POWER-SUPPLY CIRCUITS Nov 11, 2002
Small Footprint, 10us Response Time, 10mV
Output Ripple, 1MHz, 6A Step-Down Regulator
One benefit of high-frequency switching is the fast loop response. This translates to smaller
footprint and lower cost, because the ceramic capacitors can be used. The MAX1945 internal
switch step-down regulator is designed for high-frequency switching. It can be switched at
1MHz. Its peak current mode control architecture allows simple Type II compensation (R2 and
C2) to achieve high bandwidth, further reducing the external component count.
As shown in Figure 1, for 6A output, only two 1210 footprint ceramic capacitors are needed to
meet the 50% step load change, thus greatly reducing the output capacitor size when compared
to switching at 500kHz or less. A second benefit is due to the low ESR of the ceramic
capacitors. Large inductor ripple current is allowed to achieve the 1% ripple voltage
requirement.The value of the output inductor is 0.68uH, resulting in a footprint of 8.2mm x
8.2mm for 6A output current, further reducing buck converter size.