JAJSHS0C March 2019 – March 2021 TPS92682-Q1
PRODUCTION DATA
The input capacitor, CIN, reduces the input voltage ripple and stores energy to supply input current during input voltage or PWM dimming transients. The series inductor in the Boost and SEPIC topologies provides continuous input current and requires a smaller input capacitor to achieve desired input voltage ripple, ΔvIN(PP). The Buck-Boost and Flyback topologies have discontinuous input current and require a larger capacitor to achieve the same input voltage ripple. Based on the switching frequency, fSW, and the maximum duty cycle, DMAX, the input capacitor value can be calculated for each channel as follows:
Boost:
Buck-Boost:
X7R dielectric-based ceramic capacitors are the best choice due to their low ESR, high ripple current rating, and good temperature performance. For applications using PWM dimming, TI recommends large bulk capacitors in addition and in parallel to the ceramic capacitors to minimize the voltage deviation due to large input current transients generated in conjunction with the rising and falling edges of the LED current.
Decouple the VIN pin with a 0.1-µF ceramic capacitor, placed as close as possible to the device, and optionally in series with a 10-Ω resistor to create a 160-kHz low-pass filter.