C2 measures the battery-charging current by generating a proportional voltage at the OUT terminal (pin 2). The resulting drop across R2 produces a voltage at pins 3 and 4. When the charging current drops below 0.01C, for instance, this voltage crosses the internal comparator threshold and drives COUT1 low and setting COUT2 to high impedance. By disconnecting COUT2, the feedback level is shifted, which changes the charging voltage to approximately 13.4V. The maximum available charging current depends on VIN, the transformer's saturation current, and the current-sense resistor R1.