PowerXR products have a couple of sequencing requirements for proper power up. The VCCA 5V regulator is used to power the drivers and analog circuitry, including the 1.8V regulator which powers the digital section of the part. The 1.8V regulator must come up into regulation before the Enable pin is logic high. This is needed to allow the Enable pin to act as the internal reset of the digital logic. So the Enable pin must be delayed. The second reason for delaying the Enable pin is to ensure that the input voltage has risen above the VIN UVLO (under voltage lock out) fault level. If this is not done, erroneous faults can occur.