MIC33263 datasheet(15/19 Pages) MICREL

15 / 19 page

Micrel, Inc.

MIC33263/4

Over 100mA, efficiency loss is dominated by MOSFET

RDSON and inductor losses. Higher input supply voltages

will increase the gate-to-source threshold on the internal

MOSFETs, thereby reducing the internal RDSON. 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

on.

The

asynchronous switching combination between the PMOS

and the NMOS allows the control loop to work in

discontinuous

mode

for

light

load

operations.

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.

Figure 3. SW Frequency vs. Output

Emission Characteristic of MIC33263/4

The MIC33263/4 integrates switching components in a

single

package,

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.

100

1000

10000

100

1000

10000

OUTPUT CURRENT (mA)

Switching Frequency

vs. Output Current

VIN = 3.6V

VIN = 5V

OUT = 2V

May 15, 2014

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