FLF3215T-R47N datasheet(15/19 Pages) MICREL

15 / 19 page

Micrel, Inc.

MIC23163/4

July 29, 2013

Revision 2.0

HyperLight Load Mode

MIC23163/4 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 MIC23163/4 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 MIC23163/4 during

light load currents by only switching when it is needed. As

the load current increases, the MIC23163/4 goes into

continuous conduction mode (CCM) and switches at a

frequency centered at 4MHz. The equation to calculate

the load when the MIC23163/4 goes into continuous

conduction mode may be approximated by Equation 6:

(

)













−

OUT

LOAD

Eq. 6

As shown in Equation 6, the load at which the

MIC23163/4 transitions from HLL mode to PWM mode is

a function of the input voltage (VIN), output voltage (VOUT),

duty cycle (D), inductance (L) and frequency (f). As

shown in Figure 4, as the output current increases, the

switching frequency also increases until the MIC23163/4

goes from HLL mode to PWM mode at approximately

120mA. The MIC23163/4 will switch at a relatively

constant frequency around 4MHz once the output current

is over 120mA.

Figure 4. SW Frequency vs. Output Current

100

1000

10000

100

1000

10000

OUPUT CURRENT (mA)

Switching Frequency vs.

Output Current

IN = 5V

IN = 3.6V

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