MIC2145

Micrel, Inc.

M9999-042205

8

April 2005

Application Information

Pre-designed circuit information is at the end of this section.

Output Voltage

The output voltage of the regulator can be set between 2.4V

and 16V by connecting a resistor divider at the FB pin. The

resistor values are selected by the following equations:

R

VR

VV

OUT

2

108

1

108

=

−

.∑

.

Time 20µs

V

OUT

AC Couple

(100mV/div)

V

SW

(5V/div)

Figure 4. Without Feed-Forward Capacitor

Time 4µs

V

OUT

AC Couple

(100mV/div)

V

SW

(5V/div)

Figure 5. With Feed-Forward Capacitor (100pF)

A value of 1MΩ is recommended for R1 to minimize the

quiescent current when the part is off. Then, R2 can be solved

using the above equation. A feed-forward capacitor, C

ranging from 5pF to 100pF can be used in parallel with R1 to

reduce the peak-to-peak output voltage ripple, which is

shown in Figures 4 and 5.