ADuCM355: Precision Analog Microcontroller with Chemical Sensor Interface

The ADuCM355 is an on-chip system that controls and measures electrochemical sensors and biosensors. The ADuCM355 is an ultra low power, mixed-signal microcontroller based on the Arm® Cortex™-M3 processor. The device features current, voltage, and impedance measurement capability.

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Description

The ADuCM355 features a 16-bit, 400 kSPS, multichannel successive approximation register (SAR) analog-to-digital converter (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 different sensor types. The analog front end (AFE) also contains two low power amplifiers designed specifically for potentiostat capability to maintain a constant bias voltage to an external electrochemical sensor. The noninverting inputs of these two amplifiers are controlled by on-chip, dual output digital-to-analog converters (DACs). The analog outputs include a high speed DAC and output amplifier designed to generate an ac signal.

The ADC operates at conversion rates up to 400 kSPS with an input range of −0.9 V to +0.9 V. An input mux before the ADC allows the user to select an input channel for measurement. These input channels include three external current inputs, multiple external voltage inputs, and internal channels. The internal channels allow diagnostic measurements of the internal supply voltages, die temperature, and reference voltages.

Two of the three voltage DACs are dual output, 12-bit string DACs. 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 impedance measurements. The output frequency range of this DAC is up to 200 kHz.

A precision 1.82 V and 2.5 V on-chip reference source is available. The internal ADC and voltage DAC circuits use this on-chip reference source to ensure low drift performance for all peripherals.

The ADuCM355 integrates a 26 MHz Arm Cortex-M3 processor, which is a 32-bit reduced instruction set computer (RISC) machine The Arm Cortex-M3 processor also has a flexible multichannel direct memory access controller (DMA) supporting two independent serial peripheral interface (SPI) ports, universal asynchronous receiver/transmitter (UART), and I2C communication peripherals. The ADuCM355 has 128 kB of nonvolatile flash/EE memory and 64 kB of single random access memory (SRAM) integrated on-chip.

The digital processor subsystem is clocked from a 26 MHz on-chip oscillator. The oscillator is the source of the main digital die system clock. Optionally, a 26 MHz phase-locked loop (PLL) can be used as the digital system clock. This clock can be internally subdivided so that the processor operates at a lower frequency and saves power. A low power, internal 32 kHz oscillator is available and can clock the timers. The ADuCM355 includes three general-purpose timers, a wake-up timer (which can be used as a general-purpose timer), 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 power oscillator to clock a watchdog timer on the analog 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 as required in a specific application. These peripherals include UART, I2C, two SPI ports, and general-purpose input/output (GPIO) ports. The GPIOs, combined with the general-purpose timers, can be combined to generate a pulse-width modulation (PWM) type output.

Nonintrusive emulation and program download are supported via the serial wire debug port (SW-DP) interface.

The ADuCM355 operates from a 2.8 V to 3.6 V supply and is specified over a temperature range of −40°C to +85°C. The chip is packaged in a 72-lead, 6 mm × 5 mm land grid array (LGA) package.

Note that, throughout this data sheet, multifunction pins, such as P0.0/SPI0_CLK, are referred to either by the entire pin name or by a single function of the pin, for example, P0.0, when only that function is relevant.

Drawings/Packages

0719 ADuCM355 Drawings-Packages 1

0719 ADuCM355 Drawings-Packages 2

Key Features
Analog input/output

- 16-bit, 400 kSPS ADC
- Voltage, current, and impedance measurement capability
        - Internal and external current and voltage channels
        - Ultralow leakage switch matrix and input mux
        - Input buffers, PGA

Voltage DACs

- 2 dual output voltage DACs
        - Output range: 0.2 V to 2.4 V (±2.2 V voltage potential to sensor) for 12-bit outputs
- 2 bias potentiostat and TIA amplifiers
        - Ultra low power, 1 μA per amplifier
- 1 high speed 12-bit voltage DAC
        - Output range to sensor: −607 mV to +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 in the ±0.00005 μA to ±3000 μA range
        - Programmable load and gain resistors
- Analog hardware accelerators
        - Digital waveform generator (refer to the ADuCM355 Hardware Reference Manual)
        - DFT and digital filters
- 2.5 V and 1.82 V on-chip, precision voltage references

Internal temperature sensor, ±2°C accurate

- Impedance measurement range of <1 Ω to 10 MΩ, 0.016 Hz to 200,000 Hz

Voltammetry scan rate up to 2000 steps per second

Microcontroller

- 26 MHz Arm Cortex-M3 processor
- Serial wire port supports code download and debugging
- 128 kB flash/64 kB of SRAM

Security and safety

- Hardware cyclic redundancy check (CRC) with programmable polynomial generator (refer to the ADuCM355 Hardware Reference Manual)
- Read and write protection of user flash

On-chip peripherals

- UART, I2C, and SPI serial input/output
- Up to 17 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 section
- Hibernate with bias to external sensor: 8.5 μA
- Shutdown mode with no SRAM retention: 2 μA

Package and temperature range

- 6 mm × 5 mm, 72-lead LGA package
- Fully specified for −40°C to +85°C ambient operation

General Applications

- Gas detection
- Food quality
- Environmental sensing (air, water and soil)
- Blood glucose meters
- Life sciences and biosensing analysis
- Bioimpedance measurements
- General amperometry, voltammetry, and impedance spectroscopy functions

Evaluation Board

YES — The ADuCM355 can be evaluated with the EVAL-ADuCM355.

0719 ADuCM355 Evaluation Board

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