MIC33263 Datasheet, PDF (15/19 Pages) Micrel Semiconductor – Buck Regulator with Integrated Inductor

Micrel, Inc.
Over 100mA, efficiency loss is dominated by MOSFET
R_DSON and inductor losses. Higher input supply voltages
will increase the gate-to-source threshold on the internal
MOSFETs, thereby reducing the internal R_DSON. This
improves efficiency by reducing DC losses in the device.
HyperLight Load Mode (HLL)
MIC33263/4 uses a minimum on and off time proprietary
control loop (PCL) patented by Micrel called HyperLight
Load (HLL). 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. This increases
the output voltage. If the output voltage is over the
regulation threshold, then the error comparator turns the
PMOS off for a minimum-off-time until the output drops
below the threshold. 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, the MIC33263/4 works in pulse
frequency modulation (PFM) to regulate the output. As
the output current increases, the off-time decreases, thus
provides more energy to the output. This switching
scheme improves the efficiency of MIC33263/4 during
light load currents by only switching when it is needed. As
the load current increases, the MIC33263/4 goes into
continuous conduction mode (CCM) and switches at a
frequency centered at 4MHz.
As shown in Figure 3, as the output current increases,
the switching frequency also increases until the
MIC33263/4 goes from HLL mode to PWM mode at
approximately 120mA. The MIC33263/4 will switch at a
relatively constant frequency around 4MHz once the
output current is over 220mA.
MIC33263/4
Emission Characteristic of MIC33263/4
The MIC33263/4 integrates switching components in a
single package, so the MIC33263/4 has reduced
emission compared to standard buck regulator with
external MOSFETs and inductors. The radiated EMI
scans for MIC33263/4 are shown in the Functional
Characteristics. The limit on the graph is per EN55022
class B standard.
10000
Switching Frequency
vs. Output Current
1000
VIN = 3.6V
VIN = 5V
100
10
1
1
V_OUT = 2V
10
100
1000
10000
OUTPUT CURRENT (mA)
Figure 3. SW Frequency vs. Output
May 15, 2014
15
Revision 1.1