How Power Efficiency Enables Low-Cost Sensing for Remote Monitoring and Management (RMM)

By Tu Bui, Systems Applications Manager

There has been a huge increase in the number of sensors all around us gathering data on everything imaginable—such as temperature, moisture, motion, vibration, and light levels, to name just a few.

All these sensors need to be powered, of course, which can be far from easy. In remote monitoring and management (RMM) applications, we need sensors that eke out power from a battery for as long as possible. If the sensor is efficient enough, it can even be powered using energy harvesting, meaning there is no need to ever replace the battery.

In RMM, automotive, and IoT, design engineers are therefore looking for sensors that use the least possible power while also enabling compact, reliable solutions.

While there are many issues to consider, one of the most important is standby current. How much power does a sensor or other device use when it’s asleep or shut down, and how can this be minimized?

The Load Switch Solution

To reduce standby power usage, the best answer is often to isolate a sensor, other component, or sub-system when it’s not needed. This can be achieved with a load switch, which provides a flexible solution in a compact package.

A load switch is an electronic switch that is used to turn power on and off. An example is the AP2280 from Diodes Incorporated (Diodes) (Figure 1), which is based around a P-channel MOSFET. When the load switch is activated, using the EN pin, the MOSFET is turned on and current can then flow from the IN to the OUT pins.

Figure 1. AP2280 block diagram

Using a load switch to disconnect power and isolate sub-systems can also help improve safety and provide more flexibility in power sequencing and start-up/power-down operation.

Teaming Up: Load Switch and Converter

Let’s look at how a load switch works with a power converter to minimize losses. For example, the AP72250 from Diodes is a high-current, synchronous boost converter. It provides high efficiency across a wide 0.6V to 5.5V input voltage range, excellent transient response, and high output voltage up to 5.5V.

The AP72250 supports a 900kHz switching frequency with a 20µA quiescent current (IQ). This IQ current is already low enough for many applications, where the power source can handle the resulting losses.

However, by adding a load switch, we can do much better. In fact, by using the AP2280 load switch along with the AP72250, the quiescent current when idle can be as low as 4nA.

This minuscule IQ figure means that a much smaller or lower capacity battery still provides enough energy for the sensing circuitry—for example, a sensor could be powered for multiple years from just a coin cell.

As well as excellent power efficiency, the power system can be compact enough for wearable, IoT, and RMM applications: the AP72250 is supplied in a small footprint WLCSP-12 package, measuring 1.75mm x 1.35mm x 0.45mm, while the AP2280 is available in SOT25 and DFN2018-6 packages.

The combination of excellent efficiency and tiny size enables designers to create compact sensor systems with small, long-life batteries—thus reducing overall cost and minimizing long-term maintenance in the field.

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Posted in Technology, Tagged Analog Products, Boost Converters, Load Switches, Posted 18 days 以前 by , Tu Bui | Systems Applications Manager