© janaka dharmasena dreamstime.com_technical Application Notes | December 20, 2017
Switching & Protecting Electronics in Battery-Powered Systems
Battery-powered electronics poses multiple challenges to the power system engineer. At a theoretical level, the battery related circuitry (before DC/DC conversion) may be divided into four functions: power selection, charging (for rechargeable batteries), monitoring and protection.
This is a product release announcement by Linear Technology (now part of Analog Devices). The issuer is solely responsible for its content.
Power selection prioritizes between the multiple power sources typically available in a battery-powered system, e.g., wall adapter, USB port and internal battery, whereas the charging circuit needs to be customized to the specific battery chemistry. Monitoring circuitry reports battery voltage, charge, and temperature status, which used alongside a battery protection circuit, ensures higher reliability. In this article, we will explore the features and benefits provided by a new micropower battery protection device, ideal for battery applications ranging from automotive, medical to consumer applications. Figure 1. A Possible Battery & Load Protection Discrete Circuit; Source: Hand-sketch above Considerations When Designing with Battery Power Even simple battery related problems, not just fires and explosions, can tarnish a product’s reputation. Therefore, attention needs to be paid to the design of battery related safety features. Batteries come with their charge and discharge current ratings; exceeding these ratings heats up the battery, which not only reduces the life of the battery but explodes it in the worst case. Overcurrent protection may be implemented with fuses, but fuses are bulky, slow to react and have wide tolerances in their trip threshold (Figure 1). To prevent irreparable damage, rechargeable batteries need to be disconnected before going into deep discharge. For a 3.7V Li-Ion cell, this level is around 2.5V. An undervoltage lockout (UVLO) circuit is needed to disconnect the battery from the load. This may be implemented with a comparator, reference voltage, and a solid-state switch. A P-channel MOSFET high-side switch doesn’t need a charge pump to turn it on, lowering battery current drain, but P-channel MOSFETs have limited selection and cost more than N-channel MOSFETs for the same on-resistance. Conversely, a more efficient N-channel MOSFET low-side switch may be used if the ground line can be floated. The undervoltage threshold needs to have sufficient hysteresis; otherwise, the UVLO circuit will oscillate off-on-off since battery voltage recovers after load turn-off. After battery protection, we need to consider load protection. Transient voltage suppressors implement overvoltage protection during brief conditions such as ringing, spikes and surges, but burn up during sustained or DC overvoltages (OV). Therefore, another comparator is needed to protect the load from an input overvoltage. If a battery is misinserted with reversed polarity, the load may be damaged if it cannot tolerate negative voltages. A series diode is used to block the negative voltage. But, this diode dissipates power and drops significant voltage during forward operation. As seen, a bunch of discrete components and circuits are needed to implement comprehensive protection for battery-powered systems. At the same time, the quiescent current consumption of these circuits needs to be kept low so that battery run- and standby-time is not shortened. For example, automotive electronic modules have a standby current budget of less than 100µA to prevent battery discharge while a car is parked for a few weeks. For high current dissipating circuits, a relay may be used to disconnect them from the battery. Relays are also used to turn the load on and off but relays are bulky, preventing form-factor reduction. A more efficient and simpler protection method is needed. Figure 2. LTC4231 Hot Swap Controller & Electronic Circuit Breaker Consumes Just 4µA of Quiescent Current, Ideal for Battery-Powered Systems; Source: PR photo, remove background and logo Low Quiescent Current Solution for Battery Power Control & Protection The LTC4231 is an ultralow quiescent current (IQ) hot swap controller, enabling safe insertion and extraction of boards or batteries in 2.7V to 36V systems (Figure 2). The 2.7V to 36V operating range accommodates a wide range of battery chemistries including lead-acid, Li-Ion, and stacked NiMH, NiCad or alkaline. The LTC4231 controls external low-loss N-channel MOSFETs to gently power up board capacitors, avoiding sparks, connector damage, and system glitches. Soft-start and inrush current level is easily adjusted with a resistor-capacitor connected to the MOSFET gate. During normal operation (pass MOSFETs fully on), dual level overcurrent protection is provided by a timed circuit breaker and fast current limit. For minor overloads, a fault timer is activated; when it expires, the MOSFETs are opened to disconnect the load. During heavy overloads or an output short-circuit, the fault timer is activated and load current is limited to 60% above the circuit breaker threshold. Depending on the option, the LTC4231 either stays off after an overcurrent fault or automatically turns on after a 500ms cool-down period. Undervoltage protection cuts off low voltage batteries to prevent deep discharge, while adjustable hysteresis avoids oscillations from battery recovery after load removal. Input overvoltage disconnects the load, preventing damage. The LTC4231 survives and also protects downstream circuitry from reversed batteries up to −40V by controlling back-to-back N-channel MOSFETs (Figure 3). A single MOSFET is sufficient if reverse input protection is not needed. Figure 3. When a reversed battery is inserted, e.g., −24V at IN, the LTC4231 protects the load by blocking the negative voltage from propagating to the output (OUT). Back-to-back MOSFETs (shown in Figure 2) are needed for reverse input protection.; Source: Figure 6 on page 14 of LTC4231 datasheet Even with all this functionality, device quiescent current is a mere 4µA during normal operation; placing the LTC4231 in shutdown mode reduces its IQ to 0.3μA and turns off the external N-channel power MOSFETs to disconnect downstream circuits, extending battery standby time. To ensure low current operation, the undervoltage and overvoltage resistive dividers are connected to a strobed ground, lowering their average current draw by 50x. Techniques to Lower Quiescent Current The LTC4231 employs two innovative techniques to lower its current consumption during normal operation while providing protection that is indistinguishable from other current-hungry controllers. To turn on the external N-channel MOSFETs and lower their on-resistance, the LTC4231 uses an internal charge pump to generate a gate voltage at least 10V above the input voltage. In other controllers, the charge pump works continuously even after the gate is driven on, essentially idling but contributing significantly to quiescent current consumption. In contrast, the LTC4231 turns off the charge pump after the MOSFET gate reaches its peak voltage. If the gate voltage sags due to leakage, the charge pump turns on to deliver a pulse of charge, refreshing the gate voltage. This is shown in Figure 4 for example gate leakages of 0.1µA and 1µA. Figure 4a. To lower quiescent current, LTC4231 activates the charge pump periodically to refresh the MOSFET gate voltage as needed. 4b. The MOSFET gate voltage refresh rate is shown for two different gate leakage examples (ΔVGATE is GATE-to-SOURCE voltage, ICC is LTC4231’s current consumption).; Source: a: Cut-out from Functional Diagram on page 8 of LTC4231 datasheet, delete line spurs and the two N-channel MOSFETs between GATE and SOURCE; Source: b: Figure 7 from page 15 of LTC4231 datasheet This technique reduces charge pump current consumption by a factor of 50x to 100x as the charge pump on current is 200µA but drops to 2µA in sleep mode. The second technique to lower LTC4231’s quiescent current is to sample the input voltage every 10ms to determine if it has gone below the undervoltage threshold or above the overvoltage threshold. A strobed ground connection (GNDSW) is provided for the external input voltage resistive divider (Figure 5). The occasional sampling lowers the resistive divider’s current consumption by 50x, which is the sampling period (10ms) divided by the sampling window (200µs). The comparators monitoring the UVL, UVH, and OV pins are turned on during the sampling window, lowering their average current consumption also by 50x. The 10ms sampling period works well for batteries since their voltage changes slowly over time. However, if the undervoltage or overvoltage condition occurs at start-up, the LTC4231 holds the MOSFETs off to block the out-of-range voltage from propagating to the load. Figure 5: The input voltage is monitored in a 200µs window every 10ms (2% duty cycle) to lower UV/OV monitoring current consumption by 50x. During the sampling window, GNDSW is connected to GND by an internal 80Ω switch.; Source: Cut-out from Functional Diagram on page 8 of LTC4231 datasheet, remove line spurs Conclusion Most emerging electronic applications—wireless sensors, fitness trackers, augmented reality glasses, drones, robots—are battery powered, for reasons of functionality, portability and convenience. Energy-dense batteries such as Li-Ion have brought the issue of battery safety into the public eye. The LTC4231 provides a simple, compact and rugged micropower solution for hot plugging and battery protection, especially in energy conscious applications, protecting the system against battery deep discharge, output overload or short-circuit, overvoltage and reverse battery connections.
Author: Pinkesh Sachdev, Product Marketing Engineer, Mixed Signal Products, © Linear Technology Corp. (now part of Analog Devices)
Author: Pinkesh Sachdev, Product Marketing Engineer, Mixed Signal Products, © Linear Technology Corp. (now part of Analog Devices)
Jenoptik is looking to accelerate growth with acquisition of TRIOPTICS Jenoptik is acquiring 100% of the shares in TRIOPTICS GmbH, a supplier of test equipment and manufacturing systems for optical components and sensors.
Global microelectronics market with overall stable development "Although the growth path of the global microelectronics market is intact, on a long-term trend-line, it declined by 12.1 percent to USD 412 billion in 2019," said Dr. Sven Baumann, ZVEI expert for microelectronics, sensors and actuators.
Jörg Doblaski takes on the role of X-FAB CTO X-FAB Silicon Foundries announced the appointment of Jörg Doblaski as its new Chief Technology Officer (CTO). He fills the role of former CTO Dr. Jens Kosch, who is becoming an X-FAB Fellow and will serve as an adviser to the company’s CEO Rudi De Winter.
GaN and SiC power semiconductor markets set to pass $1 billion mark in 2021 The emerging market for silicon carbide (SiC) and gallium nitride (GaN) power semiconductors is forecast to pass USD 1 billion in 2021, energised by demand from hybrid & electric vehicles, power supplies, and photovoltaic (PV) inverters.
POET and Sanan IC Inks LoI to form $50 million JV The proposed JV aims to disrupt the data center market using the POET Optical Interposer to achieve superior economics and scale.
SG Wireless designates Digi-Key as authorised distributor for the US SG Wireless, the IoT solutions arm of EMS provider Season Group, has added Digi-Key as an authorised distributor of its IoT products for the US.
Kioxia completes acquisition of LITE-ON Technology’s SSD business Kioxia Holdings Corporation says it expects to complete its acquisition of LITE-ON Technology Corporation’s Solid State Drive (SSD) business, Solid State Storage Technology Corporation and its affiliated companies on July 1, 2020.
II-VI licenses technology for SiC devices and modules for power electronic II‐VI Incorporated has singed an agreement with General Electric to license GE's technology to manufacture silicon carbide (SiC) devices and modules for power electronics.
Dialog Semi completes its acquisition of Adesto Dialog Semiconductor says it has completed the acquisition of Adesto Technologies Corporation (Adesto)), a provider of custom ICs and embedded systems for the IIoT market.
Changes in NAND Flash Prices to Be Limited in 3Q20 Despite the reduced demand for consumer electronics and smartphones as a result of the COVID-19 pandemic, the NAND Flash market showed a short supply in 1H20, thanks to the corresponding rising demand for cloud services and distance education, as well as increased inventory procurement by some clients concerned with a possible breakage in the supply chain.
USI breaks ground on its new Huizhou manufacturing facility The electronics designer and manufacturer is looking to reinforce its foundation in Southern China and is doing so by adding a new manufacturing facility in Huizhou (Guangzhou, China).
R&M opens U.S. production facility The 10,000-square-foot facility in Elkridge, Maryland aims to services U.S. East Coast, Southern and Midwestern customers with consulting, production, support, and rapid delivery.
Osram: Slight recovery after weak 3rd quarter expected Osram Licht AG expects for the fiscal year 2020 a comparable revenue decline of -15 to -19 percent (previously:-3 and +3 percent), an adjusted EBITDA margin of 3 to 6 percent (previously: 9 to 11 percent) and a negative free cash flow in the mid double digit to lower triple digit million range.
Taiwan edges South Korea as largest base for IC wafer capacity China capacity expansion forecast to push the country into second place in the regional rankings in 2022, trailing only Taiwan in size.
Siemens acquires UltraSoC Siemens has signed an agreement to acquire Cambridge, UK-based UltraSoC Technologies Ltd., a provider of instrumentation and analytics solutions that put intelligent monitoring, cybersecurity and functional safety capabilities into the core hardware of system-on-chip (SoC).
BMW and Mercedes-Benz halt cooperation in automated driving The BMW Group and Mercedes-Benz AG are putting their cooperation on development of next-generation technology for automated driving temporarily on hold.
Olympus to divest Imaging Business Olympus Corporation and Japan Industrial Partners, Inc. signed a memorandum of understanding to carveout Olympus’s Imaging business to a new company and subsequently transfer its shares to a fund managed, operated or otherwise handled by JIP.
Dialog ups its outlook for Q2 Dialog Semiconductor says it is increasing its Q2 2020 revenue outlook due to a stronger than expected demand for tablets and notebooks.
Odyssey opens first European repair facility in Nijmegen Odyssey Technical Solutions is opening a new repair facility on Novio Tech Campus in Nijmegen. The company is focused on the repair and service of equipment in Radio Frequency (RF), DC and microwaves.
NOR Flash ASP to potentially drop in 2H20 NOR Flash buyers found that their inventories were low and stepped up their procurement efforts as they anticipated the growing risk of COVID-19 causing disruptions in the supply chain.
Globalfoundries acquires Land in U.S. Globalfoundries has secured a purchase option agreement for approximately 66 acres of undeveloped land adjacent to its most advanced manufacturing facility, Fab 8, in Malta, N.Y., near the Luther Forest Technology Campus (LFTC).
GF and SkyWater team up on technology development GlobalFoundries and SkyWater Technology have signed a Memorandum of Understanding (MOU) to manufacture secure solutions for the U.S. defense industrial base and cooperate on development of emerging technologies.
EBV Elektronik to franchise Sequans in EMEA EBV Elektronik, an Avnet company, today announced that it will distribute the product portfolio of Sequans Communications S.A. in EMEA.
Volkswagen increases stake in QuantumScape The Volkswagen Group is increasing its stake in QuantumScape and making an additional investment of up to US$200 million in the US battery specialist.Load more news