原标题：Linear LTC2508-32低噪低功耗32位ADC解决方案

　　Linear公司的LTC2508-32是集成了可配置数字滤波器的低噪音低功耗高性能32位ADC,工作电压2.5V,VREF范围从2.5V到5.1V,全差分输入范围高达±VREF,±0.5ppm INL (Typ),61sps时的动态范围145dB,主要用在地震学,能源勘探,自动测试设备(ATE)和高精度仪器.本文介绍了LTC2508-32主要特性,功能框图,以及演示板主要特性,电路图和PCB设计图.

　　The LTC®2508-32 is a low noise, low power, high-performance32-bit ADC with an integrated configurable digitalfilter. Operating from a single 2.5V supply, the LTC2508-32　features a fully differential input range up to ±VREF,withVREF ranging from 2.5V to 5.1V. The LTC2508-32 supportsa wide common mode range from 0V to VREF simplifying　analog signal conditioning requirements.

　　The LTC2508-32 simultaneously provides two outputcodes: (1) a 32-bit digitally filtered high precision lownoise code, and (2) a 22-bit no latency composite code.

　　The configurable digital filter reduces measurement noiseby lowpass filtering and down-sampling the stream ofdata from the SAR ADC core, giving the 32-bit filteredoutput code. The 22-bit composite code consists of a14-bit code representing the differential voltage and an8-bit code representing the common mode voltage. The22-bit composite code is available each conversion cycle,with no cycle of latency.

　　The digital filter can be easily configured for 4 differentdown-sampling factors by pin strapping. The configurationsprovide a dynamic range of 131dB at 3.9ksps and145dB at 61sps. The digital lowpass filter relaxes the requirementsfor analog anti-aliasing. Multiple LTC2508-32devices can be easily synchronized using the SYNC pin.

　　LTC2508-32主要特性:

　　±0.5ppm INL (Typ)

　　145dB Dynamic Range (Typ) at 61sps

　　131dB Dynamic Range (Typ) at 4ksps

　　Guaranteed 32-Bits No Missing Codes

　　Configurable Digital Filter with Synchronization

　　Relaxed Anti-Aliasing Filter Requirements

　　Dual Output 32-Bit SAR ADC

　　32-Bit Digitally Filtered Low Noise Output

　　14-Bit Differential + 8-Bit Common Mode 1MspsNo Latency Output

　　Wide Input Common-Mode Range

　　Guaranteed Operation to 85℃

　　1.8V to 5V SPI-Compatible Serial I/O

　　Low Power: 24mW at 1Msps

　　24-Lead 7mm × 4mm DFN Package

　　LTC2508-32应用:

　　Seismology

　　Energy Exploration

　　Automated Test Equipment (ATE)

　　High-Accuracy Instrumentation

　　图1.LTC2508-32功能框图

　　图2.LTC2508-32典型应用电路图

　　演示板DC2222A

　　Demonstration circuit 2222A features the LTC2508-32 and LTC2512-24 ADCs. The LTC2508-32 and LTC2512-24 are low power, low noise, high speed, 32-bit/24-bit SAR ADCs with an integrated configurable digital averaging filter that operate from a single 2.5V supply. The following text refers to the LTC2508-32 but applies to both parts, the only difference being sample rate and number of bits. The DC2222A demonstrates the DC and AC performance of the LTC2508-32 in conjunction with the DC590 or DC2026 QuikEvalTM and DC890 PScopeTM data collection boards. Use the DC590 or DC2026 to demonstrate DC performance such as peak-to-peak noise and DC linearity.

　　Use the DC890 if precise sampling rates are required or todemonstrate AC performance such as SNR, THD, SINADand SFDR. The DC2222A is intended to show recommended　grounding, component placement and selection, routingand bypassing for this ADC.

　　图3.演示板DC2222A外形图

　　图4.演示板DC2222A-B电路图(1)

　　图5.演示板DC2222A-B电路图(2)

　　图6.演示板DC2222A-B电路图(3)

　　图7.演示板DC2222A-C电路图(1)

　　图8.演示板DC2222A-C电路图(2)

　　图9.演示板DC2222A-C电路图(3)

　　图10.演示板DC2222A PCB设计图(1)

　　图11.演示板DC2222A PCB设计图(2)

　　图12.演示板DC2222A PCB设计图(3)

　　图13.演示板DC2222A PCB设计图(4)

　　图14.演示板DC2222A PCB设计图(5)

　　图15.演示板DC2222A PCB设计图(6)

　　图16.演示板DC2222A PCB设计图(7)

　　图17.演示板DC2222A PCB设计图(8)

　　图18.演示板DC2222A PCB设计图(9)

　　图19.演示板DC2222A PCB设计图(10)

　　图20.演示板DC2222A PCB设计图(11)