Low power consumption is of paramount importance in scenarios where uninterrupted use is required for maximum efficacy and minimum inconvenience as in medical devices, wearable or portable electronic products and internet-of-things (IoT) devices. Replacement of a battery in mid-use of a therapy session or data-acquisition period, for example, is not an option in such devices.
CSS has developed key design techniques incorporated within an application specific integrated circuit (ASIC), that enable us to maximize the use of battery charge by increasing the efficiency of the power delivery mechanism which is crucial to such devices. These devices typically require a switch-mode regulator such as a step-up or Boost/Flyback converter or step-down/Buck regulator. Step-up converters are used so that higher voltages than the battery can be attained for the operation of certain modes (neuro-stimulation, sensor operation, etc.). Step-down or Buck converters that provide voltages lower than that of the battery may be used to optimize the power consumption of the device. This is because many circuits only rely on the supply of a certain amount of current as long as the voltage itself is above a certain value. Using a linear or LDO regulator to create the lower voltage does not lower the power consumption as it only results in power loss across the regulator itself. For example, given a 3.6V battery that supplies 200 uA and a linear regulator output of 1.2V (to power circuits that can operate off 1.2V) means that the battery provides 720uW of power of which 480 uW is dissipated across the linear regulator. With only 240 uW finally delivered to the circuits, the linear regulator approach at best achieves an efficiency of 33%. A switch-mode regulator such as a Buck converter may hence offer a more efficient implementation. However, both step-up and step-down converters can themselves consume a large percentage of the energy budget, especially in applications where supply current usage is below 100 uA.
By using novel circuit techniques within the ASIC, power that is usually wasted in the voltage conversion process can actually be re-harnessed to sufficiently offset the operational current of the converters themselves. This is very important in low-current applications, since without such techniques, converter efficiency is usually very poor at low load currents as shown in the graph below for a Buck-converter. Devices that operate with currents below 20 uA have been successfully implemented using these techniques, thereby making them ideal for medical devices, wearable/portable electronics and the IoT arena.