To this end, TI has been continuously improving its products' Iq (quiescent current) performance. Quiescent current is the nominal (average) current used when the device is "on" in its minimum operating state, such as when an amplifier IC is turned on and ready to operate, but is not currently amplifying anything. Or, for example, in the no-load operating state of a power converter, the voltage reference, error amplifier, output divider, and protection circuitry within the power regulator all consume current. Unlike "shutdown current," quiescent current is always present during operation. It also differs from leakage current, which primarily refers to the current leaking from the pins.
Zou Peng, Product Marketing Manager of TI's Boost and Buck-Buck product lines, stated that in addition to extending the standby life of IoT devices, a lower IQ can also achieve a longer shelf-life experience. Shelf-life refers to the period during which a product is not yet released and is still stored in a warehouse. Because the product is connected to a power source, it is very likely to experience excessive discharge due to power leakage. As a result, the first thing users do upon receiving the product is not to turn it on immediately, but to charge it or replace the battery. A lower IQ can minimize the occurrence of this awkward situation.
How does TI reduce the Iq of its chips?
The benefits of a low IQ are obvious, but it also brings a series of design challenges. Zou Peng explained that TI mainly addresses these challenges through three aspects.
First, we continuously improve our manufacturing processes. By leveraging TI's powerful ultra-low leakage current processes and control topologies, we achieve even lower transistor leakage current.
Secondly, it involves developing novel circuit structures to achieve rapid response. For power supplies, especially DC-DC converters, response speed is a crucial performance indicator because they need to respond instantaneously to different loads. However, faster circuit response speeds also lead to greater power consumption. TI innovatively utilizes fast wake-up comparators and IQ feedback control to achieve rapid dynamic response without compromising low-power performance.
Third, it continues to maintain small size, both in terms of the chip itself and the overall system size. As more and more additional circuitry is added to achieve low-power circuitry, the chip area increases. TI's area reduction techniques for resistors and capacitors are highly effective in concentrating these features in space-constrained applications without compromising overall static power consumption.
In recent years, TI has been developing power management chips with lower IQ, all of which are clearly market-specific, reflecting TI's consistent development strategy. Yan Honghui, General Manager of TI's Boost and Buck-Buck product lines, stated that the TI team maintains excellent communication with industry customers from the early stages of product development, enabling them to create more targeted products that significantly address customer pain points based on common needs—the TPS61904 being a prime example.
TPS61094 – A low-Iq chip with supercapacitor management function
The application prospects of supercapacitors are promising.
Meters represent a significant market for IoT applications. Smart meters record consumption and then communicate with data centers or end customers to display and record these values. Powered by a main battery, smart meters need to support a lifespan of 10 to 20 years. Generally, for meters with wide coverage, the operational costs of battery replacements are extremely high and therefore need to be avoided. Furthermore, most meter operations occur under light loads, with high pulse current loads only required during data transmission.
Taking the popular NB-IoT technology as an example, the chart shows the current consumption over time under different NB-IoT operating modes. The peak current consumption is 310mA in data transmission mode, lasting 1.32s, and the load varies significantly across different operating modes. The average current consumption throughout the entire process is 30mA, lasting 80s.
Current and time consumption in NB-IoT operation mode
Therefore, selecting the right battery for a smart meter is often the most critical step, as it affects the meter's standby power consumption and power architecture. There are many types of batteries, each with completely different characteristics. However, generally speaking, batteries with higher storage density cannot support high-pulse applications, while high-pulse batteries often lack sufficient density and can only meet instantaneous requirements.
In the wireless metering market, the traditional approach is to use lithium SOCL2 batteries as the main battery. LiSOCL2, employing hybrid layer capacitor packaging technology, supports instantaneous high-pulse operation. However, HLC also has several drawbacks: First, the discharge current cannot be controlled, thus preventing operation at maximum capacity; second, its performance is poor at low temperatures, necessitating the selection of larger and more expensive HLC batteries; third, if a transient current cannot be met, it needs to be used in conjunction with the main battery, but this instantaneous high current can negatively impact the lifespan of the main battery.
Currently, the industry has proposed a better solution: to use supercapacitors to replace HLCs in order to cope with sudden responses during wireless transmission.
Besides supporting large peak loads, supercapacitors can also provide backup power during system power outages, and they are inexpensive with guaranteed production capacity and reliability. Therefore, supercapacitors are currently used in various applications, including meters, portable medical devices, and POS machines. For example, blood glucose meters often use button batteries, which have limited power capabilities, so customers need a supercapacitor to support high-load modes. Furthermore, supercapacitors may also be utilized in applications such as energy harvesting systems.
As shown in the table above, single-cell power supply, HLC, and supercapacitors each have their advantages, but the solution using supercapacitors is more cost-effective.
Supercapacitors require a range of power management functions.
The charging and discharging of supercapacitors requires a series of circuit management processes, including charging, discharging, and power path management, which increases the complexity of circuit design. The TPS61094 is a bidirectional buck-boost converter that integrates supercapacitor charging and discharging. It features high integration, requires only a few external passive components, and has an Iq of only 60nA. Its simple design better meets customer acceptance of supercapacitor solutions. Based on TI's simulations and actual user design results, and considering the cost of supercapacitors compared to HLCs, this solution can improve system standby time by 20%, reduce components by 50%, and significantly reduce system cost.
As shown in the figure, when the system power is on, the TPS61094 enters Buck_on mode: it turns on the bypass FET, providing a constant current of 500mA to the supercapacitor, and stops charging when the voltage across the supercapacitor reaches 2.5V. VSYS directly supplies power to VOUT. When a power outage causes VSYS to drop, the TPS61094 automatically enters Boost_on mode: it turns off the bypass FET and supplies power to VOUT using the charge stored in the supercapacitor.
Zou Peng summarized that the TPS61094 has three key advantages: high integration, high power density, and ultra-low Iq.
Compared to competing boost converters, the TPS61904 boasts a peak inductor current of 2A, twice that of its competitors. This meets the peak current requirements of various wireless technologies such as NB-IoT, Bluetooth, and W-Mbus.
Furthermore, Zou Peng stated that the supercapacitor's voltage is 2.7V when fully charged, but it can support a minimum discharge voltage of around 0.8V. Many users are accustomed to using two capacitors in series, then using an LDO to step down the voltage to power the system. Since the load MCU operates at 3.3V, the supercapacitor cannot be fully utilized. The TPS61094, however, uses a boost circuit, achieving a 3.3V output with only one supercapacitor. This allows for better utilization of the supercapacitor's energy, extending its lifespan and saving costs.
For backup power applications, response speed is a crucial metric. The TPS61094 optimizes transient performance by monitoring the dv/dt slope at the output and adjusting its regulation behavior at any given moment. This allows for rapid detection of output voltage drop while maintaining a low IQ.
Furthermore, since supercapacitors are very fragile, excessive voltage can lead to electrolyte decomposition or capacitor overheating. Therefore, charging must ensure high precision and reliability. The TPS61904 can achieve ±2% accuracy across the entire temperature range of -40℃ to 150℃. The charging output current can be set from 2.5mA to 600mA, and it has a protection system including output short-circuit protection and thermal shutdown protection.
More flexible mode settings
The TPS61094 can automatically manage the charging and discharging of supercapacitors without the need for external detection circuits or MCU control, thus offering higher reliability, lower power consumption, and greater ease of use.
However, Zou Peng also emphasized that the chip is configurable to meet the needs of users in different scenarios, and can also deal with the drawbacks of supercapacitor self-discharge.
In forced buck mode, the TPS61094 connects its output directly to the input, while the buck converter outputs a set constant current to charge the backup supercapacitor. The buck converter stops charging when the supercapacitor reaches a preset termination voltage. The buck converter resumes charging when the supercapacitor voltage drops below a set voltage of 75 mV.
In forced bypass mode, the TPS61094 turns on the bypass MOSFET, and the output voltage equals the input voltage. In this mode, the IQ of the TPS61094 is approximately 4nA.
In true shutdown mode, the TPS61094 can disconnect the load from the battery input pin and the supercapacitor pin.
In addition, the device supports a true shutdown mode, which completely disconnects the load from the input.
summary
In addition to the TPS61904, TI has launched a variety of supercapacitor management solutions to meet the needs of different power consumption and battery scenarios. Each solution has its advantages and disadvantages. For example, some solutions use discrete circuits to charge the supercapacitor and use the TPS61022 boost converter to boost the supercapacitor voltage to a higher system voltage when the grid is interrupted. The TPS61022 has a higher output current capability than the TPS61094 solution, but requires more external components.
Another option is a supercapacitor backup power reference design with current limiting and active battery balancing. It uses the TPS63802 buck/boost converter as the supercapacitor charger and regulator, eliminating the need for additional discrete charging circuitry. However, it still requires additional external components to implement power ORing, charging current limiting, and supercapacitor terminal voltage settings.
TI offers a variety of solutions for supercapacitor charge and discharge management.
Low IQ solutions for automobiles
A car that has been parked for a long time is difficult to start, mainly because many in-vehicle devices are not turned off when the car is not running, but remain in standby mode, causing the battery to drain completely. Therefore, ultra-low power standby is also very important for automotive power systems, as it can greatly improve the user experience. TI also uses low IQ technology in many automotive chips to extend the lifespan of the power supply.
For example, TI's newly launched LMR43620 and LM43620-Q1 are 3V to 36V, 2A synchronous buck regulators. Their Iq remains below 3μA at 150°C, and they achieve 85% efficiency under a light 1mA load. The LMR43620-Q1's optimized control architecture and function set enable an ultra-small solution size. This device uses peak current mode control, further reducing output capacitance. The LMR436x0-Q1 utilizes pseudo-random spread spectrum, a low-EMI HotRod package, and optimized pinout to further reduce the input filter size.
Another option is TI's low-Iq automotive-grade ideal diode, the LM74720, which achieves lower power consumption and lower cost compared to standard diodes or P-FETs, with an Iq of only 35μA. The LM74720-Q1 ideal diode controller can drive and control external back-to-back N-channel MOSFETs, thereby simulating an ideal diode rectifier with power path on/off control and overvoltage protection. This product features fast response characteristics, a powerful boost regulator with fast turn-on and turn-off comparators, and supports 200kHz active rectification, thus providing a high level of system protection.
Summarize
Standby IQ has long been an issue, but it has not received much attention, mainly because it is not as significant as other system losses or standby power consumption. However, with the increasing prevalence of battery-powered devices and the decreasing power consumption of processors and other components, the industry has gradually realized that extending battery life and shelf life is closely related to IQ.
TI's groundbreaking process and architecture design enable low Iq characteristics to be widely used in a variety of products, such as DC/DC converters, power switches, low dropout regulators (LDOs), monitors, ideal diodes and other power management system components, and are widely used in devices ranging from industrial instrumentation applications, automotive sensors and personal wearable devices.
