JAJSR90A September 2023 – July 2024 LMQ64480-Q1 , LMQ644A0-Q1 , LMQ644A2-Q1
PRODUCTION DATA
The output capacitor value and ESR determine the output voltage ripple and load transient performance. The output capacitor is usually limited by the load transient requirements rather than the output voltage ripple. Table 8-2 can be used to find capacitor values for COUT and CFF for a few common applications. Note that 4.99-kΩ RFF can be used in series with CFF to limit high frequency noise into the FB pin. In this example, 3.3 VOUT and 2.1 MHz, good transient performance is desired. From the table select 3 × 22-µF ceramic as the output capacitor and 10 pF as CFF. For other voltage a frequency combinations Cout can be estimated using the desired crossover frequency (fx) and output voltage. Crossover is usually limited by the sampling pole created from the switching frequency. Thus, the crossover is usually a percentage such as 1/10th the switching frequency.
FREQUENCY | IOUT | TRANSIENT PERFORMANCE | 3.3-V OUTPUT | 5-V OUTPUT | ||
---|---|---|---|---|---|---|
COUT (per phase) | CFF | COUT | CFF | |||
400 kHz | 6 A | Minimum | 3 × 47-µF ceramic | 2 × 47-µF ceramic | ||
400 kHz | 6 A | Better Transient | 4 × 47-µF ceramic | 10 pF | 3 × 47-µF ceramic | 10 pF |
2.1 MHz | 6 A | Minimum | 3 × 22-µF ceramic | 2 × 22-µF ceramic | ||
2.1 MHz | 6 A | Better Transient | 4 × 22-µF ceramic | 10 pF | 3 × 22-µF ceramic | 10 pF |