High or low human blood sugar levels may cause serious health threats, so monitoring blood sugar levels is the top priority. Currently, 150 million people worldwide suffer from diabetes, so there is a huge demand for personal portable blood glucose monitors (BGM).
The dynamic blood glucose monitor (CGM) shown in Figure 1 can help diabetic patients to check blood glucose readings in real time, and can also monitor blood glucose values over a long period of time. CGM can continuously monitor the blood glucose level, and then prompt the user when the user’s blood glucose level reaches a dangerous value. This monitor usually contains the sensor unit shown in Figure 2 and the aggregator unit shown in Figure 3.
Figure 1: Dynamic Glucose Monitor (CGM)
This sensor unit uses button batteries or coin batteries and is connected to the human body within a certain period of time (for example, 8 to 10 days). The aggregator unit is a battery-powered handheld unit that can use radio frequency (RF) technology such as near field communication to read blood glucose data. The battery management subsystem of the aggregator unit consists of a battery charger, a battery fuel gauge and a protector. A single 3.7 V lithium ion battery can run a general polymerizer unit. It can be charged via the USB or DC input of the power adapter.
Figure 2: CGM sensor unit
Figure 3: Schematic block diagram of CGM aggregator unit
The battery fuel gauge can predict and estimate the remaining capacity, state of charge, exhaustion time, and operating conditions of the battery under different load conditions, thereby helping to solve problems in battery management. Using the smart battery fuel gauge, users can extend the operating time (as shown in Figure 4) and battery cycle life. The Impedance Track™ measurement algorithm of Texas Instruments (TI) achieves battery capacity prediction with an accuracy of more than 99%, giving it excellent analog measurement performance and battery characteristic modeling capabilities.
Figure 4: The use of TI fuel gauge to achieve ultra-long running time
This blood glucose monitor provides a variety of single-cell battery measurement options, which is not only compact, cost-effective, and ultra-low power consumption. The fuel gauge can be mounted in the battery pack or on the system PCB, the latter being more common in portable medical applications.
Figures 5 and 6 show typical system-side and group-side fuel gauge configurations, respectively. The fuel gauge on the system PCB, such as BQ27426, only requires minimal user configuration and consumes very little current during normal operation. For higher levels of integration, some fuel gauges have integrated sense resistors, such as BQ27421-G1.
On the other hand, if the fuel gauge is mounted in the battery pack, a high-accuracy solution can be provided through flash-based firmware and a 256-bit integrated secure hash algorithm (such as BQ27Z561-R1). Protection integrated circuits such as BQ2970 can provide voltage, current and reverse charger protection.
Figure 5: Typical host/system side fuel gauge configuration
Figure 6: Typical battery pack side fuel gauge configuration
The battery fuel gauge improves the advanced and intelligent level of power management. Systems that do not have an accurate fuel gauge can only be shut down at a fixed voltage. When many devices are turned off, the system voltage is 3.5 V in order to protect the worst-case backup capacity (reserving power for shutdown), but as shown in Figure 4, only the battery voltage is measured by the microcontroller and the analog-to-digital converter, and then Generating a low battery warning is not a reliable way to measure remaining battery power. This is because most applications have variable loads. The battery fuel gauge will calculate the remaining power and change the shutdown voltage to meet the required reserve capacity requirements under any conditions, thereby increasing the operating time.
In addition to the advantage of maintaining a reserve capacity, some battery fuel gauges can also not report a 0% state of charge due to the high transient pulse load generated by the application, thereby reducing the battery voltage to below the terminal voltage. This feature is advantageous when the battery still has a high capacity, but high transient loads will cause the termination voltage to be reached early.
Batteries are complex electrochemical systems, which are affected by battery aging, temperature and impedance. Algorithms, compact equipment, and advanced equipment integration are all key features that improve system performance. What is the biggest challenge you face in medical battery-powered applications such as dynamic blood glucose monitors? Please tell us your views at the end of the article.