9.1.2 Accounting for Resistor Tolerance

The tolerance of the resistor selected for R_ILIM will impact the current-limit threshold tolerance, which is important in many applications. The analysis in the following examples focuses only on the TPS2553-Q1 device performance and assumed an exact resistor value. However, resistors sold in quantity are not exact and are bounded by an upper and lower tolerance centered around a nominal resistance. The additional R_ILIM resistance tolerance directly affects the current-limit threshold accuracy at a system level. Table 1 shows a process that accounts for worst-case resistor tolerance assuming 1% resistor values. Step one follows the selection process outlined in the following application examples. Step two determines the upper and lower resistance bounds of the selected resistor. Step three uses the upper and lower resistor bounds in the I_OS equations to calculate the threshold limits. It is important to use tighter tolerance resistors, for example, 0.5% or 0.1%, when precision current-limiting is desired.