After valid VIN is plugged in and CE pin is pulled LOW, the device checks the resistor on the ISET pin for shortcircuit (R_ISET < R_{ISET_SHORT}). If the condition is detected, charger remains in the FAULT state until the input or CE pin are toggled. If the ISET pin is open-circuit, the charger will charge with very low charging current in the order of 1.5 mA. 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 pull-down resistor (±1% or better recommended to minimize charge current error) from ISET pin to GND sets the charge current as:

• I_CHG is the desired fast charge current
• K_ISET is a gain factor found in the electrical specification (typically 300 AΩ )
• R_ISET is the pull-down resistor from ISET pin to GND

For charge currents below 50 mA, an extra RC circuit using a 50 pF capacitance is recommended on ISET to achieve more stable current signal. The ISET pin can also be used to monitor device current when the device is not in ICHG regulation. The voltage on the ISET pin is proportional to the device charging current. To measure the charge current when the device is charging, the following formula can be used:

• V_ISET is the measured voltage at the ISET pin in volts.
• I_CHG is the calculated measured charge current