As with all buck converters, the input current of the TPS6287x-Q1 devices is discontinuous. The input capacitors provide a low-impedance energy source for the device, and their value, type, and location are critical for correct operation. TI recommends low-ESR multilayer ceramic capacitors for best performance. In practice, the total input capacitance typically comprises a combination of different capacitors, in which larger capacitors provide the decoupling at lower frequencies and smaller capacitors provide the decoupling at higher frequencies.

The TPS6287x-Q1 devices feature a butterfly layout with two VIN pin pairs on opposite sides of the package. This allows the input capacitors to be placed symmetrically on the PCB such that the electromagnetic fields generated cancel each other out, thereby reducing EMI.

The duty cycle of the converter is given by:

where:

• V_IN is the input voltage
• V_OUT is the output voltage
• η is the efficiency

The value of input capacitance needed to meet the input voltage ripple requirements is given by:

where:

• D is the duty cycle
• f_sw is the switching frequency

• V_IN(PP) is the input voltage ripple

• I_OUT is the output current

The value of C_IN calculated with Equation 10 is the effective capacitance after all derating, tolerance, and ageing effects have been considered. We recommend multilayer ceramic capacitors with an X7R dielectric (or similar) for C_IN, and these capacitors must be placed as close to the VIN and GND pins as possible, so as to minimize the loop area.