Programmable analog IC delivers FPGA versatility to mixed-signal circuit designs
Designing, evaluating and debugging mixed-signal circuits with analog input/output interfaces has always been a major challenge for engineers. The task is even more difficult for an engineer whose background is primarily in the digital realm and is perhaps unfamiliar with analog design where issues of component selection, physical layout and power budget can greatly affect the circuit schematic and time to market. On top of this, engineering teams may also need to address another challenge: the development of hardware variants to support multiple versions of an end product. A core motor controller, for example, may need to feature I/Os that are tailored to a family of motors, each offering different current/voltage ranges, performance specifications or drive requirements.
However, there now exists an alternative approach to analog and mixed signal circuits, which can overcome the burden of designing and debugging multiple hardware versions. Although such speed and simplicity inherently imply a lack of flexibility, inadequate I/O and software indeterminism, Maxim Integrated offers a programmable analog IC that addresses these limitations by bringing the virtues and versatility of an FPGA-like device to the mixed-signal world.
Maxim’s MAX11300 PIXITM is a new programmable high-voltage mixed-signal IC that works in partnership with a microcontroller and is optimized for I/O requirements. The IC (see figure 1) features both, a 12-bit multichannel ADC and a 12-bit multichannel buffered DAC; and connected to these are 20 mixed-signal, high-voltage, bipolar ports. Each port is configurable as an ADC analog input, DAC analog output, general-purpose input/output port (GPIO) or an analog switch terminal. The device also features an internal sensor to track junction temperature and two external sensors to monitor environmental temperatures.
Fig. 1 – The MAX11300 is the industry's first configurable high-voltage mixed-signal I/O device that allows user-defined ADC, DAC or GPIO functionality
Click here to enlarge the image
Ideally suited for applications that demand a mixture of analog and digital functions, the MAX11300 runs independently following power-up configuration by a host microcontroller with each port individually configurable from a choice of four selectable voltage ranges from –10V to +10V.
There is of course an alternative approach, which is to use a microcontroller with embedded analog I/O and perform tasks in software. However, a MAX11300 based solution offloads the processor and its software, and also guarantees deterministic I/O performance that is unaffected by microcontroller priorities or interrupts. Essentially, performance will not be dependent on a specific configuration or the operating code of the microcontroller. In addition, many microcontrollers do not feature an integrated DAC. These are just the first of many advantages, including: high levels of flexibility, given that any of its 20 ports can be programmed as required, whereas these are fixed in a microcontroller; and versatility, in that each I/O port is selectable for 0 to 2.5V, ±5V, 0 to +10V, and -10V to 0V ranges, again not offered by a microcontroller. In addition, each pin can sink/source up to ±25mA, which is often required for direct connection to many real-world interfaces. The MAX11300 can also be used as a complementary unit for digital-logic devices, boosting system performance rather than impeding it.
A further important advantage of the MAX11300 is ease of use – programming or coding skills are not required with the device’s configuration software. Configuring the device is even straightforward for digital engineers that are unfamiliar with analog or feel more at home with FPGAs and programmable logic devices. The Maxim PIXI GUI delivers a familiar and easy-to-use drag-and-drop environment that makes programming easy and intuitive; it creates a script file that is loaded into the device on each start-up, as there is no memory in the device.
Programmable analog applications
The MAX11300 is well suited for mixed-signal circuits and applications that demand moderate resolution and speed. The list can include RF power-device bias controllers in telecommunications base stations, or in power-supply monitoring and sequencing, and in a wide range of industrial control and automation applications. To take just one application example from many, the device’s flexibility and versatility can be demonstrated in temperature control of a PWM fan-motor controller (see figure 2).
Fig. 2 – Typical control and monitoring application example based around the MAX11300
Click here to enlarge the image
The core of the control function is the closed-loop path from the temperature sensor to motor-control DAC with high-level supervision by a microcontroller. The MAX11300 can be configured for extra channels, for example, if advanced fan-motor controller requires the monitoring of additional analog inputs such as coolant flow, actuators and valves. This hardware-based implementation means that once established upon start-up – and functioning in parallel with the system microcontroller – analog functions become fixed and are deterministic in execution.
The analog-rich functionality of PIXI allows designers the flexibility to choose a main processor or microcontroller that is modest in features – in terms of performance or I/O or cost – and does not need to become a complete software-based analog front-end device. The solution can also mean significant flexibility in development as changes to design requirements can be implemented without a board redesign. Design and development risks can be reduced, so engineers can be more confident about schedule and performance, resulting in a faster time to market.
Also, compared to a more traditional discrete analog approach, use of a single IC reduces the Bill of Materials (BOM), while also supporting multiple end-product variations. The board layout will remain unchanged even with changes in analog-channel configuration. Design risk is further reduced because there is no need for analog-circuit expertise or issue in component selection.
To help engineers evaluate the possibilities of the IC, multiple hardware and support options exist today. A PIXI evaluation kit (see figure 3) provides a proven platform to evaluate the MAX11300. It is a complete board that can be interfaced to the PC via USB and includes a Windows compatible GUI to enable the programming and testing of all the capabilities of the IC. In addition, PIXI is also available as a peripheral module, enabling the simple prototyping of designs, by providing an IC with any system that uses Pmod-compatible expansion ports.
Fig. 3 – MAX11300 evaluation kit board
Although, traditionally, the terms analog and programmable have represented two very different realities, the MAX11300 provides a solution to this apparent paradox. It offers an enviable price/performance/size balance, delivering flexibility in I/O and interface functions while also providing predictable independent performance in parallel with a host microcontroller. For many applications, it can be the ideal complement to digital logic, which takes an array of gates and allows configuration to meet specific functional application requirements. Overall, the MAX11300 delivers: flexibility in terms of configurable I/O; versatility with every I/O having a true-bipolar high-voltage capability with selectable input ranges; and easy programmability via its intuitive GUI. In essence, PIXI is an FPGA-like device that makes analog design easy and represents a valuable solution for a wide range of applications in various markets.
Click here for German version.