The peak current limit of the converter indicates the maximum peak inductor current which limits the output current (similar if implementing valley current limit). In the IBB configuration, the inductor current and peak switching currents are larger than in the equivalent buck converter. Consequently, the output current capability in the IBB topology is less than the buck configuration for the same current limit specifications. The maximum achievable current is calculated by Equation 1.

where

• I_{L_MAX} is the maximum rated inductor current
• D is the operating duty cycle

Calculate the operating duty cycle for an inverting buck-boost converter using Equation 2.

where

• η = Efficiency

The efficiency term in Equation 2 adjusts the equations in this section for power conversion losses and yields a more accurate maximum output current result. Given that the IBB configuration yields different efficiency values compared to a buck, use a conservative value or see Table 2-1 or Figure 5-1 for typical efficiency values. Use Equation 2 to find the expected duty cycle, then use Equation 1 to calculate the recommended maximum output current. For example, in a 24-V input voltage, –5-V output voltage system, the duty cycle is:

The result of Equation 3 is then used to calculate the maximum recommended output current:

Table 2-1 and Figure 2-1 provide a general idea of the recommended maximum output current allowed from the TPSM5601R5H in an inverting configuration, with given typical efficiency values.