The unique design requirement for using the LSF family is calculating the values of the external pull-up resistors. Each channel should be calculated independently and there are two important criteria to remember. For high-speed operation, lower resistance will result in sharper rising edges and too low of external resistors may result in exceeding the current driving capability of the external drivers. First, look at the pull-up resistors when the A-side is driving a low level. Traditionally, the pull-up resistor value will be the same on both sides of the LSF device and the R_DS(on) of the pass transistor can be neglected. The pass transistor is on, so the current is being pulled through the pass transistor from the driver on the B-side.