The output capacitor is selected based on holdup and transient (VTRAN) load requirements.
Time it takes LOUT to change 90% of its full load current:
During load transients most of the current will immediately go through the capacitors equivalent series resistance (ESRCOUT). The following equations are used to select ESRCOUT and COUT based on a 90% load step in current. The ESR is selected for 90% of the allowable transient voltage (VTRAN), while the output capacitance (COUT) is selected for 10% of VTRAN.
Before selecting the output capacitor, the output capacitor RMS current (ICOUT_RMS) must be calculated.
To meet the design requirements five 1500-µF, aluminum electrolytic capacitors are chosen for the design from United Chemi-Con™, part number EKY-160ELL152MJ30S. These capacitors have an ESR of 31 mΩ.
Number of output capacitors:
Total output capacitance:
Effective output capacitance ESR:
Calculate output capacitor loss (PCOUT):
Recalculate remaining Power Budget: