R1EN and R2EN serve as the voltage divider to program the supply input UVLO threshold using the following formula R1_EN =(V_ON/V_UVLOIN-1)*R2_EN, where VUVLOIN is the EN rising threshold (1.24V) and VON is the desired input startup voltage. EN pin has a small leakage current (50nA TYP, 700nA MAX), referring to the EN Leakage Current vs. Temperature curve from the datasheet below. (Rev 4 3/16)
This leakage current will introduce error in the UVLO threshold voltage. Representing this error mathematically,
eA = (IL * R1_EN)/V_ON, where eA is the ratio of voltage error introduced by leakage current to the desired input startup voltage (0.01 represents 1%), IL is the worst (maximum) leakage current of EN, R1_EN is the resistor connected to V_IN, and V_ON is the desired input startup voltage.
Combining the two formula above, for a given V_ON, increase of R2_EN will lead to increase of R1_EN, which in turn will increase eA. Therefore, as R2_EN increases, error increases. Smaller R2 can reduce the error but will increase the power consumption of the voltage divider network. Balancing the tradeoff between error and power consumption, a resistor in the range of 10Kohm~50kohm is recommended for R2_EN.