The development of portable medical electronics has reduced healthcare costs. Battery-powered non-invasive sensors are mobile, and with on-board memory, they capture the complete data pattern for a condition. Due to the continuous advancement of IC technology, these devices are getting smaller and smaller and lasting longer, making them easier to adopt in this field.
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After the patient leaves the hospital, life often returns to normal. On weekdays, they should follow their doctors to protect their bodies, such as relaxing their mood, improving their heart rate, strengthening their nutrition, and so on. But no matter what the situation, people always have the limit. A simple patient monitoring device can be a win-win solution for patients and health care providers. It not only reduces the number of times patients go to the hospital, but also greatly increases the value of each visit.
Just a few years ago, the size of the sensor was too large to be used for continuous monitoring day and night; but with the advancement of electronic technology, its size has shrunk and the working time of a single battery has been extended. Blood glucose monitors and syringes are among the first successful applications, and the latest developments are closed-loop testing and insulin management equipment. These devices are now used throughout the day for Class I diabetic patients, but the concept should not be limited to diabetes.
In the past five years, small battery technology has changed little. The power supply design techniques and advances in IC technology directly contribute to the extended working life of these sensors. These advances realized with the mobile phone standard include: USB charging, high-efficiency DC/DC regulators, adoption of I/O standards (I2C, SPI, SDIO, etc.), and improvements in display technology.
One of the most important issues in the healthcare industry is when products can be delivered to patients. Project design cycles are generally very long and often span several years. Although not all of the time is spent in the electrical design phase, many times the electrical design team is often smaller in the company's internal team, and the chemical, legal, and testing teams are much larger. A key trend in electronics is to reduce time to market while reducing risk. All portable products require some form of power supply, typically powered by a primary or rechargeable battery. The battery's power must be adjusted to meet the needs of downstream complex sensors. This design extends battery life and enables the feature set to be used independently.
In the past, this power conditioning module consumed resources and actual operating power, taking up board space. Today, for DC/DC applications, the era of placing multiple MOSFETs around a simple switching PWM is gone, eliminating the need for numerous passive components to add minimal protection. We are talking about integrated DC/DC step-down ICs that have been used over the past five years. Currently, the electronics industry is rapidly evolving, including the active development of single-chip power modules. These devices, unlike the DC/DC modules in the higher-powered telecommunications industry, are true molded package ICs with a specific part number that can be supplied through a large number of sales channels.
Integration of DC/DC modules to increase efficiency and reduce risk Fairchild's FAN4603 uModule is such an IC. The principle is shown in Figure 1.
Figure 1 Fairchild's FAN4603 uModule
The basic controller with integrated FET is packaged in a single module with the input/output capacitors and the switching inductors required for the DC/DC buck topology. Its early advantages are very obvious, such as: size reduction, only one inventory component, the design cycle is correspondingly shortened. In addition, there are some technical advantages.
Because all active components in a single module are so close, high current and high frequency paths are reduced, reducing EMI, and for the medical device industry, which requires complex sensors and body interfaces, low EMI is a critical specification. By increasing the buck topology switching frequency of this module to 6MHz, it is possible to integrate stacked inductors. Due to the increased switching frequency, the inductor size is reduced. Because these passive components such as inductors and capacitors are chosen by the actual PWM and FET designers, the specifications are fine-tuned to provide ideal interoperability within the recommended load range.
The disadvantage of this adjustment is that the output voltage of the module is fixed, however the variable output voltage in turn leads to a matching imbalance of the passive components. Thus, different modules with a certain output voltage can be provided to solve the problem. The module that was first introduced has an output voltage of 1.8V and a Vin of 2.3 to 5.5V. This voltage range is ideal for single rechargeable batteries, AA and AAA dual battery packs, and a single 3V lithium-ion battery.
Another important advancement in the electronics industry driven by the need for portable medical device design is the increased efficiency of power modules on different loads. Medical application devices are often dormant, consuming very little power when the sensor is unbiased and does not collect actual data. During this time, the system Icc can be reduced to below 10 mA. Under these light and medium load conditions, PFM technology can be used to minimize losses inside the module. Figure 2 shows the typical efficiency curve of FAN4603.
Figure 2 Typical efficiency curve of FAN4603
Please note that its rated efficiency range is 70% to 85%, depending on the input voltage, only 1mA on the logarithmic X-axis. This curve is critical for battery life when the application range is between 10 mA and 200 mA, such as during data acquisition or RF communication with the base station.
Downstream Smart FET Technology Simplifies Power Allocation To better distribute the power of the power module to downstream sensors, processors, and LCDs, the use of point-of-load power switches is becoming popular in the industry. It is not new to use a simple P-channel FET to transmit power itself. The FET is surrounded by a number of diodes and transistors to add features such as load discharge, inrush current limiting, and reverse current blocking (RCB), which are some of the features. Clearly, the trend is to move to true smart FETs that integrate these functions in a single IC. Fairchild's IntellimaxTM family of products is one of the smart FET families available to designers. Its outstanding feature is the integration of all of the following features, overvoltage protection (OVP), overcurrent protection (OCP), RCB, and voltage. Slew rate control and error flags used to notify the processor of a failure. Figure 3 shows the internal schematic of a typical IntelliMAX device and the package used.
Figure 3 Internal schematic and package of a typical IntelliMAX device
A major advantage of medical applications is the ability to limit the power of external sensors and connectors when not in use. When the power of the sensor or connector exceeds the recommended level, the smart FET can isolate the power supply and issue an error flag to the processor. This increases the reliability of the terminal application, reduces its frequency of field failures, and ultimately reduces overall system cost.
The development of signal path technology for further energy savings and interoperability In addition to the significant increase in DC/DC efficiency previously discussed, general-purpose small-signal technology has also advanced, bringing more value to medical device applications. Analog switches are very common IC products that have limited use in the past and are mainly used to multiplex or isolate low-speed data lines. New features integrated in the switch now enable better on-resistance and flatness, power-down protection, higher data rates, and much lower power consumption. Understanding these features and their different strengths is the key to getting the most out of your medical device.
In the past, the on-resistance was only a static value, and the updated Ron flatness parameter ensured that the Ron value was within a certain range for a given condition. It can be used for calibration and sensor multiplexing in medical devices requiring Ron levels below 400mΩ, which is a significant improvement over the previous 8Ω level. The sensor's complementary feature has a recently introduced power-down protection feature that displays an input signal when Vcc = 0V. This feature is beneficial for hot-swappable applications of connectors and sensors. The actual operating current is now very low, even if the control voltage is lower than Vcc, the measured data is in μA (microamperes). Input-to-output leakage is as small as nA (nano), which further extends battery life. When the current medical device is upgraded to an updated feature set, these analog switches and inherent add-on functions are often used to increase the interconnect without having to replace the DSP and perform a lot of recalibration work.
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