AMC3202DMF
Lower values are chosen to reduce physical size of the inductor, and higher values reduce
ripple voltage and core loss. In continuous conduction mode, the peak inductor current is
equal to average current plus half of the ripple current, which should not cause inductor
saturation. Based on the tolerance of the ripple current in the circuits, the following
formula (2) can be referenced:
In Boost circuits, the inductor becomes part of the input filter. In continuous mode,
the input current waveform is triangular and does not contain a large pulsed current. This
reduces the requirements imposed on the input capacitor selection. Capacitors in the range
of 10uF to 100uF with an ESR less than 0.3¦ work well up to full 1.5A switch current.
The VIN ripple is determined by the product of the inductor current ripple and the ESR
of input capacitor, and the VOUT ripple comes from two major sources, namely ESR of
output capacitor and the charging/discharging of the output capacitor. Ceramic capacitors
have the lowest ESR, but too low ESR may cause loop stability problems. Aluminum
Electrolytic capacitors exhibit the highest ESR, resulting in the poorest AC response. One
option is to parallel a ceramic capacitor with an Aluminum Electrolytic capacitor.
The goal of frequency compensation is to achieve desirable transient response and DC
regulation while ensuring the stability of the system. A typical compensation network, as
shown in the typical application circuit, provides a frequency response of two poles and
one zero. The loop frequency compensation is performed on the output of the error
amplifier (COMP pin) with a series RC network. The main pole is formed by the series
capacitor and the output impedance of the error amplifier. The series resistor creates a
zero, which improves loop stability and transient response.A second capacitor,is
sometimes used to reduce the switching frequency ripple on the COMP pin.
6/6
TGS [ Tiger Electronic Co.,Ltd ]
