At present, one of the major trends driving the growth of portable and wireless medical devices is patient care, which is specifically the gradual use of telemonitoring systems in patients' homes. The root cause of this development is essentially the result of Economic considerations because it is simply prohibitively expensive to allow patients to be hospitalized for observation and treatment and as a result many of these portable electronic monitoring systems must incorporate RF transmitters so that any data collected from the patient can be directed back directly Pass the monitoring system of the hospital for future review and analysis by the competent physician.
In the face of the above scenario, it is reasonable to assume that the cost of providing a suitable home medical device to a patient is far less than the cost of getting the patient out of the hospital, but the most important point is that the device to be used by the patient must have Reliable, and easy-to-use features, manufacturers and designers of these products must ensure that they can run seamlessly on multiple power supplies and provide high reliability in wirelessly transmitting data collected from patients This requires designers to ensure that the power management architecture is robust, flexible, small and efficient.
Switching regulator high efficiency
For many applications in medical electronic systems, continuous powering is required even in the event of an interruption in the AC power supply, so one of the key requirements is to achieve low quiescent current to extend battery life. Thus, since 2010, power IC manufacturing Vendors have been making switching regulators with standby quiescent current less than 30μA. In fact, some of Linear's recently introduced products have reduced this to only 2.5μA, so these products are fully equipped with the backup power provided by the battery The conditions of use in the medical system.
Although switching regulators produce more noise than linear regulators, their efficiency guidelines are far superior to the latter, and it has been demonstrated that in many sensitive applications, as long as the switching power supply operates in a predictable manner, Noise and EMI levels are controllable. If the switching regulator performs switching at a fixed frequency in normal mode and the switching pulse edges are clean and predictable, there is no overshoot or high-frequency ringing, and the EMI can be minimized . Small package size and high operating frequency can provide a slim layout, thereby minimizing EMI radiation. In addition, if the regulator can be used in conjunction with low-ESR ceramic capacitors, then you can minimize input and output Voltage ripples, and these ripples are additional sources of noise in the system.
Many feature-rich patient monitoring medical devices, the increasing number of power rails, while the operating voltage continues to decline.However, many of these systems still need 1.xV to 8.xV wide voltage range for the motor, Low-power sensors, memory, microcontroller core, I / O and logic circuitry.
Traditionally, these rails have been provided by either a step-down switching regulator or a low-dropout regulator. However, for those configurations that also include a backup battery in the system to handle mains failure conditions, such ICs have not So that when the buck-boost converter (which can boost or reduce the voltage), it will be able to make full use of the battery range, which increases the operating margin and extends the battery run time, Because more battery life is available, especially when it is near the lower end of its discharge curve.
Medical DC / DC high requirements
In contrast, DC / DC converter solutions used in portable medical instrumentation that may also come with a main battery should have the following features:
A buck-boost DC / DC architecture with a wide input voltage range to regulate VOUT when using multiple battery-powered sources and their associated voltage ranges
2. Ultra-low quiescent current in both operating mode and shutdown mode to extend battery run time
3. Can effectively supply the system voltage rail
4. Current limit function to reduce the inrush current to protect the battery
5. Solution Small footprint, light weight, flat shape
6. Advanced packaging available to improve thermal and space efficiency
The new power IC that meets these requirements is the LTC3119 from Linear Technology. It is a synchronous current-mode single crystal buck-boost converter that provides up to 5A continuous output from multiple input sources in buck mode Current input sources include single or multiple cells, unregulated AC adapter, and solar panels and supercapacitors. Once started, this component can be expanded to 250mV from 2.5V to 18V input voltage range. Inputs above, At or equal to the output, the output voltage is stable and the output voltage is programmable from 0.8V to 18V. The user selectable burst mode operation reduces the quiescent current to only 31μA, Improve light load efficiency, and increase battery run-time. The LTC3119's proprietary 4-switch PWM buck-boost topology offers low-noise, jitter-free switching in all operating modes making it ideal for noise-sensitive power supply applications and Precision analog applications. In addition, the module also includes programmable maximum power point control (MPPC) function to ensure maximum power from a high output impedance power supply such as photovoltaic cells. Learn simplified schematic of the assembly.
Figure 1 High degree of integration and high performance LTC3119 peripheral circuits and efficiency.
The LTC3119 includes four internal low RDSON N-channel MOSFETs providing up to 95% efficiency. Burst mode operation can be disabled to provide continuous low-noise switching. External frequency programming or synchronization with an internal PLL allows for a wide range of 400kHz to 2MHz switching frequency range, thus allowing a trade-off between conversion efficiency and solution size Other features include short circuit protection, thermal overload protection, shutdown current below 3μA and a power good indicator. The external components, which operate over a wide voltage range and are packaged in tiny packages with low quiescent current, are ideal for RF power supplies, high current pulsed load applications, system backup power supplies, and even lead-acid batteries connected to a 12V conversion system.
Many portable medical systems require multiple input sources, including single or multiple cell configurations, AC adapters, and super capacitor banks.
Big opportunities have arisen in the design of many battery-powered or battery backed medical systems, while system designers face tough challenges in choosing the right power conversion solution to meet key design goals , These design goals include compliance with input-to-output voltage coverage limits, proper power levels, and ease of design without compromising efficiency, uptime, and meeting radiation regulatory requirements and solution size.
Designing a solution that meets system goals without compromising performance is a daunting task.Fortily, there are more and more Buck-Boost converter solutions that operate efficiently over a wide range of loads, This simplifies design, offers best-in-class performance, and maximizes uptime between battery charging cycles.