MIC4721 Datasheet, PDF (14/19 Pages) Micrel Semiconductor – 1.5A 2MHz Integrated Switch Buck Regulator

Micrel, Inc.
MIC4721
5V_IN and 1.8V_OUT 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.
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 a feedforward capacitor is
graphed below.
3.3V_IN and 1.8V_OUT I_OUT = 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.
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.
May 2007
14
M9999-052907-A