I am interested in two types of energy harvesting applications: Solar and piezoelectric energy harvesting.
From what I know it is essential is such low power applications to use some form of mppt, in order to maximize the power output of the harvester.
I have found the LTC 3108 for solar and the LTC 3588 for piezo. In both cases I could not find a reference in the datasheet of mppt implementation.
My question is, are these chips the right choice for such applications? I can see that they embed a lot of different functions for charging and advanced signaling and interfacing, but how can I ensure that my harvesting sources are used in the most efficient way, without some form of mppt?
Some form of input regulation is always necessary, but that's not always "MPPT" exactly. These examples do it a little differently and less obviously than some of our more recent designs.…
Some form of input regulation is always necessary, but that's not always "MPPT" exactly. These examples do it a little differently and less obviously than some of our more recent designs.
LTC3108 is not so straightforward. You need to choose your external circuitry to get the most out of the input source, but there's only so much you can do. There are some example applications in the datasheet that discuss this.
LTC3588 uses a UVLO regulation method where your input is kept bouncing between the rising/falling UVLO thresholds. These thresholds depend on the output voltage and can be seen in the spec table. You can use resistors to drop voltage at the input such that you extract voltage at the Vmpp of your input source (see apps circuits). Of course, this is not ideal unless your input source happens to naturally have its Vmpp within the UVLO window already since the resistors drop power.
Our later parts (see LTC3330, for example) allow you to customize this UVLO window to tailor to your device's Vmpp, which is a much better solution.