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I have a BQ25504EVM-674 Energy Harvesting Power Management with Battery Charging (EHM) development board by Texas Instruments. It fulfills my requirement of charging an energy store (e.g. supercap/rechargeable battery) and producing output voltage that can appropriately power a MCU (MSP430). The BQ25504 also has a boost converter, meant to be used with solar panels.

Most importantly for my design - It outputs a VBAT_OK (battery level) indicator that toggles high when the stored energy ramps up to 2.8V DC and toggles low when the energy store discharges and ramps down to 2.4V DC. Lets call these voltage thresholds V1 and V2 respectively.

As mentioned above, in the BQ25504EVM-674 by TI the V1 and V2 are fixed in the factory (V1=2.8V, V2=2.4V) by surface mount resistors on the board. If one needs to change these thresholds, then one has to de-solder the resistors and solder back appropriate resistors to get the required voltage levels. TI provides a spreadsheet to calculate the resistors, voltages etc.

However, I was wondering -

  1. is there another EHM which has similar functionality to the BQ25504EVM but with adjustable VBAT_OK voltage thresholds ?
  2. Or does anyone know how to change the resistor settings on the BQ25504EVM easily without desoldering ?
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    \$\begingroup\$ Why don't you want to desolder the resistors as your data sheet suggests? You could graft in appropriately sized potentiometers in place of the resistors and you have yourself a way to adjust the threshold. To avoid de-soldering (for whatever reason) you could solder in additional resistors in series or in parallel with the existing resistors by cutting tracks for the series ones, and soldering parallel resistors on top of existing ones etc. \$\endgroup\$ – IC_Eng May 2 at 8:36
  • \$\begingroup\$ @IC_Eng - I don't have de-soldering equipment nor have I done it before. Also, my hands are not as steady as they used to be. More importantly, I want to test the design easily against a 'range' of voltage thresholds, which means in the current board, i'll have to keep changing resistors. Hence, I'm looking for a similar board to the BQ255xx but with potentiometers or preset selectable thresholds. Does not matter which company the board is from. \$\endgroup\$ – bd3lk May 2 at 8:46
  • \$\begingroup\$ This Digikey page MAY help digikey.com/products/en/development-boards-kits-programmers/… \$\endgroup\$ – Russell McMahon May 2 at 13:52
  • \$\begingroup\$ Soldering a single wire to the centre of each resistor pair should allow external connection of resistors or a pot to modify onboard voltages. \$\endgroup\$ – Russell McMahon May 3 at 8:25

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