MIC33050_09 Datasheet, PDF (10/13 Pages) Micrel Semiconductor – 4MHz Internal Inductor PWM Buck Regulator with HyperLight Load

Micrel, Inc.
MIC33050
HyperLight Load™ Mode
The MIC33050 uses a minimum on and off time
proprietary control loop. When the output voltage falls
below the regulation threshold, the error comparator
begins a switching cycle that turns the PMOS on and
keeps it on for the duration of the minimum-on-time. When
the output voltage is over the regulation threshold, the
error comparator turns the PMOS off for a minimum-off-
time. The NMOS acts as an ideal rectifier that conducts
when the PMOS is off. Using a NMOS switch instead of a
diode allows for lower voltage drop across the switching
device when it is on. The asynchronous switching
combination between the PMOS and the NMOS allows the
control loop to work in discontinuous mode for light load
operations. In discontinuous mode, MIC33050 works in
pulse frequency modulation (PFM) to regulate the output.
As the output current increases, the switching frequency
increases. This improves the efficiency of the MIC33050
during light load currents. As the load current increases,
the MIC33050 goes into continuous conduction mode
(CCM) at a constant frequency of 4MHz. The equation to
calculate the load when the MIC33050 goes into
continuous conduction mode may be approximated by the
following formula:
I_LOAD
=
⎜⎛
⎝
(V_IN
− V_OUT )
2L × f
×
D
⎟⎞
⎠
July 2009
10
M9999-070909-C