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Cell protection: DW01 + 8205A

Batteries and solar · Advanced · about 20 minutes · part of Electronics Technician

Every Li-ion pack has a tiny board that disconnects the cell when it is in danger: over-charged, over-discharged, over-loaded or shorted. The DW01 watches the cell voltage and the voltage across two back-to-back MOSFETs (the 8205A) in the negative lead, and turns one of them off.

Cell protection: DW01 + 8205A: the circuit on the simulator's bench

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How it works

Each FET is about 25.1 mΩ at V_GS = 3.7 V, so at 370 mA the pair drops 2 × 25.1 mΩ × I = 19 mV.

The DW01 reads that drop on CS: above 150 mV (about 3 A) for 10 ms it opens the discharge FET; above 1.35 V (a short) instantly. Below 2.4 V it opens it to save the cell; above 4.3 V it opens the charge FET.

Try it on the bench

  1. Turn the load switch off after an over-current trip: the DW01 resets itself.
  2. Lower the cell (bench supply) slowly from 3.7 V: it cuts the load at 2.4 V and reconnects above 3.0 V.

Parts on the bench

In the course

Electronics Technician, module “Batteries, chargers and USB”.

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