新一代智能电子化学传感器的新型传感器接口IC ADuCM355详解

ADI公司的ADuCM355是新一代智能电子化学传感器的新型传感器接口IC，能够在单个芯片上同时实现恒电位仪和电化学阻抗频谱分析仪（EIS）功能的唯一解决方案。器件集成了行业最先进的传感器诊断技术，具有卓越的低噪声和低功耗性能，并且尺寸最小，显著节约成本。主要用在工业气体检测，仪器仪表，生命体征监测和疾病管理等。本文介绍了ADuCM355主要特性，功能框图，应用电路以及评估板EVAL-ADuCM355QSPZ主要特性和应用连接图。

The ADuCM355 is an on-chip system designed to control andmeasure electrochemical and biosensors. The ADuCM355 is an ultralow power mixed-signal microcontroller based on theARMRCortex™-M3 processor. It is designed with current， voltage， and impedance measurement capability. The ADuCM355 features a 16-bit， 400 kSPS multichannel successive approximation register （SAR） analog-to-digitalconverter （ADC） with input buffers， built in antialias filter（AAF） and programmable gain amplifier （PGA）。 The current inputs include three transimpedance amplifiers （TIA） with programmable gain and load resistors for measuring differentsensor types. The analog front end （AFE） also contains twomore low power amplifiers designed specifically for potentiostat capability to maintain a constant bias voltage to an external electrochemical sensor. The noninverting inputs of these twoamplifiers are controlled by on-chip dual output digital-to-analog converters （DAC）。 The analog outputs include anotherhigh speed DAC and output amplifier designed to generate an ac signal. The ADC is capable of operating at conversion rates up to 400 kSPS with an input range of ±0.9 V. An input mux before the ADC allows the user to select an input channel formeasurement. These input channels include three externalcurrent inputs， multiple external voltage inputs， and internal channels. The internal channels allow diagnostic measurementsof the internal supply voltages， die temperature， and referencevoltages. Two of the three voltage DACs are dual output， 12-bit stringDACs. One output per DAC controls the noninverting input of a potentiostat amplifier， and the other controls the noninverting input of the TIA.

The third DAC （sometimes referred to as the high speed DAC）is designed for the high power TIA for impedancemeasurements. Its output frequency range is up to 200 kHz. A precision 1.82 V and 2.5 V on-chip reference source is available. The internal ADC and VDAC circuits use this on-chip reference source to ensure low drift performance for all of these peripherals.

The ADuCM355 integrates a 26 MHz ARM Cortex-M3processor. It is a 32-bit reduced instruction set computer （RISC） machine， offering up to 32.5 DMIPS peak performance. The ARM Cortex-M3 processor also has a flexible multichannel direct memory access controller （DMA） supporting serial peripheral interface （two independent SPI ports）， universalasynchronous receiver/transmitter （UART）， and I2Ccommunication peripherals. The ADuCM355 has 128 kB of nonvolatile flash/EE memory and 64 kB of SRAM integrated on-chip. The digital processor subsystem is clocked from a 26 MHz on-chip oscillator. This is the source of the main digital die systemclock. Optionally， a 26 MHz PLL can be used as the digitalsystem clock. This clock can be internally subdivided so that the processor operates at a lower frequency and saves power. A lowpower internal 32 kHz oscillator is available and can clock thetimers. The ADuCM355 includes three general-purpose timers，a wake-up timer （which can be used as a general-purposetimer）， and a system watchdog timer. The analog subsystem has a separate 16 MHz oscillator used to clock the ADC， DACs， and other digital logic on the analog die.

The analog die also contains a separate 32 kHz， low poweroscillator to clock a watchdog timer on the low voltage die. Both the 32 kHz oscillator and this watchdog are independent from the digital die oscillators and system watchdog timer. A range of communication peripherals can be configured asrequired in a specific application. These peripherals includeUART， I2C， 2xSPI， and GPIO ports. The GPIO， combined with the general-purpose timers， can be combined to generate apulse width modulation （PWM） type output. On-chip factory firmware supports in-circuit erasing of user flashtriggered via the UART， while nonintrusive emulation and programdownload are supported via the serial wire debug port （SW-DP） interface. The ADuCM355 operates from 2.8 V to 3.6 V supply and isspecified over a temperature range of −40℃ to +85℃。 The chip is packaged in a 72-lead 6 mm × 5 mm land grid array （LGA）package.

ADuCM355主要特性：

Analog input/output

16-bit， 400 kSPS ADC

Voltage， current， and impedance measurement capability

Internal/external current and voltage channels

Ultralow leakage switch matrix and input mux

Input buffers， programmable gain amplifier

Voltage DACs

2 dual output VDACs Output range 0.2 V to 2.4 V （±2.2 V voltage potential to sensor）

2 bias potentiostat and TIA amplifiers

Ultralow power， 1 μA per DAC

One high speed 12-bit VDAC

Output range to sensor ±607 mV

High speed TIA for impedance measurements

Programmable gain amplifier on output

Amplifiers， accelerators， and references 2 low power， low noise amplifiers

Suitable for potentiostat bias in electrochemical sensing

2 low power， low noise TIAs Suitable for measuring sensor current output 200 pA to 3 mA range Programmable load and gain resistors Analog hardware accelerators DDS waveform generator

DFT and digital filters 2.5 V and 1.82 V on-chip， precision voltage references Internal temperature sensor， ±2℃ accurate

Impedance measurement range of 《1 Ω to 10 MΩ， 1 Hz to 200 kHz

Voltammetry scan rate up to 2000 steps per second

Microcontroller

26 MHz ARM Cortex-M3 processor

Serial wire port supports code download and debug

128 kB flash/64 kB of SRAM

Security/safety

Hardware crypto accelerator with AES-128 and AES-256

Hardware CRC with programmable polynomial generator Read/write protection of user flash

On-chip peripherals

UART， I2C， and SPI serial input/output

Up to 10 GPIO pins

External interrupt option

General-purpose， wake-up， and watchdog timers

Power

2.8 V to 3.6 V supply and active measurement range

Power-supply monitor

Active current consumption 30 μA/MHz for digital part

Hibernate with bias to external sensor， 8.5 μA

Shutdown mode with no SRAM retention， 2 μA

Packages and temperature range

6 mm × 5 mm， 72-lead LGA package

Fully specified for −40℃ to +85℃ ambient operation

ADuCM355应用：

Gas detection Food quality

Environmental sensing （air， water， soil）

Blood glucose meters

Life sciences and biosensing analysis

Bioimpedance measurements

General Amperometry， voltammetry， and impedance

spectroscopy functions

图1.ADuCM355简化功能框图

图2.ADuCM355功能框图

图3.ADuCM355推荐的外接元件连接图

评估板EVAL-ADuCM355QSPZ

The ADuCM355 system on a chip provides the features needed to bias and measure a range of different electrochemical sensors. The EVAL-ADuCM355QSPZ allows users to evaluate the performance of the ADuCM355 when implementing a range of different electrochemical techniques， including chronoam-perometry， voltammetry， and electrochemical impedance spectroscopy （EIS）。

评估板EVAL-ADuCM355QSPZ主要特性：

Debug/programming capability of ADuCM355

Evaluation capability with electrochemical gas sensors

ADT7420 0.5 C accurate temperature sensor via I2C

USB power option and connection to PC

图4.评估板EVAL-ADuCM355QSPZ外形图

图5.JP45和JP46连接ADuCM355 UART引脚到USB收发器

图6.LDO和电源周围跳线部分电路图

图7.HSTIA可编增益电阻

图8.用来RTIA2校准的HSDAC HSTIA和开关矩阵设定图

图9.用于RTIA2_03校准的HSDAC HSTIA和开关矩阵设定图

图10.用于RTIA2_05校准的HSDAC HSTIA和开关矩阵设定图