Bountiful power harvesting

The LTC3588-1 is an ultralow quiescent current power supply designed specifically for energy harvesting and/or low-current step-down applications. It can interface directly to a piezoelectric or alternative ac power source, rectify the voltage waveform, and store harvested energy on an external capacitor. It can also bleed off any excess power via an internal shunt regulator and maintain a regulated output voltage by means of a Nanopower high efficiency buck regulator.

The LTC3588-1's internal full-wave bridge rectifier is accessible via two differential inputs, P_Z1 and P_Z2, that rectify ac inputs. This rectified output is then stored on a capacitor at the V_IN pin and can be used as an energy reservoir for the buck converter. The low-loss bridge rectifier has a total voltage drop of about 400 mV with typical Piezo-generated currents, which are normally around 10 µA. This bridge is capable of carrying up to 50 mA of current. The buck regulator is enabled once there is sufficient voltage on V_IN to produce a regulated output.

The buck regulator uses a hysteretic voltage algorithm to control the output through internal feedback from the V_OUT sense pin. The buck converter charges an output capacitor through an inductor to a value slightly higher than the regulation point. It does this by ramping the inductor current to 260 mA through an internal PMOS switch and then ramping it down to 0 mA through an internal NMOS switch, thereby efficiently delivering energy to the output capacitor. Its hysteretic method of providing a regulated output reduces losses associated with FET switching and maintains an output at light loads. The buck converter delivers a minimum of 100 mA of average load current when it is switching.

With analog switchmode power supply design expertise in short supply around the globe, it has been difficult to design an effective energy harvesting system. However, the introduction of the LTC3108 and LTC3588-1 simplifies the process dramatically. High integration, including power management control and off-the-shelf external components, make them small, simple and easy-to-use to complete the energy harvesting chain.

Resources

Linear Technology Corp., www.linear.com