All-Ceramic Capacitors Enable the Smallest Footprint for a 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 0.68µH, resulting in a footprint of 8.2mm × 8.2mm for 6A output current, further reducing buck converter size.

In Figure 1, the output inductor is the largest external component with the footprint of 8.2mm × 8.2mm. However, with the new developments at TOKO and Sumida we expect the inductor size to be reduced to 7.2mm × 7.2mm, further reducing the regulator footprint size.

Figure 2 shows the output ripple voltage, whose peak-to-peak value is less than 10mV for 1.8V output, well less than 1%.

Figure 3 shows the load transient response. With two 47µF ceramic output capacitors, the maximum output voltage deviation can meet ±5% for 50% step load change (3A). In addition, the transient response finishes within 10µs. Table 1 lists the bill of materials.