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TI BQ25570 Step-Up DC-DC Energy Harvester and battery charger

During the development of the Scrobby prototypes I've developed a strong interest in low power electronics. I noticed the recent news on the TI BQ25570 and did a quick implementation of one of the reference designs.

What is this BQ25570?

In short: The Texas Instruments BQ25570 is an integrated IC with functions ususally found separately. The most newsworthy bit is a relatively simple (in terms of external parts) MPPT capable boost converter able to boost from as little as 100mV! Also onboard is an integrated battery charger, suitable for multiple types of batteries (like LiPo). Finally a step-down converter provides a regulated output voltage.

Design

The board is an implementation of figure 3 of the datasheet and takes a TEG or similar input voltage and tries (using MPPT) to load this to 50% of the open loop voltage. The output is set to 2.5V and the battery is configured for a single LiPo cell.

Schematic
Schematic

larger view

BOM

  • C1, C7 22uF 3216
  • C2, C5, C6 0.1µF 1608
  • C3 10nF 1608
  • C4 4.7µF 2012
  • L1 22µH Abracon ASPI-0418FS
  • L2 10µH 2520 TDK MLP2520S100ST0S1
  • P1, P2, P3 2.54mm 2 pin header
  • R1 7.87MΩ 1608
  • R2 6.04MΩ 1608
  • R3 0.698MΩ 1608
  • R4 8.06MΩ 1608
  • R5 4.22MΩ 1608
  • R6 6.65MΩ 1608
  • R7 6.19MΩ 1608
  • U1 QFN-20-TE TI BQ25570

Board

You can grab the board straight from OSHPark , download the gerber files: BQ25570_Harvester or the KiCad project files: BQ25570_Harvester .

PCB top side PCB bottom side