Energy collection is mainly seen as a power supply method for power supply to the electronic devices that need to be added to the power supply or other than the battery. In many cases, applications that use energy collections often have no sufficient space to accommodate large volumes. Typical examples include wearable technologies such as fitness gadgets and health monitoring devices, as well as wireless sensor nodes such as environmental or structural status monitoring applications.
Typically, the energy collected from environmental energy sources such as solar energy, vibration or temperature differences, needs to be effectively utilized after transition, boosting, and temporary storage. Nowadays, a number of companies launched by the energy collection apps and power management integrated circuits are increasingly increasing. But the pressure is facing, to ensure that these devices are highly integrated to facilitate multi-function operation, and the size should be as small as possible. There is no doubt that the power consumption of the equipment itself is very low.
This article will outline the miniaturization needs of rapidly wearable electronic equipment markets and their related applications, and discuss recently, BQ25570 boost charger with integrated buck converters, and a series of similar alternatives and complementary components. This article will refer to the user guide of TI, explain how to effectively use the device to ultracen low power, space / weight limit.
More features
Today, it is more increasingly wearable devices that track the fitness plan to monitor health status and provide health care conditions and provide medical services. As most portable devices, this trend will promote the increase in equipment functions with consumers expect. If the GPS device is integrated in the heart rate monitor, track the recording ring number or running route, the heart rate monitor will be more favored. Currently, modern wearable health monitoring equipment can monitor blood pressure, body temperature, blood oxygen content, heart rate and activity.
Figure 1: Energy collection will be key technologies in many wearable electronic device applications.
Left: Sensoria's smart socks, equipped with pressure sensors, can communicate with the foot rings via Bluetooth to help identify and improve running postures (heel / foot). Other sensors can track records, speed, consumption calories, heights, and distances.
Right: Fraunhofer Institute R & D The wearable auxiliary equipment for the elderly group can provide a series of programmable services such as taking drug reminders, health monitoring and emergency assistance calls.
Wireless connection makes it easy to transfer and store collected data for later analysis. Wireless sensor networks as part of the Internet of Things, is essential in applications such as intelligent buildings and environmental monitoring, and data from many sensors in these applications must be compiled. Because of this, integrated sensors, radio frequency circuits, and more precise microcontrollers increasingly in smart watch, biometric monitor, ID tag products, sensor nodes, and other wearable or remote applications.
However, such multi-function devices should be favored, except for reasonable battery life, it also requires light weight, small size and comfort. Designers have used energy collection techniques to effectively utilize environmental energy such as body heat or footsteps, so that the battery continues to charge. In certain devices (such as implanted devices), the collected energy is the only energy source.
Therefore, energy collection can be seen as a spatial practical technology that can be used alternative to battery, and can achieve a smaller volume of rechargeable battery. For any device that is powered by the battery or the energy supplied, power management is very important. To ensure optimum performance and high efficiency operations by high power consumption, usually irregular power supplies, requires certain accuracy and precision. A number of IC manufacturers have targeted this market, including Advanced Linear Devices, Cymbet, Linear Technology, Maxim Integrated, Spansion, StMicroelectronics, and Texas Instruments.
Compared to the old generation of power, the new generation of power supplies is higher, the volume is smaller, and the power consumption is lower. In theory, the device will get the resulting energy, and then conversion and / or boost, and finally supply it directly to the system or rechargeable energy storage device. Some designs can be dedicated to a type of energy storage device such as a supercapacitor or a lithium ion button. There are also other designs that support multiple energy storage devices. Similarly, some design may be dedicated to a form of energy collection, and there are other designs that support multiple forms of energy.
A focus to note is the startup voltage required for different applications. Some applications are started to 20 mV, but the functionality may be limited, and additional complementary components are required to provide sufficient power management. The components with higher integration may have a smaller size, and the overall static current is lower, but a higher start voltage may be required to make it more dependent on the lowest level of storage energy. Some devices are very targeted, dedicated to ultra-low power sensor nodes. Other devices will support higher input voltage levels to meet the requirements based on microcontroller equipment, but for energy collection applications, these micro devices themselves are very low.
It is important that the power management IC needs to be flexible enough to handle intermittent power and the energy collected (often unstable, and often collecting the amount). This must be considered in the system design, ie enough energy storage capacity, it is possible to provide constant electricity when needed. This depends to a large extent on the sensor's read frequency, and the transmission amount of the data and the transmission frequency.
High integration
Texas INSTRUMENTS offers a variety of ultra low power micro devices for energy collection applications, including power management ICs, wireless connections, and microcontrollers. The company's latest BQ25570 is a high integrated energy collection of a femto power management solution. It meets all the standards with energy collection techniques and all standards for power restricted applications.
The device is compact, using a 3.5 x 3.5 mm QFN package of 20 leads, ultra-low power static current is 488 NA (typical value), and the transport mode is. 1881.5 NA. In addition, there is also a BQ25570EVM evaluation module. For detailed products and application information, please refer to the equipment specification and evaluation board user guide 2.
The device still requires an external capacitor and resistor, but due to high integration, it can minimize the need for additional equipment. The apparatus is ideal for wireless sensor networks with harsh power and operational requirements, implementing high-energy pulse frequency modulation (PFM) boost charger and femto power buck converter solutions. See Figure 2 below:
The apparatus can be used in conjunction with a variety of high impedance energy, including photovoltaic (solar), thermoelectric generator (TEG), and AC / DC rectifier and piezoelectric generators. From the cold start state, the device's DC / DC boost converter / charger minimum voltage minimum is 330 mV. Its hypothesis is based on: the input power supply provides at least 5 μW (typical), and the load converter output is less than 1 μA leakage current (including the storage element leakage current). However, the boost converter output voltage reaches 1.8 V after running, and the 100 MV voltage required for the device can be obtained from the energy collection source.
The buck converter is first obtained from the boost converter output to obtain input power, and then performs a step-down process, and finally provides an adjustment voltage for the output pin. The buck converter uses PFM control to adjust the voltage to enable it close to the value set by the user programmable resistor voltage divider. The current through the inductor is controlled by the internal current detection circuit. From the time of delivery mode, the time is about 100 ms, from the standby mode starts faster, but this depends on the size of the output capacitor.
BQ25570 can be used with a variety of storage devices, including capacitors, supercapacitors, lithium ion batteries, and other chemical batteries. When the system is in low power or sleep mode, the collector will provide sufficient electrical energy to charge the storage element. When the energy collector is not working, the battery or capacitor must have sufficient power to power the entire system load. An equivalent capacitor 100 μF storage element is required to filter the pulse current of the PFM switching charger.
According to TI's user guide, the main difference between the battery and supercapacitor is that there are few in the battery, and even less than a certain amount of voltage, and there is a supercapacitor. System designers need to note that there is a significant leakage current, which is equivalent to a DC load on the boost converter output.
Maximum Power Point Tracking (MPPT) refers to the most powerful energy and management of the photovoltaic cell (70 to 80%) and TEG (50%). Other functions that the battery-powered equipment high energy efficiency management includes: battery overvoltage and undervoltage protection, automatic thermal shutdown of the rechargeable lithium ion battery. Accurate monitoring of battery status is another important feature. If the system may enter an undervoltage state, it is also necessary to trigger the load current drop function.
Alternative equipment and supplement equipment
The BQ25504 and BQ25505 functions launched by Ti are similar, but the quiescent current is less than 325 NA. Both devices are equipped with an autonomous power multi-purpose multiplexer gate driver, once started, allowing the system to obtain energy from energy collection sources and primary batteries, ensuring that constant power is provided when needed, even when the collector is not available It can also work properly. The ultra-low static current is very important when the system contains unable to turn off, so that the battery life can be extended.
If the size and weight are problem, TI recommends BQ25100, which is a linear battery charger with a lower power, particularly suitable for single lithium ion buttons. The device is encapsulated by 0.9 x 1.6 mm WCSP, supports up to 30 V input voltage, allowing the fast charging current to be accurately controlled within 10 mA to 250 mA.
The complementary equipment TPS82740A and TPS8274B buck converter modules support 200 mA output current, conversion efficiency is as high as 95%, the quiescent current consumed is only 360 NA, and 70 NA is 70 NA. The 6.7 mm2 package contains a switching regulator, an inductor, and an I / O capacitor. By integrating all the necessary passive devices, the volume of the device is 75% smaller than the same discrete solution. The TPS82740A is an ultra-low voltage application, and the TPS8274B has the "DCS Control" feature, which is suitable for power management, such as Ti, for, for example, Ti. MSP430 series.
in conclusion
To select a portable application of energy collection technology, select the appropriate power management IC, you need to carefully consider the power requirements of the system, energy generation potential and energy storage capacity. At low ends of the power range (such as wireless sensor nodes), or if the energy generated by the TEG is very small, the selection of the device is more limited. If small size and light weight are best priority, then select a higher integration, such as several of this article, perhaps the best solution.
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