Get Longer Battery Life By Lowering Quiescent Current

March 13, 2017

Meng He  By: Meng He
 Executive Business Manager, Core Products Group, Maxim Integrated


Medical devices in the form factor of a patch can measure body temperature, monitor heart rate, and deliver insulin. The key to their efficacy is long battery life. The same goes for a host of other internet of things (IoT) devices, from smartphones and earbuds to video game controllers, electricity meters, and building automation systems. Many of these devices sit in storerooms for extended stretches before they’re put to use, or often, they have long periods of inactivity. For such small, battery-operated systems, it’s time to consider the role of low quiescent current in extending battery life.

Studies have revealed that a typical two-person household can have anywhere from 30 to 60 batteries in use in a variety of devices, each with its unique energy use patterns.1 Battery life is typically calculated based on the active, sleep, and hibernate currents of the central controlling unit, such as a microcontroller. Associated sensors and radios will also work together with the microcontroller. The power supply—typically consisting of switching or low-dropout (LDO) regulators and, sometimes, power management ICs (PMICs)—is critical in delivering energy to all of the system’s functional blocks. Active current consumption, of course, has a significant impact on battery life, but so, too, does standby current, particularly as sleep/hibernate functions consume larger portions of time in a device. During sleep/hibernate, the power supply’s quiescent current—the circuit’s quiet state—is actually the biggest contributor to a system’s standby power consumption. As an example, let’s take a system powered by a 40mAh, 1.55V silver-oxide coin-cell battery with a one-year shelf life. If the current drawn is about 4µA, reducing that current by a single microamp could increase the wearable shelf life by about three months.2 Although nominal, quiescent current can substantially impact a system’s power transfer efficiency during light load operation.

At a minimum, extending device battery life calls for designing with components such as low-power microcontrollers, sensors, radios, and efficient power supplies. Balancing battery capacity and size with efficient power management techniques is also essential, particularly as designs get smaller and lighter. Additionally, the right boost converter—DC-to-DC converters whose output voltage is greater than that of the source voltage—can extend battery life when the battery voltage drops to low levels. To ensure that you select the right boost converter for your battery-operated design, consider:

  • Quiescent current: the lower the better to preserve battery life at system standby mode
  • True shutdown mode: by blocking the current output from the input in shutdown, this capability improves efficiency and extends product shelf life
  • Input voltage range: allows running off of an almost “dead” battery
  • Efficiency: measured in VIN, VOUT, and IOUT, the higher the percentage, the better for increased battery life (>90% efficiency at uA level is ideal)

Today’s ultra-small designs clearly can benefit from circuits with low quiescent current and available in a small form factor. Mere nanoamperes of current flow would be ideal.

New Boost Converters with 300nA Quiescent Current

Maxim now offers a family of boost DC-to-DC converters that are ideal for battery-powered applications that need long battery life. These converters offer ultra-low quiescent current (300nA) and True Shutdown™ technology, where the output is disconnected from the input without forward or reverse current. The MAX17222 features a 0.5A peak inductor current limit. Output voltage can be selected using a single standard 1% resistor. The circuit is available in 0.88 x 1.4mm2 6-bump WLP and 6-pin uDFN packages and features 95% peak efficiency throughout the entire load range.

MAX17222 boost converterThe MAX17222 boost converter has only 300nA of quiescent current. 

Get a deeper understanding of how quiescent current impacts battery life by reading our white paper, Why Low Quiescent Current Matters for Longer Battery Life.  

Sources

1 http://blog.batterysharks.com/average-household-and-the-number-of-batteries/
2 Maxim Integrated. Meeting the Design Challenges of Wearable and IoT Devices. San Jose, 2017.