Although quiescent current is usually insignificant, it is an important factor in managing battery life in wearable devices, with the proliferation of smart, small devices that make battery life the focus of attention.
What makes all the discussions and trends of wearables and the Internet of Things (IoT) possible? Medical patches that measure body temperature, deliver insulin, and monitor heart rate must work long hours reliably.
In addition, these devices are generally stored in storage rooms and medicine cabinets for a longer period of time before being used by the patient, and doctors and users must be confident that the batteries of their devices are in good working order in use. Similarly, smart watches, earbuds Headphones and video game controllers must be able to use longer periods of time between two charges (Figure 1).
Smart watch and earbuds Figure 1 is an example of a system where battery life is of paramount importance.
Does anyone want to keep charging or stop when needed? Imagine the awkward situation that must be stopped for charging during Triathlon.
In addition, devices such as meters, gas detectors and building automation systems, as well as a large number of field sensors, must be able to operate reliably in the field, all of which tend to operate continuously in the background without frequent charging and maintenance. Detecting wearable and environmental testing, almost all IoT devices rely on batteries, which must be reliable, long-term operation under all conditions, and in fact the issue of battery life has come to a head.
According to market research firm Global Industry Analysts (Global Industry Analysts) data, the current emerging wireless network era of increasingly popular mobile demand driven by the global market for portable battery-powered products will reach 865.4 billion US dollars by 2020. Ordinary two-family Of course, each device has its own unique energy usage pattern.We next review how battery life is calculated, and discuss why the quiescent current is very important.
Affect the system standby power consumption quiescent current is essential
After manufacturing is complete, many IoT node devices remain in the off mode and are typically stored on a shelf until sold out and turned on.These devices are in standby mode most of the life of the device, perform certain actions on a regular basis or transfer data To the cloud.For wearable fitness monitoring devices, users wear relatively short stretches of time during training, and in view of this, it is necessary to explore ways to save energy when the device is in passive mode.
The system designer calculates battery life based on the operation, sleep, and deep sleep currents of the central control components (such as a microcontroller), the associated sensors and radios, and also the microcontroller, and of course, the power supply powers all the functional circuits in the system , But also the operation of the power consumption is an important factor in extending battery life, but the operating time is ultimately affected by the amount of time consumed by various power modes.If the Hibernation and Deep Sleep functions take up more time, each The standby current of the component is crucial.
In this case, the quiescent current of the power supply is the most important factor that affects the standby power consumption of the system, for example, assuming a system powered by a 40mAh, 1.55V silver oxide coin cell battery has a shelf life of one year (Figure 2 shows the button Button battery.) If the sink current is about 4μA, reducing this current by 1 μA extends the shelf life of the wearable device by about three months.
The coin cell in Figure 2 powers portable devices that need long-term operation.
Power supplies typically include regulators such as step-up or step-down regulators, or low dropout (LDO) regulators. Some power supplies also have power management ICs (PMICs) that involve a variety of power configurations and may even have battery charging Device.
Different from the quiescent current shutdown current can not wake up at any time
When the power supply is in standby mode, power dissipation is determined by the quiescent current (IQ), which is the quiescent state of the circuit, at which time no load is driven and the input is not switched. The quiescent current, although negligible, substantially affects the system's lightness Power transmission efficiency under load conditions.
Sometimes it is easy to confuse the quiescent current with the shutdown current. Quiescent current, the system is idle, but can wake up and take action at any time, which is usually the user wants the device state; the other hand, the shutdown current, the device is in hibernation status.
The designer uses the quiescent current to evaluate the power consumption of the power supply at light loads and uses the shutdown current to calculate the battery life when the device is powered down and the battery is connected to the regulator.
Designed to extend device battery life with low-power controllers, sensors, radios, and high-efficiency power supplies, design techniques such as advanced node CMOS manufacturing processes also help reduce the overall power consumption of the product, which in turn effectively extends battery life. The division chose to use boost converters to extend battery life when the battery voltage drops to a lower level.
However, this method can actually result in higher quiescent current and faster battery drain if the converter selected is not correct, and the end product specification is another important consideration. Consumers, and designers are forced to choose the more Smaller, lighter and lighter products.The difficulty is that the battery of the device is usually the largest and heaviest component on the device's circuit board.Of course, the smaller the size of the battery, the smaller its capacity, which is related to the longer battery life requirements Is contradictory.So designers must weigh the relationship between battery capacity and size and effective power management techniques.Improve system power efficiency is a common way to extend battery life.
Tight attention to the quiescent current pointer of a power regulator such as a boost converter is significant, and the lower the current, the longer the battery life.Therefore, there is a need to provide both lower quiescent current and smaller size than currently available products on the market Technology, especially for today's ultra-small form factor designs, where even currents as low as milliampere are not enough to affect battery life.Nowadays, wearable, mobility and IoT designs require as low as Nano-amp Current.
The boost converter is a DC-DC converter with an output voltage higher than the source voltage. Looking at the boost converter market, the VIN (5V) boost power management circuit is the fastest growing based on industry analysis data (Figure 3) Converter market turnover forecast.) Based on the IoT applications driving this growth, designers are looking for boost converters that provide lower voltage rails, longer battery life, and smaller solution sizes.
Figure 3 boost converter global turnover forecast
Benefit from nanoampere current ultra-small size / networking design touchdowns
Proper selection of boost converters that effectively extend battery life requires careful attention to a few key conditions, including quiescent current - the lower the current, the longer the battery life of the system in standby mode. This feature increases efficiency and extends the shelf life of the final product, saving expensive external components as an integral part of the converter; the input voltage range allows for the use of an almost depleted battery Operation; Efficiency - Measuring VIN, VOUT, and IOUT, the higher the percentage, the better the battery life (better than 90% at μA).
It is also important to understand vendors' performance in the field of power management technologies. Trusted vendors have a long history of providing advanced technologies to customers of all sizes and industries and continue to enhance their expertise and products over time. Some vendors are also Customers provide on-line simulation tools to evaluate efficiency curves and bill of materials (BOM) costs based on their design guidelines, enabling rapid prototyping of various sizes if an evaluation system and evaluation board are available. In addition, Size-sensitive design is also crucial.
Maxim now offers a DC-DC boost converter with ultra-low quiescent current (300nA) and True Shutdown technology ideal for battery-operated applications that require long battery life The MAX17222 nanoPower boost regulator features a 0.5A Peak Inductor Current Limit (Figure 4). The device incorporates a true shutdown technique that provides no forward or reverse current when the output is disconnected from the input. The output voltage can be selected from a 1% standard resistor. The MAX17222 features Transient Protection (ETP), allowing the output to remain within regulation within an input voltage down to 400mV, depending on the load current. The boost converter is available in a 0.88 × 1.4mm2, 6-bump wafer-level package and 6-pin uDFN package, peak efficiency of up to 95%, to minimize heat dissipation.
Figure 4 nanoPower boost converter block diagram
When looking for ways to extend battery life in future designs, the effect of quiescent current can not be ignored. Understanding the power characteristics of the final product in advance is very important, and this will be an effort toward directionality. When considering the components to be used, Low quiescent current combined with true shutdown, low input voltage range, and high efficiency at μA levels, helping to design intelligent, networked products that deliver long working hours per charge .