Enhance the Battery Life of Your Mobile or Wireless Device


Get the tools you need to measure and analyze dynamic current drain from sub-microamps to amps to deliver exceptional battery life

As a growing number of electronic devices are designed to be portable and integrated with various features, battery runtime has emerged as a crucial differentiator between products and a critical factor in ensuring customer satisfaction.

This application note outlines the tools you need to measure and analyze dynamic current drain from sub-microamps to amps to deliver exceptional battery life.

Powering the Wireless Revolution

The success of the wireless revolution is visible in the number of devices we use daily: smartphones, tablets, e-readers, GPS units, wearable patient monitors, heart-rate monitors, and many more. Some attribute this success to the long-awaited convergence of highly integrated technology, wide bandwidths, application-rich content, and attractive pricing.

Of course, the insatiable demand for any time anywhere access leads to end-user expectations that increase pressure on product designers. For example, visit any product-review page, and one of the most significant issues—or opportunities—becomes apparent: battery life.

The power challenge stems from two shared issues. One is to use power from a battery or a low-power DC bus, and the other is long periods of standby operation between bursts of intense RF activity. The resulting current drain is pulsed with extremely high peak current, low duty cycle, and low average values. Accurately measuring the profile of dynamic current drain can be complex and challenging with many of today's existing tools.

Solving the Challenge

The old way: falling short

With today's million-to-one dynamic current ratios, typical solutions fall short in many ways, whether the tool-of-choice is a current probe and oscilloscope, a DMM, a shunt, or an SMU.

Current probe and scope

This is the simplest way to measure dynamic current waveforms. It offers a good measurement range, wide bandwidth, and time-correlation of events. However, there are three significant drawbacks: accuracy depends on the scope's resolution, dynamic range reaches down to just a few milliamps, and periodic zero compensation is needed. Also, this approach isn't suitable for long-term data collection because acquisition is not gap-free.

DMM with auto-ranging

The methods used in most DMMs can measure a wide range of current levels. However, because most DMMs are designed for low frequencies, they can't handle the pulsed currents in battery-powered devices. Also, because ranging can take several milliseconds, the DMM may miss part of the current waveform. Worse yet, the input impedance may change during auto-ranging —and this can make the device-under-test (DUT) lock up, reset, or shut down.

Precision shunts with a DMM

These offer good accuracy at any level and can be used to get milliamp-level readings. However, different shunts are required to measure different levels: resistance must be high for low currents and low for high currents. Furthermore, shunts can add a burden voltage that may affect the measurement results.

Conventional SMUs

These measurements into the picoamp range are perhaps the most accurate way to measure steady currents. However, coupling between the output source and measurement subsystem may cause changes in the output current limit—and glitches or voltage drops—during range changes that can interrupt tests and damage DUTs.

Custom shunt/digitizer solutions

Long-term current-drain profiles can provide a complete picture of device performance under varying operating conditions. This can be achieved by putting a shunt in series between the DUT and a power source and then connecting the shunt to a digitizer that transfers data to a PC for logging. This works well down to milliamp levels, but measurement offset errors and the large shunt resistance make it unusable when standby currents fall below 1 μA.

The new way: The Keysight N6781A and N6785A

To help you overcome these issues, Keysight Technologies, Inc. has created a purpose-built solution that provides high accuracy and flexible measurement capabilities. The N6781A and N6785A are two-quadrant SMU modules that plug into the N6705C DC power analyzer mainframe.

Serving as both a source (power supply) and measurement device, the N6781A and N6785A provide stable DC output voltage, programmable output resistance, and an auxiliary digital voltage meter (DVM). Coupling these features with those listed below, the N6781A and N6785A are today's ideal solutions.

Seamless measurement ranging

This patented capability lets you measure and visualize the current drain in new and informative ways. A single sweep provides accurate measurements that range from sub-microamps to amps. See page 6 for more info.

Current-only measurements (ammeter mode)

This mode lets you connect a battery to the DUT and then simultaneously log the current drain profile along with battery voltage values with no shunt burden voltage.

Fast response DC source

The N6781A and N6785A provide fast recovery times and glitch-free operation when powering dynamic loads. The absence of unexpected output glitches helps ensure the proper operation of the DUT.

Battery emulator mode

The source is programmable in terms of DC level and output resistance. This is another capability that helps to emulate a battery more accurately.

Precision constant current or constant voltage load

The ability to operate as a CC or CV load can be used to create battery charge and discharge profiles. This mode includes static and dynamic operations.

Arbitrary waveform generation

For stress testing, user-defined tests, and more, the N6781A and N6785A let you create custom DC power waveforms such as DC bias supply transients and disturbances. See page 14 for more info.


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