ZHCSGZ6A October 2017 – February 2025 TPS6508700
PRODUCTION DATA
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TI recommends using ceramic capacitors with low ESR values to provide the lowest output voltage ripple. The output capacitor requires an X7R or an X5R dielectric. Y5V and Z5U dielectric capacitors, aside from their wide variation in capacitance over temperature, become resistive at high frequencies.
At light load currents, the controller operates in PFM mode, and the output voltage ripple is dependent on the output-capacitor value and the PFM peak inductor current. Higher output-capacitor values minimize the voltage ripple in PFM mode. To achieve the specified regulation performance and low output-voltage ripple, the DC-bias characteristic of ceramic capacitors must be considered. The effective capacitance of ceramic capacitors drops with increasing DC bias voltage.
TI recommends using small ceramic capacitors placed between the inductor and load with many vias to the power ground (PGND) plane for the output capacitors of the buck controllers. This solution typically provides the smallest and lowest cost solution available for D-CAP2 controllers.
The selection of the output capacitor is typically driven by the output transient response. Equation 6 provides a rough estimate of the minimum required capacitance to ensure proper transient response. Because the transient response is significantly affected by the board layout, some experimentation is expected to confirm that values derived in this section are applicable to any particular use case. Equation 6 is not meant to be an absolute requirement, but rather a rough starting point. Alternatively, some known combination values from which to begin are provided in Table 7-1.

where
In cases where the transient current change is very low, the DC stability may become important. Use Equation 7 to calculate the approximate amount of capacitance required to maintain DC stability. Again, this equation is provided as a starting point; actual values will vary on a board-to-board case.

where
The maximum valuable between Equation 6 and Equation 7 must be selected. Table 7-1 lists some known inductor-capacitor combinations.
| ITRAN(max) (A) | L (μH) | VOUT (V) | VUNDER (V) | COUT(μF) |
|---|---|---|---|---|
| 3.5 | 0.47 | 1 | 0.05 | 110 |
| 4 | 0.47 | 1 | 0.05 | 220 |
| 5 | 0.47 | 1.35 | 0.068 | 220 |
| 8 | 0.33 | 1 | 0.06 | 440 |
| 20 | 0.22 | 1 | 0.16 | 550 |