User's Manual

USER MANUAL 1.34

STM 300 / STM 300C / STM 300U

Energy source

e.g. solar panel

Charge switcher

Overvoltage

protection

STM 300

Vdd

VDDLIM

CCO

Undervoltage

protection

RC delay

Short term storage

Long term storage

4 APPLICATIONS INFORMATION

4.1 How to connect an energy harvester and energy storage

STM 300 is designed for use with an external energy harvester and energy storage.

In order to support a fast start-up and long term operation with no energy supply available

usually two different storages are used. The small storage fills quickly and allows a fast

start-up. The large storage fills slowly but once it is filled up it provides a large buffer for

times where no energy is available, e.g. at night in a solar powered sensor.

STM 300 provides a digital output CCO (see also 3.7) which allows controlling the charging

of these two storages. At the beginning, as long as the voltage is below the VON voltage

only the small storage is filled. Once the threshold is reached the CCO signal changes and

the large storage is filled. The short term storage capacitor (C1) is usually in the range of

470 to 1000 µF. For the long term storage we suggest a capacitor (C2) with a capacity of

0.25 F. Below an overview and the schematics of a charging circuitry is shown:

This circuit is designed for an energy storage capacitor specified for 3.3 V (e.g. PAS614L-

VL3. Please pay great attention to manufacturers handling and soldering procedures!)