MIC4721 datasheet(14/19 Pages) MICREL

14 / 19 page

Micrel, Inc.

MIC4721

May 2007

M9999-052907-A

5VIN and 1.8VOUT at 1.5A load;

•

Phase Margin = 43.1 Degrees

•

GBW = 218KHz

The non-synchronous MIC4721 regulator only has the

ability to source current. This means that the regulator

must rely on the load to sink current. This causes a non-

linear response at light loads. The following plot shows

the effects of the pole created by the nonlinearity of the

output drive during light load (discontinuous) conditions.

3.3VIN and 1.8VOUT IOUT = 50mA;

•

Phase Margin = 90.5 Degrees

•

GBW = 64.4KHz

Feed Forward Capacitor

The feedback resistors are a gain reduction block in the

overall system response of the regulator. By placing a

capacitor from the output to the feedback pin, high

frequency signal can bypass the resistor divider, causing

a gain increase up to unity gain.

The graph above shows the effects on the gain and

phase of the system caused by feedback resistors and a

feedforward capacitor. The maximum amount of phase

boost

achievable

with

feedforward

capacitor

graphed below.

By looking at the graph, phase margin can be affected to

a greater degree with higher output voltages. The next

bode plot shows the phase margin of a 1.8V output at

1.5A without a feedforward capacitor.

MIC4721 Datasheet(PDF) 14 Page - Micrel Semiconductor