MCP73871 - IC Getting Hot or Charger Stops

Why does the MCP73871 charger start, then the IC gets hot and the charger stops, and then restarts?

This is due to a temperature fault and the charger stops due to an increase in temperature. When the temperature decreases in some time, the charger restarts. This could be because of a lack of proper power dissipation.

There is a directional control MOSFET present between IN pin and OUT pin. See the "Functional Block Diagram" in the datasheet under "Documents" on the MCP73871 product page.

  1. Measure the voltage drop across this MOSFET.
  2. The voltage drop value is multiplied by the current supplied to the charger to get the power value.
  3. Power value is then used to calculate the junction temperature using the formula: Tj = (theta-JC x Power dissipated ) + Tcase. This can give an estimate of what the junction temperature is and can be compared to FIG 2-14 ("Charge Current (IOUT) vs. Junction Temperature (TJ)"). We can see that charge current quickly drops off when Tj reaches around 125°C. This increase in temperature causes the IC to stop and restart again after it cools down. To overcome this problem, we must look at dissipating power appropriately or reduce the current.
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