SNVSBW1C December 2021 – August 2024 LM63440-Q1 , LM63460-Q1
PRODUCTION DATA
The value of the output capacitor and the ESR determine the output voltage ripple and load transient performance. The output capacitor is usually determined by load transient and stability requirements rather than the output voltage ripple. For LM63440-Q1, use Table 8-7 and for LM63460-Q1, use Table 8-8 to select the output capacitance and CFF feedforward capacitance values for a few common applications. Use a 1kΩ RFF in series with CFF to further improve noise performance.
CONFIGURATION | 3.3V OUTPUT | 5V OUTPUT | ||
---|---|---|---|---|
COUT | CFF | COUT | CFF | |
2.1MHz – Ceramic | 3 × 22µF, 16V ceramic | 10pF | 2 × 47µF, 10V ceramic | 10pF |
2.1MHz – Alternative | 2 × 22µF, 16V ceramic + 47µF, 10mΩ electrolytic |
– | 2 × 47µF, 10V ceramic + 47µF, 10mΩ electrolytic |
– |
400kHz – Ceramic | 4 × 22µF, 16V ceramic | 33pF | 2 × 47µF, 10V ceramic | 22pF |
400kHz – Alternative | 1 × 22µF, 16V ceramic + 100µF, 10mΩ electrolytic |
15pF | 1 × 47µF, 10V ceramic + 47µF, 10mΩ electrolytic |
10pF |
CONFIGURATION | 3.3V OUTPUT | 5V OUTPUT | ||
---|---|---|---|---|
COUT | CFF | COUT | CFF | |
2.1MHz – Ceramic | 4 × 22µF, 16V ceramic | 10pF | 2 × 47µF, 10V ceramic | 10pF |
2.1MHz – Alternative | 2 × 22µF, 16V ceramic + 100µF, 10mΩ electrolytic |
– | 2 × 47µF, 10V ceramic + 100µF, 10mΩ electrolytic |
– |
400kHz – Ceramic | 5 × 22µF, 16V ceramic | 15pF | 3 × 47µF, 10V ceramic | 15pF |
400kHz – Alternative | 2 × 22µF, 16V ceramic + 100µF, 10mΩ electrolytic |
– | 1 × 47µF, 10V ceramic + 100µF, 10mΩ electrolytic |
– |
Most ceramic capacitors deliver less capacitance than the rating of the capacitor indicates. Be sure to check selected capacitors for initial accuracy, temperature derating, and particularly voltage derating. Table 8-7 and Table 8-8 assumes typical derating for X7R-dielectric capacitors. If lower voltage or lower temperature-rated capacitors are used, more capacitance than listed can be required.
More conveniently, Equation 11 calculates the required effective ceramic capacitance for a given application:
where FC is the target loop crossover frequency in units of kHz, which can be set at 10% to 15% of switching frequency and up to a maximum of 100kHz.
This example requires improved transient performance, resulting in two 47µF, 10V, X7R ceramics as the output capacitance and 10pF for CFF. An alternative configuration is to use a low-ESR electrolytic capacitor in parallel with a reduced ceramic capacitance.