[Introduction]This article will introduce a new class of DC-DC converters, one example of which is the LTC3336. It consumes only about 65 nA in standby mode, making it ideal for battery-powered systems.
Conversion efficiency is a key characteristic of power converters. Common switching regulators (buck converters) used for buck conversion typically have conversion efficiencies between 85% and 95%. The achievable efficiency is highly dependent on the available supply voltage, the corresponding output voltage to be generated, and the required load current. However, many applications require a special type 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 draw very low amounts of current in standby mode. Examples include sensors that measure bridge vibration or detect forest fires. In such cases, it is important to maintain a low battery discharge for a long time. This feature is especially important in systems that rely on energy harvesters as an energy source.
Such sensors are also usually connected to other devices by radio. Individual nodes, usually by means of energy harvesting or battery power, are linked to transmit signals across multiple nodes and over long distances. These individual radio nodes must always listen for signals in a kind of “sleep mode,” switching to a more energy-intensive operating mode and broadcasting the corresponding signal when the corresponding signal is present.
Figure 1. A system with a sensor that continuously powers the sensor with very little energy—for example, a sensor capable of detecting forest fires.
The LTC3336 represents a new class of DC-DC converters. It consumes only about 65 nA in standby mode when the output voltage is generated and there is a light load on the output. Figure 2 shows an example of a compact circuit that generates an output voltage of 2.5 V from a VIN of approximately 7 V.
Figure 2. LTC3336 Buck Converter Generates 2.5V Output Voltage With Only 65nA Quiescent Current
Such voltage converters typically have their output voltage not set through a resistive divider, which would waste too much energy. To be able to set different output voltages, use pins OUT0 to OUT3. Depending on the wiring of these pins, the output voltage can be set between 1.2 V and 5 V in steps.
In many energy harvesting applications, the energy source must be protected from excessive current loads. Some batteries or harvesters can only supply a limited amount of 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 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 proper wiring of the IPK0 and IPK1 pins.
Figure 3. Power conversion efficiency from 7.2 V to 2.5 V is about 70% even with a load current of only 1 µA
The efficiency curves in Figure 3 show the efficiencies that can be achieved at very low output currents, such as 1 µA. This saves a lot of energy, especially in long hours and low load applications.
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 circuits with a fixed battery size can work longer, or energy harvesters can be designed to be smaller and therefore less expensive.
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