In practice, the total output capacitance is typically comprised of a combination of different capacitors, in which larger capacitors provide the load current at lower frequencies and smaller capacitors provide the load current at higher frequencies. The value, type, and location of the output capacitors are critical for correct operation. TI recommends low-ESR multilayer ceramic capacitors with an X7R dielectric (or similar) for best performance.

The TPS6287x devices feature a butterfly layout with two GND pins on opposite sides of the package. This allows the output capacitors to be placed symmetrically on the PCB such that the electromagnetic fields generated cancel each other out, thereby reducing EMI.

The transient response of the converter is limited by one of two criteria:

• The slew rate of the current through the inductor, in which case, the feedback loop of the converter saturates.
• The maximum allowed ratio of converter bandwidth to switching frequency, in which the converter remains in regulation (that is, the loop does not saturate). TI recommends a minimum ratio of four for typical applications.

Which of the above criteria applies in any given application depends on the operating conditions and component values used. Therefore, TI recommends that the user calculate the output capacitance for both cases, and select the higher of the two values.

If the converter remains in regulation, the minimum output required capacitance is given by:

If the converter loop saturates, the minimum output capacitance is given by:

In this case, choose C_OUT(min) = 203µF as the larger of the two values for the output capacitance.

When calculating worst-case component values, use the value calculated above as the minimum output capacitance required. For ceramic capacitors, the maximum capacitance when considering tolerance, DC bias, temperature, and aging effects is typically two times the minimum capacitance. In this case, the maximum capacitance C_OUT(max) is 406μF.