines. The specific value depends on the bus capacitance and the required rise time; a lower value provides stronger pull-up capability but increases current consumption. If an INT line is used, a similar pull-up resistor may also be required.

5.2 Power Sequence

Key Requirements:The correct power sequence must be followed to prevent potential latch-up or damage.

• Power-on:VDD (main logic power supply) must beBefoPower on.
• Power outage:V_LED must be withinBefo VDD.

Power off.

6. Soldering and Assembly Guide

This component is a surface-mount device designed for the reflow soldering process common in high-volume electronics manufacturing.

6.1 Reflow Soldering Temperature Profile

• Although specific data sheets may not detail the temperature profile, the standard lead-free (RoHS compliant) reflow soldering profile is applicable. This typically includes:Preheating/Ramp-up:
• A slow ramp-up (1-3°C/second) to approximately 150-200°C to activate the flux and minimize thermal shock.Soaking Zone:
• Maintain a plateau at 150-200°C for 60-120 seconds to ensure uniform temperature across the entire circuit board and to evaporate volatiles.Reflow Zone:
• Rapidly heat to the peak temperature. The peak temperature must not exceed the maximum rating of the package (which may be 260°C for a short time, e.g., 10-30 seconds above 245°C).Cooling:

Controlled cooling phase.

Please refer to the package's Moisture Sensitivity Level. If the device is exposed to ambient humidity exceeding its rated threshold, follow the appropriate baking and handling procedures.

6.2 Storage Conditions

7. Packaging and Ordering Information

LTR-X1503 is supplied in tape and reel format suitable for automatic placement machines.

• Part Number:LTR-X1503
• Packaging Type:8-pin chip-scale package.
• Package:Reel.
• Standard quantity per reel:3,000 pieces.

8. Application Recommendations

8.1 Typical Application Scenarios

• Smartphones/Tablets:Automatic Screen Brightness Adjustment (ALS) and Screen Off/Touch Deactivation (PS) when bringing the device close to the ear during a call.
• Laptop and Monitor:Dynamic backlight adjustment based on ambient light to save power and improve viewing comfort.
• Wearable Devices:Display activation (PS) upon gesture wake-up or user gaze at the device, along with brightness management.
• Consumer Electronics:Automatic switch control, contactless switching, and presence detection in home appliances.

8.2 Zane da Kyakkyawan Aiki

• Optical Path:Ensure the ambient light sensor has a clear, unobstructed optical path. For proximity sensors, design a window or aperture so that infrared light can be emitted effectively and the reflected light can return effectively. Avoid placing the sensor behind dark or infrared-absorbing materials.
• Infrared Interference:The proximity sensor uses 940nm infrared light. Sunlight and some artificial light sources contain infrared components. The sensor's high ambient light suppression and crosstalk cancellation features help, but keeping it away from direct, intense infrared light sources can improve performance.
• I2C Bus Management:Use the interrupt function to put the main MCU to sleep, waking it only when a proximity event occurs. Poll the ambient light sensor at a moderate rate (e.g., once per second), unless tracking rapid brightness changes is required.
• Threshold Calibration:The proximity sensor's detection threshold must be calibrated inside the final product enclosure to account for cover glass thickness, reflectivity, and internal reflection (crosstalk). This is typically done during the manufacturing process.

9. Technical Comparison and Differentiation

LTR-X1503 competes in the integrated ALS/PS solution market. Its main differentiation advantages may include:

• High Integration:Integrating the infrared emitter and sensor within the same package is a significant advantage, reducing the bill of materials and simplifying optical alignment compared to solutions requiring discrete infrared LEDs.
• Performance:Both sensors feature 16-bit resolution, high ambient light suppression (10 klux), and programmable measurement parameters, offering design flexibility and robust performance.
• Energy Efficiency:Competitive low operating current and standby current are crucial for battery-powered devices.
• Digital Interface:The I2C interface is a standard and widely supported bus, making integration simple and straightforward.

10. Frequently Asked Questions (Based on Technical Parameters)

10.1 How to set the detection distance of a proximity sensor?

Detection distance is not a single fixed parameter, but the result of multiple configurable settings: LED pulse current, pulse width, pulse count, and receiver gain. By increasing LED current, pulse count, or gain, the reflected signal strength increases, enabling detection of objects at greater distances or with lower reflectivity. The specific "detection" threshold is set by the user in the interrupt threshold register by characterizing the proximity sensor data counts at the desired distance in the final product.

10.2 Why is the power sequence between VDD and V_LED important?

Incorrect sequencing can cause large surge currents to flow through internal ESD protection structures or logic circuits, potentially triggering latch-up—a high-current state that can damage the device. Following the specified sequence (VDD on before V_LED on; V_LED off before VDD off) ensures internal transistors are correctly biased before the higher-voltage LED supply is applied or removed.

10.3 What does "crosstalk cancellation" mean for proximity sensors?

Crosstalk refers to internal reflections within the device module or its cover, where infrared light from the emitter reaches the proximity sensor photodiode without being reflected by an external object. This creates a background offset that can cause false triggers or reduce sensitivity. The LTR-X1503 employs algorithms (typically involving baseline measurements with the LED off) to measure and subtract this crosstalk component from the final proximity sensor data, thereby improving the accuracy of object detection.

10.4 Yadda Sensor na Haske na Muhalli zai yi hana flicker na 50/60Hz?

Fitilun incandescent da na fluorescent waɗanda ke samun wutar lantarki na AC suna yin saɓo a 100Hz ko 120Hz (sau biyu na mitar layin). Idan lokacin haɗakar na'urar binciken ya kasance lamba mai cikakken lokacin ƙyalli (misali, 10ms, 20ms, 100ms), zai yi matsakaicin cikakken lokacin haske, don haka ya daidaita saɓo kuma ya ba da karatun lux mai tsayi. Lokacin haɗakar na'urar binciken ana iya shirya shi azaman lamba mai cikakken waɗannan lokutan, don aiwatar da irin wannan hana.

11. Nazarin Shari'a na Zane da Amfani

11.1 Energy-Efficient Display Control Implementation in Smartwatches

Scenario:Smartwatches need to maximize battery life. The display should be bright outdoors, dim indoors, and turn off completely when not viewed (e.g., when the user's arm is lowered).

Realize using LTR-X1503:

1. ALS role:The ambient light sensor is configured with 16-bit resolution and 100ms integration time (for flicker suppression). The main MCU reads the ambient light sensor data via I2C once per second. The lux value is mapped to the corresponding PWM duty cycle for the display backlight via a lookup table or algorithm to achieve smooth automatic brightness adjustment.
2. PS Role:The proximity sensor is configured with appropriate pulse current and quantity based on the expected viewing distance (e.g., approximately 30cm). Set interrupt thresholds: a lower threshold for "object removal" (not viewing the watch) and an upper threshold for "object detection" (raising the watch to view). The INT pin is connected to a GPIO with wake-up capability on the MCU.
3. Energy-saving workflow:
   • Mtumiaji anaposhusha mkono, hesabu ya kihisi cha karibu hushuka chini ya kizingiti cha chini, na kusababisha usumbufu.
   • MCU inaamka kutoka usingizi, inasoma hali ya usumbufu, na kuamuru skrini iingie katika hali ya nguvu ndogo ya kuzima.
   • Then the MCU can put itself and the sensors (possibly except for the low-power proximity sensor monitoring mode) back to sleep.
   • When the user raises their arm to look at the watch, the proximity sensor detects an object, triggers an interrupt, wakes up the MCU, which then fully powers the display and the ambient light sensor to show the correct time at an appropriate brightness.

Compared to an always-on or time-only controlled display, this combination significantly reduces the system's average power consumption.

12. Introduction to Working Principles

12.1 Ambient Light Sensing Principle

The ambient light sensing function is based on a photodiode, a semiconductor device whose generated tiny current is proportional to the light intensity shining on it. In the LTR-X1503, this photodiode is covered with a filter that mimics the sensitivity of the human eye across the entire visible spectrum. The generated photocurrent is very small (picoamps to nanoamps). An integrated transimpedance amplifier converts this current into a voltage, which is then digitized by a high-resolution analog-to-digital converter. The digital value is processed and made available via I2C registers, representing illuminance in counts, which can be converted to lux units using a calibration formula.

12.2 Proximity Sensing Principle

The proximity sensor operates based on the active infrared reflection principle. An integrated infrared LED emits short pulses of 940nm light, invisible to the human eye. A separate, dedicated photodiode (different from the ambient light sensing diode) acts as the receiver. When an object is within range, part of the emitted infrared light reflects off the object and returns to the receiver photodiode. The sensor measures the amount of reflected light received during and after each LED pulse. By comparing this signal with the ambient infrared level (measured with the LED off) and after crosstalk cancellation, the sensor calculates a proximity data count. A higher count indicates a closer object or higher reflectivity. This count is compared to a user-programmed threshold to trigger an interrupt.

13. Technology Trends

The market for integrated optical sensors like the LTR-X1503 is driven by several distinct trends in the electronics industry:

• Miniaturization:The ongoing demand for smaller package sizes (e.g., chip-scale) to accommodate increasingly thinner devices with larger screens and batteries.
• Increased Integration:Trend is moving beyond simply combining ambient light sensing and proximity sensing. Future sensors may integrate more environmental sensors (color, gesture, time-of-flight), further reducing system complexity.
• Edge Intelligence:Sensors are gaining more on-chip processing capabilities. Future versions may not only provide raw data but also internally perform lux calculations, proximity state machine logic, and gesture recognition, sending only high-level event notifications to the main processor, thereby further saving system power.
• Performance Improvements:Expectations for precision, dynamic range, and power consumption continue to rise. Advances in semiconductor processes and optical design are enabling ADCs with lower noise and higher resolution, as well as more efficient LEDs.
• Standardization and Software Support:Robust and standardized software drivers (e.g., for Android, Linux) are becoming as crucial as hardware performance, reducing time-to-market for device manufacturers.