Would you like to know more about this DC/DC converter that consumes only about 65 nA of current in standby mode?

Conversion efficiency is a key characteristic of power converters. Common switching regulators for step-down conversion (buck converters) typically have conversion efficiencies between 85% and 95%. The achievable efficiency depends largely on the available supply voltage, the corresponding output voltage to be generated, and the required load current. However, many applications require special types of conversion efficiency, for which there are special switching regulator solutions. These deployments require converters optimized for low output power. Always-on, battery-powered systems typically need to consume very low amounts of current in standby mode. Examples include sensors that measure vibrations on bridges or detect forest fires. In such cases, it is important to maintain a low charge discharge for a long period of time. This feature is particularly important in systems that rely on energy harvesters as an energy source.

Such sensors are also typically connected to other devices via radio. Individual nodes, usually powered by energy harvesting or batteries, are linked together to transmit signals across multiple nodes and long distances. These individual radio nodes must always listen for signals in a "sleep mode," and when the appropriate signal appears, it switches to a more energy-intensive operating mode and broadcasts the appropriate signal.

Figure 1. A system with sensors where low energy is required to continuously power the sensors – for example, sensors that can detect forest fires.

The LTC3336 represents a new class of DC-DC converters. It consumes only about 65 nA in standby mode when generating an output voltage and when there is a light load on the output. Figure 2 shows a compact circuit example that generates a 2.5 V output voltage from a VIN of about 7 V.

Figure 2. The LTC3336 step-down converter generates a 2.5V output voltage with only 65nA of quiescent current.

The output voltage of this type of voltage converter is usually not set by means of a resistor divider, as this would waste too much energy. To be able to set different output voltages, pins OUT0 to OUT3 are used. Depending on how these pins are wired, the output voltage can be set in steps between 1.2 V and 5 V.

In many energy harvesting applications, the energy source must be protected from excessive current loads. Some batteries or harvesters can only provide a limited current. If this specific current limit is exceeded, the voltage will drop, or in some cases, even damage will occur. Therefore, it makes sense to limit the current consumption of the power converter. The LTC3336 can limit the input current in adjustable steps from 10 mA to 300 mA. This input current limit is similar to the output voltage in that it can be set by appropriate wiring of the IPK0 and IPK1 pins.

Figure 3. Even with a load current of only 1 µA, the power conversion efficiency from 7.2 V to 2.5 V is approximately 70%.

The efficiency curve in Figure 3 shows the efficiency that can be achieved at very low output currents, such as 1 µA. This saves a lot of energy, especially in applications with long operating hours and low loads.

This article shows that the LTC3336 consumes only 65 nA in standby mode, making it an excellent choice for battery-powered systems. This means that a circuit with a fixed battery size can operate longer, or the energy harvester can be designed to be smaller and therefore less expensive.