MIC33030 datasheet(14/24 Pages) MICROCHIP

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MIC33030

DS20006026B-page 14



2018 - 2022 Microchip Technology Inc.

RDS(ON). This improves efficiency by reducing DC

losses in the device. All but the inductor losses are

inherent to the device. In which case, inductor selection

becomes increasingly critical in efficiency calculations.

As the inductors are reduced in size, the DC resistance

(DCR) can become quite significant.

The DCR losses can be calculated by using

Equation 5-2:

EQUATION 5-2:

From that, the loss in efficiency due to inductor

resistance can be calculated by using Equation 5-3:

EQUATION 5-3:

Efficiency loss due to DCR is minimal at light loads and

gains significance as the load is increased. Inductor

selection becomes a trade-off between efficiency and

size in this case.

The effect of MOSFET voltage drops and DCR losses

in conjunction with the maximum duty cycle combine to

limit maximum output voltage for a given input voltage.

Figure 5-2 shows this relationship based on the typical

resistive losses in the MIC33030:

FIGURE 5-2:

VOUT(MAX) vs. VIN

5.6

HyperLight Load® Mode

MIC33030 uses a minimum on-time 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.

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 MIC33030 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

MIC33030 during light load currents by only switching

when it is needed. As the load current increases, the

MIC33030 goes into continuous conduction mode

(CCM) and switches at a frequency centered at 8 MHz.

The equation to calculate the load when the MIC33030

goes into continuous conduction mode may be

approximated by the following Equation 5-4:

EQUATION 5-4:

The load at which MIC33030 transitions from

HyperLight Load® mode to PWM mode is a function of

the input voltage (VIN), output voltage (VOUT), duty

cycle (D), inductance (L), and frequency (f). Because

the inductance of MIC33030 is 0.36 µH, the device will

enter HyperLight Load® mode or PWM mode at

approximately 150 mA.

5.7

Power Dissipation Considerations

As with all power devices, the ultimate current rating of

the output is limited by the thermal properties of the

package and the PCB it is mounted on. There is a

simple, ohms law type relationship between thermal

resistance, power dissipation, and temperature which

are analogous to an electrical circuit:

PDCR IOUT

2 DCR



EfficiencyLoss

VOUT IOUT



VOUT IOUT PDCR



----------------------------------------------------









–

100



ILOAD

VIN VOUT

–







2L f



--------------------------------------------



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