Designing the DS2726 to Protect Li+ Batteries During a Reverse Charger Event

Abstract: This application presents simple design modifications that will allow the DS2726 Li+ protector to withstand negative voltages and protect the battery during a reverse charger event.

A reverse charger connection can defeat the DS2726 Li+ protector circuit. Certain device pins are sensitive to negative voltages and will cause the IC to behave erratically. The DS2726's high-side p-channel FETs will turn off, but some pins height=394 alt="Figure 1. Modified typical application so the DS2726 passes a reverse charger connection." src="/data/attachment/portal/201007/ET12504201007191109491.gif" width=648>
Figure 1. Modified typical application so the DS2726 passes a reverse charger connection.

The DS2726 Li+ battery protector can be modified to protect the batteries if a charger is connected in reverse. There are some design tradeoffs to consider, but none of them are critical to the overall operation of the protector. The calculations in this application note assume the power rating of the resistors to be 250mW. Using higher power resistors will allow the use of smaller resistance values. Smaller resistance values will reduce both the offset error in the overcurrent threshold and the delay seen in CC turn-on/turn-off times. Caution must still be taken to ensure that the constant-current limit of the Schottky diodes is not exceeded.