After a valid VIN is plugged in and CE pin is pulled LOW, 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 CE 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 recommended to minimize charge current error) from 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 ISET pin to GND

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