“If you have an Electronic device that will not be used for a long time (such as a wireless headset, wearable device or remote control, etc.), you may find that it is not turned on and the battery is dead. If the device is just in standby or sleep, it may be due to a small but crucial factor, quiescent current.
“
If you have an electronic device that will not be used for a long time (such as a wireless headset, wearable device or remote control, etc.), you may find that it is not turned on and the battery is dead. If the device is just in standby or sleep, it may be due to a small but crucial factor, quiescent current.
What is quiescent current?
Quiescent current is defined as “current consumption when the device is inactive or in a sleep state”. Therefore, quiescent current (IQ) is the current drawn by the system in standby mode with light or no load. Quiescent current is often confused with shutdown current, which is the current drawn when the device is turned off but the battery is still connected to the system. However, both specifications are important in any low-battery design.
Quiescent current is a concern for most integrated circuits (ICs), where amplifiers, boost and buck converters, and low dropout linear regulators (LDOs) play a significant role in the quiescent current consumed. Among them, LDO is the product with the simplest design, and the power consumption is also easy to calculate.
For example, if you need to use an LDO 200mA output current with 0.05mA quiescent current, the Voltage drop drops from 4.2V to 1.8V, then the power dissipation is given by the formula:
When the application switches to standby mode or enters a light load state, the quiescent current as a percentage of power consumption increases significantly, for example if IOUT is reduced to, for example, 100 µA, the total power consumption becomes:
In this example, quiescent current contributes almost 50% of the power dissipation.
You might be thinking, “That’s not a huge waste of power.” But what about devices that spend most of their time in standby or off mode? Such as smart watches, fitness trackers and even some modules on mobile phones are often in non-working state. In order to achieve higher standby times in fitness trackers, the Display system cannot be kept running all the time. In such light-load applications, the power consumption of the LDO will significantly affect the overall battery life.
TPS7A02 Addresses Dual Space and Battery Life Constraints
Consumer electronics have been trending toward smaller and lighter weight, and engineers are challenged to reduce device size while extending battery life. In most cases, the battery is the largest and heaviest part of the design. However, designers don’t want to actually shrink the battery because that would reduce battery capacity and system life, so all other devices must be made as small as possible.
In order to achieve a smaller size, TI’s new LDO TPS7A02 has high peak power efficiency and small size, it is packaged in a 0.65 mm x 0.65 mm DSBGA with a pitch of 0.35 mm and can provide 25 nA of quiescent current. Not only is this one of the smallest LDOs in size, it is one of the lowest IQ devices on the market. The TPS7A02 also supports a small outline leadless (X2SON) package of 1mm x 1mm for designers who do not require the ultra-small size of 0.65mm x 0.65mm. The device offers the best of both worlds in size and performance.
Shibin Wang, product line manager of Texas Instruments (TI) battery management systems, introduced the key features and advantages of the TPS7A02, including:
・Extended application runtime and system life: The ultra-low IQ control of the TPS7A02 at light loads allows engineers to at least double the life of batteries using standard battery chemistries such as Li-Ion. For example, using the TPS7A02 in the design of wireless video doorbells and monitors, engineers can achieve battery life of 24 months or more (up to four times the industry standard). In addition, the TPS7A02 with a lower shutdown IQ of 3 nA can extend battery storage time in portable medical and wearable applications by up to five times compared to similar devices in the industry.
・Faster wake-up speed and better dynamic performance: For load transients from 1 to 50 mA, the TPS7A02 can respond within 5 μs, which is only half of the transient response time of similar devices in the industry, allowing engineers to design response times Shorter, better dynamic applications. The TPS7A02’s fast response to rapidly changing loads while providing smaller output voltage changes is beneficial for high-precision, low-power applications such as wireless Internet of Things (IoT) and portable medical devices that require noise-free current for accurate Acquire the signal around the device.
・Smaller solution and faster time to market: The TPS7A02 automatically transitions from IQ power saving mode, low load state, to high load, fast transient state without any external circuitry or components. As a result, engineers can use the TPS7A02 to reduce solution size by 70 percent and add more functionality in space-constrained applications, or reduce system cost with a smaller board.
Detailed explanation of TPS7A02 application scenarios
Pins that are enabled or disabled are a very simple solution if you want to design a system that saves battery life. Smartwatches, fitness trackers, phones and even drones can use this solution to boost their battery. For example, a drone spends very little time in standby mode, because the drone is usually only idle before or after a flight, and you can save battery life by turning off the LDO on modules not related to flight. The same is true for CMOS image sensor and gimbal applications, as these modules are only used when the user wants to record video or take pictures. The shutdown current of the LDO is usually a few hundred nA, and then the quiescent current is “drawn” from the battery, which can be lower than the quiescent current of the LDO, and by turning off the LDO, it can give the user more usage time.
Another reason LDOs are particularly well suited for CMOS image sensors and gimbal is that both systems are sensitive to noise, and any noise entering the image sensor or gimbal can affect the quality of video or pictures captured by the drone. Resolution and stability.
The idea also applies to a phone’s camera, which, while infrequently used, still needs a clean, noise-free power rail to maintain image quality.
Figure 1: Generic block diagram of a drone module, including processors, speed controllers, CMOS image sensors, stabilizers, etc., all require an LDO with an Enable pin to achieve the lowest standby power consumption.
Although battery life is highly dependent on load conditions during operation, an LDO with low IQ is also a must to help extend the runtime of any battery-operated device. These small devices are not limited to consumer electronics. They also play an important role in industrial applications such as construction equipment and factory automation. Designers sometimes ignore quiescent and shutdown currents, which results in additional power consumption that will be incurred for days to come, affecting the overall device experience.
So it’s time for engineers to focus on quiescent current, but also on overall power efficiency at the system level, using the TPS7A02 with other low quiescent current devices such as TI’s ultra-low power MSP430™ microcontroller (MCU) family, SimpleLink™ CC2642R MCU, TLV8802 nano-scale operational amplifier and TMP1075 low-power temperature sensor, etc., engineers can further optimize the battery life and performance in the system.
