10.2.1.2.3 Accounting for Resistor Tolerance

The previous sections described the selection of R_ILIM given certain application requirements and the importance of understanding the current-limit threshold tolerance. The analysis focused only on TPS25221 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. The following table shows a process that accounts for worst-case resistor tolerance assuming 1% resistor values. Step one follows the selection process outlined in the application examples above. 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.