* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Extending battery life in smart locks
Induction motor wikipedia , lookup
Power over Ethernet wikipedia , lookup
Power inverter wikipedia , lookup
Three-phase electric power wikipedia , lookup
Pulse-width modulation wikipedia , lookup
History of electric power transmission wikipedia , lookup
Brushed DC electric motor wikipedia , lookup
Electric power system wikipedia , lookup
Audio power wikipedia , lookup
Stepper motor wikipedia , lookup
Electric battery wikipedia , lookup
Standby power wikipedia , lookup
Mains electricity wikipedia , lookup
Wireless power transfer wikipedia , lookup
Voltage optimisation wikipedia , lookup
Electrification wikipedia , lookup
Amtrak's 25 Hz traction power system wikipedia , lookup
Power engineering wikipedia , lookup
Distribution management system wikipedia , lookup
Power electronics wikipedia , lookup
Rechargeable battery wikipedia , lookup
Switched-mode power supply wikipedia , lookup
Variable-frequency drive wikipedia , lookup
Extending battery life in smart locks Chris Glaser Member Group Technical Staff, Applications Engineer Low Power DC/DC Texas Instruments Aramis P. Alvarez Applications Engineer Building Automation Texas Instruments New smart lock power architectures greatly increase battery life by reducing system standby power consumption. Power management is a key design challenge in every Internet of Things (IoT) and connected home product. If the consumer experiences product downtime due to dead batteries or gets tired of changing the batteries too frequently, they will likely choose to not use the product. This is especially true for smart locks. When a lock malfunctions, the result is frustration from being locked out of the office or hotel room. In addition to the relatively high peak current demands of the radio, common in all IoT applications, smart locks have an additional high peak current demand from the motor which turns the lock itself. Also, smart locks sit idle for the vast majority of every day—the time when they are actively locking or unlocking the door is very small. This combination of high peak current demands and very lengthy, low-power system standby time demands new power architectures to extend the battery life. System overview Wireless microcontroller While smart lock systems may contain many In a smart lock product, the wireless microcontroller integrated circuits (ICs) such as light-emitting diode (MCU) device communicates with the phone to ® (LED) drivers, Wi-Fi communications, and so on, lock and unlock the door wirelessly. In order to this paper focuses specifically on these three ICs: do this without any noticeable lag, the wireless microcontroller needs to be powered on to send an 1) microcontroller with wireless connectivity, such advertising event signal periodically, and then be put as Bluetooth® low energy; back into its standby state. Current consumption is 2) a motor driver; and much lower in standby—usually around the single- 3) power management. digit micro-amp (µA) range. Such a low current Throughout this paper, the term “events” refers to enables long battery life. the door locking or unlocking when the motor is Advertising events (not to be confused with the active. For example, locking the front door and then locking/unlocking events) occur when the wireless unlocking the front door counts as two separate microcontroller periodically wakes up to briefly events. Twenty-four events per day is commonly transmit identifying information and listen for used for comparing the performance of different incoming connection requests from peer devices smart locks. (e.g., a smart phone). The period of advertising events is programmable on most Bluetooth low energy devices from 20 ms to 10.24 seconds. Extending battery life in smart locks 2 November 2016 ure 1 6.1mA Advertising Event Advertising Event Advertising Event Advertising Event Advertising Event 1.2μA Figure 1. Current consumption versus time during a Bluetooth low energy advertising event. The longer the period, the longer it takes for a key. The current profile of the motor is different connection but the lower the power consumption. for each type of door lock, because the amount A period of 500 ms between advertising events of torque needed to turn the lock differs between is a good balance between power consumption different brands of door locks. On many locks, the and connection speed. Figure 1 shows the current through the motor ramps up and peaks at current consumption waveform of a typical around one amp. There are a number of sources of wireless microcontroller with Bluetooth low energy power dissipation in a motor driver, but the biggest communication [1] . Default values for the CC2640 source is the on-resistance of its MOSFETs. When current consumptions are shown in Figure 1. The choosing a motor driver, the highest efficiency is pie graphs and plots in Figure 6 and Figure 7 (see achieved with a very low on-resistance. The motor page 6) use the worst-case scenario of 9.1 mA of driver, such as a DRV8833, must work with the active current and 2.5 µA of standby current. These smart lock’s power source and the specific motor values are used for maximum output power. used. Considering both of these, the motor driver Since the advertising event period is programmable, voltage is typically around 5 V. the two most important values to look for when Power management choosing a Bluetooth low energy radio, in terms Power management is required to convert the of power consumption, are active (during an varying battery voltage to the voltages required advertising event) and standby currents. The supply by each of the loads: wireless microcontroller, voltage range of the SimpleLink™ Bluetooth low motor driver and any other sub-systems. Power energy CC2640 wireless MCU is 1.8 V to 3.8 V. In management adds cost, size and inefficiency to the this application note 2.5 V will be used to allow easy system. Thus, it is important to design the entire comparison between the different configurations. system with the power management in mind—the Motor power management must work together with All smart lock products need a motor and motor each sub-system. driver in order to turn the lock in either direction The power management’s efficiency is critical to the (lock and unlock) wirelessly and without a physical Extending battery life in smart locks performance of the overall system, especially in an 3 November 2016 IoT application such as a smart lock. This efficiency Any LDO converting 5 V to 2.5 V is 50 percent is important at the full system load with motor efficient at best, with much lower efficiency obtained turning and wireless microcontroller connecting, in standby-mode due to the LDO’s quiescent but critical when the system is in standby-mode— current (sometimes called ground current) [3]. For drawing micro amps (µA) of current. Being efficient example, the TPS76625 is suitable to convert at both light and heavy loads is challenging and four AA batteries to 2.5 V. This device achieves requires specially-designed ICs. 50 percent efficiency at higher loads, but only two The power management must ultimately run off of percent efficiency at the 1.2 µA standby load due to its 35-µA quiescent current. The very low efficiency the user-installed batteries. The choice of battery results in relatively high power consumption when type, number and configuration goes hand-in-hand the smart lock is in standby—this reduces battery with the system’s power architecture and power life. Figure 2 shows a typical block diagram of an management selection. AA-size alkaline batteries LDO-based system. are widely used in smart locks due to their wide availability to consumers and low cost. The average LDO full-load efficiency ηLDO1 = 50% per-cell voltage of an AA cell is around 1.25 V, AA though their voltage varies from under 1 V when fully 2.5 V Wireless Microcontroller AA discharged to 1.6 V when brand new. With four AA Power Management LDO 5V AA cells, over four years of battery life is achieved [2]. AA Whereas many existing smart locks focus on LDO standby efficiency ηLDO2 = 2% achieving lowest-cost power management with Motor Driver with Motor 4s1p low drop-out (LDO) linear regulators—at the expense of efficiency—newer, cost-effective power Motor driver efficiency ηMD = 100% management more than doubles the battery life with Figure 2. Smart lock block diagram using an LDO and four AA cells connected in series. minimal added cost. Switching DC/DC converters, both boost (sometimes called a step-up) and buck (sometimes called a step-down) converters, offer higher efficiency and a corresponding longer battery Boost converter life compared to LDO implementations. To overcome the LDO’s low efficiency in standby- Linear regulator mode, the battery configuration is rearranged and a boost converter is used instead. In this power The four AA batteries are connected as 4s1p (four architecture, the wireless MCU connects directly to series cells and one parallel cell) to create a 5-V the battery pack, which is arranged as a 2s2p (two supply voltage to power the motor. Now, only a series and two parallel cells). Since four cells are simple motor driver is needed to turn the motor still used, the cost and energy are the same as the on or off without any added power management. previous case. But since there are only two cells in Because of this, the motor sub-system operates at series, the total battery pack voltage is just 2.5 V—a nearly 100 percent efficiency. perfect match for the wireless MCU. Now, this LDOs step down the higher battery voltage to lower connection is 100 percent efficient. voltages. An LDO is used to convert the 5-V battery However, the motor still requires 5 V to operate. to the 2.5 V required by the wireless microcontroller. Extending battery life in smart locks From the 2.5-V battery, a boost converter must 4 November 2016 be used. A typical boost converter, such as the directly to the battery pack. Figure 4 shows a TPS61030, has around 85 percent efficiency when typical block diagram of a buck-based system. boosting to drive a motor. Due to the efficiency and A standard buck converter has a relatively large boost ratio (where the output voltage is greater than quiescent current (IQ). The high IQ dramatically the input voltage), the boost converter draws very decreases efficiency in standby-mode as it did high currents from the battery which increases the with the LDO [3]. However, the ultra-low power losses. Figure 3 shows a typical block diagram of a buck converter used in this example has ultra-low boost-based system. AA AA TPS62745, TPS627451 2.5 V IQ specifically designed for IoT applications, which have higher peak currents and long system standby times. Figure 5 shows that the ultra-low IQ enables www.ti.com Wireless over 67 percent efficiency at the typical standby- AA AA SLVSC68A – JUNE 2015 – REVISED JUNE 2015 Microcontroller 9.2.3 Application Curves Microcontroller with mode load currents with a 2.5-V output voltage. BLE efficiency ηBLE = 100% 2s2p 100 90 Power Management Boost 80 100 90 5V Motor Driver with Motor 80 70 Efficiency (%) Efficiency (%) 70 Boost full-load efficiency ηBoost = 85% 60 50 Figure 3. Smart lock block diagram using a boost converter and four 40 cells connected as 2s2p. AA V = 4.0V IN 30 20 10 system, a buck 10 0 1 100 1m 10m 100m Output Current (A) in place of theD001 converter is used LDO to dramatically increase the efficiency. At such as a TPS62745, is 90 percent 10m 100m D002 100 100 percent efficiency because it is connected 60 The 60 efficiency of the power architecture is critical efficient. The motor sub-system remains at nearly 80 70 Efficiency (%) 70 for extending the smart lock’s battery life. Power 50 Buck full-load efficiency ηBuck1 = 90% 40 30 Power Management Buck 2.5 V AA 20 5V 10 AA Buck standby efficiency ηBuck2 = 67% AA 0 1 4s1p 10 100 1m Output Current (A) 10m VIN = 3.6V management is necessary to convert the battery 40 VIN = 3.6V VIN = 4.0V Wireless VIN = 5.0V Microcontroller VIN = 6.0V VIN = 7.2V VIN = 8.4V VIN = 10.0V VIN = 6.0V 20 VIN = 7.2V consumes some of the battery’s energy to function. Figure 0 6 on the following page shows three pie 100m 1 10 100 1m 10m graphs of the power consumption of all three Output Current (A) D003 100m system blocks in a real smart lock for one day of Motor Driver with Motor D004 operation. The percentages Figure 9. show VOUT =how 1.5 Vmuch of the2.625 total system power budget is used for each Motor driver efficiency ηMD = 100% VIN = 3.6V of the three sub-systems, and the bar charts V = 4.0V 2.600 Figure 4. Smart lock block diagram using a buck converter and four 3.366 AA cells connected in series. IN show the total power consumption in each VVIN == 5.0V 6.0V 2.575 3.333 3.300 Extending battery life in smart locks 3.267 VIN = 8.4V VIN = 10.0V 10 Figure 8. VOUT = 1.8 V 3.399 VIN = 4.0V 30 to what is required by each sub-system, VIN = 5.0V voltage but it VIN = 4.0V VIN = 5.0V VIN = 6.0V 5 Output Voltage (V) 50 AA Efficiency (%) 100 1m Output Current (A) Power management architecture 90 80 comparison 90 Output Voltage (V) 10 Figure 5. An ultra-low power buck converter’s efficiency remains high, even at very light loads. Figure 7. VOUT = 2.5 V Figure 6. VOUT full = 3.3 V the buck the wireless microcontroller’s load, 100 converter, VIN = 3.6V VIN = 4.0V VIN = 5.0V VIN = 6.0V VIN = 7.2V VIN = 8.4V VIN = 10.0V 40 20 0 Taking the same power architecture as the LDO 1 50 30 VIN = 5.0V VIN = 6.0V VIN = 7.2V VIN = 8.4V VIN = 10.0V Buck converter 10 60 2.550 2.525 2.500 2.475 IN VIN = 7.2V VIN = 8.4V VIN = 10.0V November 2016 Daily power consumption with 24 lock/unlock events and ® 500-ms Bluetooth low energy advertising period Average Power in μW 900 Average Power in μW 900 LDO: 5 V to 2.5 V 800 Average Power in μW 900 800 800 Boost: 2.5 V to 5 V 700 600 Wireless MCU 29% 500 LDO 50% 600 600 300 200 100 Boost 39% Motor Driver 26% 100 0 Buck: 5 V to 2.5 V 500 Wireless MCU 35% 400 Motor Driver 21% 200 700 500 400 300 700 0 Buck 7% 400 300 Wireless MCU 53% 200 Motor Driver 40% 100 0 LDO Boost Buck Figure 6. Total and sub-system-level daily power consumption of the three power architectures. power architecture. A 500-ms advertising period Figure 7 compares all three power architectures and 24 lock/unlock events per day are used in with the number of lock/unlock events on the the calculations. For visual representation, the x axis and the number of years of battery life on overall size of each pie chart is proportional to the y axis. For many applications, which have less the total power used for each of the three power than 36 events per day, both the buck and boost management architectures—the bigger the pie architectures offer an improvement in battery life chart, the greater amount of power consumed. compared to the LDO architecture. For higher lock/ The height of each pie chart also shows the total unlock event systems, the buck architecture is still power consumption. best, but the boost architecture becomes worse than the LDO architecture due to the higher amount 9 of motor power required for more events. Lock/Unlock Events vs. Battery Life with 500-ms Advertising Period 8.5 Buck Boost LDO 8 Conclusion 7.5 New power architectures in connected devices, Battery Life in Years 7 6.5 such as smart locks, enable much higher 6 battery life compared to the current LDO-based 5.5 5 implementations. A switching power converter, 4.5 either a boost or buck, increases battery life for 4 3.5 smart locks with less than 36 lock/unlock events per 3 day. An ultra-low power buck converter more than 2.5 2 doubles the battery life for lower event systems, 1.5 0 4 8 12 16 20 24 28 32 36 40 44 48 while nearly doubling the battery life for higher event Number of Events Per Day Figure 7. Battery life versus power architecture and number of events per day. Extending battery life in smart locks systems. The ultra-low IQ of such a buck converter 6 November 2016 is critical to the battery life extension by vastly increasing the efficiency during the lengthy standby-modes of such systems. Designers of connected and IoT products should take another look at their power management architectures to make sure their products achieve optimal battery life. References 1. Joakim Lindh, Christin Lee, and Marie Hernes. Measuring Bluetooth Low Energy Consumption, Texas Instruments Application Report (SWRA478), December 2016 2. Smart Lock Reference Design Enabling 5+ Years Battery Life on 4× AA Batteries, TI Design (TIDA-00757) 3. Chris Glaser. IQ: What it is, what it isn’t, and how to use it, TI Application Note (SLYT412), 2Q11 4. Product folders: CC2640, DRV8833, TPS76625, TPS61030, TPS62745 Important Notice: The products and services of Texas Instruments Incorporated and its subsidiaries described herein are sold subject to TI’s standard terms and conditions of sale. Customers are advised to obtain the most current and complete information about TI products and services before placing orders. TI assumes no liability for applications assistance, customer’s applications or product designs, software performance, or infringement of patents. The publication of information regarding any other company’s products or services does not constitute TI’s approval, warranty or endorsement thereof. The platform bar and SimpleLink are trademarks of Texas Instruments. All other trademarks are the property of their respective owners. © 2016 Texas Instruments Incorporated SLYY107 IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest issue. Buyers should obtain the latest relevant information before placing orders and should verify that such information is current and complete. All semiconductor products (also referred to herein as “components”) are sold subject to TI’s terms and conditions of sale supplied at the time of order acknowledgment. TI warrants performance of its components to the specifications applicable at the time of sale, in accordance with the warranty in TI’s terms and conditions of sale of semiconductor products. Testing and other quality control techniques are used to the extent TI deems necessary to support this warranty. Except where mandated by applicable law, testing of all parameters of each component is not necessarily performed. TI assumes no liability for applications assistance or the design of Buyers’ products. Buyers are responsible for their products and applications using TI components. To minimize the risks associated with Buyers’ products and applications, Buyers should provide adequate design and operating safeguards. TI does not warrant or represent that any license, either express or implied, is granted under any patent right, copyright, mask work right, or other intellectual property right relating to any combination, machine, or process in which TI components or services are used. Information published by TI regarding third-party products or services does not constitute a license to use such products or services or a warranty or endorsement thereof. Use of such information may require a license from a third party under the patents or other intellectual property of the third party, or a license from TI under the patents or other intellectual property of TI. Reproduction of significant portions of TI information in TI data books or data sheets is permissible only if reproduction is without alteration and is accompanied by all associated warranties, conditions, limitations, and notices. TI is not responsible or liable for such altered documentation. Information of third parties may be subject to additional restrictions. Resale of TI components or services with statements different from or beyond the parameters stated by TI for that component or service voids all express and any implied warranties for the associated TI component or service and is an unfair and deceptive business practice. TI is not responsible or liable for any such statements. Buyer acknowledges and agrees that it is solely responsible for compliance with all legal, regulatory and safety-related requirements concerning its products, and any use of TI components in its applications, notwithstanding any applications-related information or support that may be provided by TI. Buyer represents and agrees that it has all the necessary expertise to create and implement safeguards which anticipate dangerous consequences of failures, monitor failures and their consequences, lessen the likelihood of failures that might cause harm and take appropriate remedial actions. Buyer will fully indemnify TI and its representatives against any damages arising out of the use of any TI components in safety-critical applications. In some cases, TI components may be promoted specifically to facilitate safety-related applications. With such components, TI’s goal is to help enable customers to design and create their own end-product solutions that meet applicable functional safety standards and requirements. Nonetheless, such components are subject to these terms. No TI components are authorized for use in FDA Class III (or similar life-critical medical equipment) unless authorized officers of the parties have executed a special agreement specifically governing such use. Only those TI components which TI has specifically designated as military grade or “enhanced plastic” are designed and intended for use in military/aerospace applications or environments. Buyer acknowledges and agrees that any military or aerospace use of TI components which have not been so designated is solely at the Buyer's risk, and that Buyer is solely responsible for compliance with all legal and regulatory requirements in connection with such use. TI has specifically designated certain components as meeting ISO/TS16949 requirements, mainly for automotive use. In any case of use of non-designated products, TI will not be responsible for any failure to meet ISO/TS16949. Products Applications Audio www.ti.com/audio Automotive and Transportation www.ti.com/automotive Amplifiers amplifier.ti.com Communications and Telecom www.ti.com/communications Data Converters dataconverter.ti.com Computers and Peripherals www.ti.com/computers DLP® Products www.dlp.com Consumer Electronics www.ti.com/consumer-apps DSP dsp.ti.com Energy and Lighting www.ti.com/energy Clocks and Timers www.ti.com/clocks Industrial www.ti.com/industrial Interface interface.ti.com Medical www.ti.com/medical Logic logic.ti.com Security www.ti.com/security Power Mgmt power.ti.com Space, Avionics and Defense www.ti.com/space-avionics-defense Microcontrollers microcontroller.ti.com Video and Imaging www.ti.com/video RFID www.ti-rfid.com OMAP Applications Processors www.ti.com/omap TI E2E Community e2e.ti.com Wireless Connectivity www.ti.com/wirelessconnectivity Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265 Copyright © 2016, Texas Instruments Incorporated