9.2.2.2.3 Output Capacitor Selection (C_OUT)

1. In the majority of applications, low ESR electrolytic or solid tantalum capacitors between 82 μF and 820 μF provide the best results. This capacitor must be placed close to the IC using short capacitor leads and short copper traces. Do not use capacitors larger than 820 μF.

NOTE

For additional information, see section on output capacitors in Output Capacitor (COUT) section.

2. To simplify the capacitor selection procedure, see Table 6 for a quick design guide. This table contains different output voltages, and lists various output capacitors that will provide the best design solutions.

From Table 6, locate the output voltage column. From that column, locate the output voltage closest to the output voltage in your application. In this example, select the 24-V line. Under the Output Capacitor (COUT) section, select a capacitor from the list of through-hole electrolytic or surface-mount tantalum types from four different capacitor manufacturers. TI recommends that both the manufacturers and the manufacturers' series that are listed in Table 6 be used.

In this example, through hole aluminum electrolytic capacitors from several different manufacturers are available.

• 220-μF, 35-V Panasonic HFQ Series
• 150-μF, 35-V Nichicon PL Series
3. The capacitor voltage rating must be at least 1.5 times greater than the output voltage, and often much higher voltage ratings are required to satisfy the low ESR requirements required for low output ripple voltage.

For a 20-V output, a capacitor rating of at least 30 V is required. In this example, either a 35-V or 50-V capacitor would work. A 35-V rating was chosen, although a 50-V rating could also be used if a lower output ripple voltage is required.

Other manufacturers or other types of capacitors may also be used, provided the capacitor specifications (especially the 100-kHz ESR) closely match the types listed in Table 6. Refer to the capacitor manufacturers data sheet for this information.