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Ventilator design solutions from Maxim Integrated

Our supplier partners Maxim Integrated have worked with us to highlight how the components they provide play an important role in the design of Ventilator devices. The block diagram highlights some of the important features of a ventilator design.

Accurate sensing and timely control is paramount in ventilator devices – the core purpose of a ventilator device is to support patients breathing. It does this by ensuring an adequate ventilation rate is maintained for sufficient gaseous exchange to occur at the alveoli in the lungs, to oxygenate the blood and remove carbon dioxide.

Several factors must be monitored to decide the control parameters for the machine. These include the tidal volume – the volume of air exchanged during one breath, and the breathing rate – measured in breaths per minute. To maintain safe operation other factors must also be measured including the pressure of incoming oxygen and air supplies, as well as the state of control valves to ensure that there has been no mechanical malfunction of the device.

It is also common to have a separate safety controller which ensures the device is operating within defined safe parameters and overriding the main controller’s operation to fail-safe in the event of a fault condition being detected.

Maxim Integrated Ventilator Reference Design - Block Diagram

Sensing

It is important to ensure the air being delivered to the patient is of a suitable temperature and humidity, such that it will not dry out the lungs and provides optimum conditions for gaseous exchange. Temperature monitoring can be carried out using several approaches. A thermocouple device may be used in conjunction with an instrumentation amplifier such as the MAX4208 (189-8832) . Maxim also offer highly integrated devices specialised to this application, the MAX31856 (190-5444) precision thermocouple to digital converter with linearization.

For direct body temperature monitoring the MAX3020x series of devices offer a solution for high-precision body temperature monitoring, development kits are available which enable you to evaluate this sensor on a flex-PCB (193-8422) .

Actuation and Control

Controlling the ratio of air and oxygenpressure and duration of the ventilation cycle, requires the control of mechanical valves and actuators. For actuators requiring analog control DACs will be required to convert the digital control signals. Maxim provide a wide range of DAC devices from 8 to 18-bit resolution and in 1 to 32 channel packages.

Power

For battery-powered devices it is useful to measure the current consumption in real-time, of the full system or of sub-systems to detect common failure modes. The MAX9634 (190-6625) current sense amplifier provides high accuracy and low quiescent current consumption in an ultra-small package. An alternative is to utilise a battery fuel gauge device which employs coulomb counting to accurately determine the charge level of rechargeable cells. The MAX1720x series of devices implement the Maxim ModelGauge™ m5 algorithm and are available in single-cell MAX17201G+ (190-8162) and multi-cell variants MAX17216.

A well-regulated power source is essential for ensuring reliable performance of a ventilation device over many years. Unstable power sources may impact the performance of the machine and therefore patient welfare, as well as damaging other components in the system impact the lifetime of the machine. Maxim’s range of DC-DC converters are available for a variety of input and output voltage ranges.

User Interface

You may wish to include a flexible audio alert system in your design such that you are not limited to audible buzzers to alert medical staff of a system malfunction. The Maxim MAX9718 (189-8901) 1.4W differential audio power amplifier would be a low-cost solution for this application.

If your machine features any form of logging or wireless connectivity you may wish to consider the inclusion of an RTC to enable the timestamping of system logs, this will make it far easier to identify any patterns in system behaviour and diagnose faults. The Maxim DS3231MZ+ (778-1484) is a popular choice and is available in a variety of evaluation format (191-4210) .

Security

It is extremely important to have a method of identifying medical devices and verifying their authenticity. For basic device identity, serial number devices such as the DS28CM00 (190-5630) provide a unique identifier for each machine. If there are concerns of counterfeit devices being placed on the market you may wish to consider more sophisticated device identity schemes. Secure authentication ICs are available which employ ECDSA public key-based schemes. These devices can withstand even physical attacks and are increasingly being used to prevent the cloning of medical tools and sensors, the Maxim DS28 series (168-2876) provide varying crypto engines and interfaces.

Obsolescence

Obsolescence is an important consideration in medical device design. Medical certifications and approvals are often time-consuming and costly, so it is common to manufacture the same design for a product over many years. It is therefore important to select a supplier and manufacturer who can continue to provide the parts required to produce your design over many years. Maxim have a highly regarded obsolescence policy – whereby they rarely discontinue products where there is still a market demand.

Are you involved in medical device design and manufacture?

Let us know in the comments if you are involved in the response to the COVID-19 response in medical ventilator design.

Lead Inspiration Engineer @ RS Components and DesignSpark

24 Apr 2020, 8:53