After a valid VIN is plugged in, the device checks the resistor on the ISET pin for a short circuit (R_ISET < R_{ISET_SHORT}). If a short condition is detected, the charger remains in the FAULT state until the input or TS pin is toggled. If the ISET pin is open-circuit, the charger proceeds through pin detection and starts the charger with no charge current. This pin is monitored while charging and changes in R_ISET while the charger is operating will immediately translate to changes in charge current.

An external pulldown resistor (±1% or better is recommended to minimize charge current error) from the ISET pin to GND sets the charge current as:

Equation 1.

where:

• I_CHG is the desired fast-charge current
• K_ISET is a gain factor found in the electrical specifications
• R_ISET is the pulldown resistor from the ISET pin to GND

For charge currents below 50 mA, an extra RC circuit is recommended on ISET to achieve a more stable current signal. For greater accuracy at lower currents, part of the current-sensing FET is disabled to give better resolution.