Why You Should Care About Quiescent Current

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From medical patches to smartwatches, earbuds, video game controllers, and more, the number of portable, battery-operated devices in our lives is growing. Similarly, more industrial devices like electricity meters, gas detectors, and building automation systems also must maintain reliable field uptime. In short, most internet of things (IoT) devices must perform reliably over extended periods—through stretches of inactivity and even after they’ve been sitting in storerooms or on shelves.

Most consumers appreciate not having to constantly charge mobile devices like earbuds.

Consumers expect their smart, connected devices to continue to get smaller while still delivering rich functionality and high performance. Longer battery life is a key to making this happen, and low quiescent current is an essential factor in extending battery life.

Calculating Battery Life

Battery life is typically calculated based on a few key factors: active, sleep, and hibernate currents of the central controlling unit, such as a microcontroller. Working together with the microcontroller are related sensors and radios. Another key component is the power supply, which delivers energy to each of the system’s functional blocks. Generally, power supplies include switching regulators that boost up or buck down the voltage or low-dropout (LDO) regulators. Power management ICs (PMICs) may also be included.

Battery runtime is ultimately influenced by the amount of time the device spends in each power mode. In standby mode, power consumption is defined by quiescent current (IQ), the circuit’s quiet state when it isn’t driving any load and its inputs aren’t cycling. While nominal, quiescent current can pose a substantial impact on a system’s power transfer efficiency during light load operation. In fact, when the device is in sleep or hibernation mode, the power supply’s quiescent current becomes the biggest contributor to the system’s standby power consumption. Consider, for example, a system powered by a 40mAh, 1.55V silver-oxide coin-cell battery with a one-year shelf life. If we assume that the current drawn is about 4µA, we could increase the wearable shelf life by about three months by reducing the current by a single microamp.1

The end product’s form factor is an important consideration when it comes to battery life. As our smart, connected things get smaller and lighter (while requiring longer battery life), this trend clashes with the fact that a device’s battery is often the largest, heaviest component on the board. How do you balance capacity and size with efficient power management techniques? Lowering the quiescent current of the power supply along with the design’s load circuits and other supporting parts is one avenue toward extending battery life.

Today’s ultra-small designs, in particular, could benefit from technology that provides lower quiescent current and a small form factor. In fact, even currents measuring in the milliamps may not be low enough to positively impact battery life. The sweet spot for IoT, wearable, and mobile designs may just be mere nanoamps of current flow.

Learn More

Want to learn more about why quiescent current is an essential consideration in extending battery life? Sign up for a copy of our white paper, which explains how you can improve battery life for your smart, connected products.

Sources

Maxim Integrated. Meeting the Design Challenges of Wearable and IoT Devices. San Jose, 2017.


By Meng He, Executive Business Manager, and Steve Logan, Executive Business Manager, Core Products Group, Maxim Integrated

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