LTC1865 16BIT 250k ADC

LTC1865 16 Bit 250ksps ADC 2 Channel SPI Analog to Digital Converter IC SO-8 5V

LTC1865CS8 Data Acquisition Vibration Audio Sampling Weighing Sensor Battery Current Voltage Monitoring Portable Instrument Isolated Differential Input SOIC

     The LTC1865 (LTC1865CS8#PBF), made by Linear Technology (Analog Devices), is a 16 bit, 2 channel analog to digital converter (ADC) IC that can take 250,000 samples per second (250ksps). It runs on a single 5V supply and draws only 850µA (typical) at 250ksps. Since it automatically goes to sleep after each conversion, the current drops further at lower sample rates; at 1ksps it falls to about 2µA.

     The IC uses successive approximation (SAR) architecture and includes a sample-and-hold circuit. Its two analog inputs (CH0, CH1) are selected with a 2 bit configuration word sent on the SDI line: each channel can be measured single-ended against GND, or the two channels can be used together as a differential input. Data is read over an SPI / MICROWIRE compatible serial interface with the CONV, SCK, SDI and SDO lines; the clock can go up to 20MHz.

     This product is the SO-8 package version: the reference input is tied internally to VCC, so the measuring range is 0V - VCC (0V - 5V with a 5V supply). Its high impedance inputs can be connected directly to the signal source. It suits high speed data acquisition, portable instruments, battery operated measuring devices and isolated or remote data acquisition circuits. It is pin compatible with the 12 bit LTC1861 and the manufacturer lists it as a 16 bit upgrade for the 12 bit LTC1286 / LTC1298 (control signal and data word differ, so the software must be adapted).

Key features:

     16 bit, 250ksps: 16 bit conversion up to 250,000 samples per second; conversion time typically 2.75µs. Vibration, audio and fast changing signals can be sampled.

     Very low current: Typically 850µA at 250ksps; it sleeps automatically between conversions and current drops to about 2µA at 1ksps. Suitable for battery powered devices.

     2 channels selected by software: CH0 and CH1 are measured single-ended or used as a differential pair; the selection is made with 2 bits sent on the SDI line, no external multiplexer is needed.

     SPI / MICROWIRE serial interface: Connects to the microcontroller with the CONV, SCK, SDI and SDO lines; the clock can go up to 20MHz.

     Single 5V supply: Runs on a single 4.75V - 5.25V supply; in the SO-8 version the reference is tied to VCC, so no separate reference IC is needed.

Features:

• Product type:    16 bit 2 channel SAR ADC (analog to digital converter) IC
• Part number: LTC1865CS8#PBF (marking: 1865)
• Manufacturer: Linear Technology (Analog Devices)
• Resolution: 16 bit (no missing codes resolution at least 14 bit)
• Sample rate: 250ksps max
• Number of channels: 2 (CH0, CH1); single-ended or differential, selected by software
• Input range: 0V - VCC (in the SO-8 version the reference is tied internally to VCC)
• Supply voltage: 5V (4.75V - 5.25V)
• Supply current: typical 850µA (250ksps); about 2µA at 1ksps
• Conversion time: typical 2.75µs, max 3.2µs
• Integral nonlinearity (INL): ±8LSB max
• Signal to noise ratio (SNR): typical 87dB
• Offset error (SO-8): typical ±3mV, max ±7mV
• Input capacitance: 12pF (in sample mode)
• Interface: SPI / MICROWIRE compatible 3 wire serial interface + CONV, clock 20MHz max
• Pinout: 1 CONV, 2 CH0, 3 CH1, 4 GND, 5 SDI, 6 SDO, 7 SCK, 8 VCC (VREF)
• Compatibility: pin compatible with 12 bit LTC1861; 16 bit upgrade for LTC1286 / LTC1298 (software must be adapted)
• Package: 8 lead plastic SO-8 (SOIC, 150mil, 3.90mm body width), surface mount (SMD)
• Operating temperature: 0°C - 70°C (C grade)
• Dimensions: about 4.9mm x 3.9mm body, about 6mm width including leads

Usage information:

• Apply a clean 5V supply to pin 8 (VCC) and connect this pin to analog GND with a decoupling capacitor placed right next to the IC. In the SO-8 version the reference is VCC, so measurement accuracy depends directly on the accuracy and noise of the supply voltage.
• Start a conversion by pulling the CONV pin high; when the conversion is finished pull CONV low and read the 16 bit result from SDO with SCK. The first 2 bits sent on SDI at the same time (SGL/DIFF, ODD/SIGN) select the channel of the next conversion.
• For single-ended measurement set SGL/DIFF = 1; ODD/SIGN = 0 selects CH0, 1 selects CH1. For differential measurement set SGL/DIFF = 0; with ODD/SIGN = 0, CH0 is the positive and CH1 the negative input (reversed when 1). Differential measurement is unipolar: the positive input may be 0V - VCC above the negative input, and the negative input must stay within 0V - VCC/2.

Application areas:

•  Data acquisition boards and fast data loggers
•  Vibration and acceleration signal sampling
•  Audio and acoustic signal sampling
•  Weighing and load cell reading (with a suitable amplifier)
•  High resolution reading of sensor outputs
•  Battery and cell voltage measurement
•  Current and voltage monitoring circuits
•  Portable and battery powered instruments
•  Isolated and remote data acquisition circuits

Precautions:

•  This product is not a ready module but a bare SMD (SO-8) IC; it must be soldered to your board. Use an SO-8 to DIP adapter board to try it on a breadboard.
•  Do not apply voltage outside the 0V - VCC range to the analog inputs (absolute limit GND - 0.3V to VCC + 0.3V); the supply voltage must never exceed 7V.
•  The SO-8 version has no separate reference pin and the measuring range equals VCC; if a reference other than 5V or a precision reference is needed, the MSOP package version is required.
•  For 16 bit accuracy route analog and digital lines separately, use a GND plane and keep the supply free of noise; a noisy supply directly corrupts the measured value.
•  The IC is sensitive to static electricity; handle and solder it with antistatic precautions.

Package contents:

•  1 Pcs LTC1865 16 Bit 250ksps ADC IC (SO-8)
•  Note: SO-8 to DIP adapter board and circuit board are not included in the package.