MIC23451 datasheet(16/28 Pages) MICROCHIP

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MIC23451

DS20006662A-page 16



2022 Microchip Technology Inc. and its subsidiaries

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 MIC23451 works in

pulse-frequency modulation (PFM) to regulate the

output. As the output current increases, the off-time

decreases, which provides more energy to the output.

This switching scheme improves the efficiency of

MIC23451 during light load currents by switching only

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

MIC23451 goes into continuous conduction mode

(CCM) and switches at a frequency centered at 3 MHz.

The equation to calculate the load when the MIC23451

goes into continuous conduction mode is approximated

in Equation 5-10.

EQUATION 5-10:

As shown in that equation, the load at which the

MIC23451 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). Figure 5-3 shows that as the output

current increases, the switching frequency also

increases until the MIC23451 goes from HyperLight

Load mode to PWM mode at approximately 120 mA.

The MIC23451 will switch at a relatively constant

frequency around 3 MHz after the output current is over

120 mA.

FIGURE 5-3:

Switching Frequency vs.

Output Current.

5.9

Multiple Sources

The MIC23451 provides all the pins necessary to

operate the three regulators from independent

sources. This can be useful in partitioning power within

a multi-rail system. For example, two supplies may be

available within a system: 3.3V and 5V. The MIC23451

can be connected to use the 3.3V supply to provide

two, low-voltage outputs (for example, 1.2V and 1.8V)

and use the 5V rail to provide a higher output (for

example, 2.5V), resulting in the power blocks shown in

Figure 5-4.

FIGURE 5-4:

Multi-Source Power Block

Diagram.

ILOAD

VIN VOUT

–







2L f



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



0.1

100

1000

10000

0.0001

0.001

0.01

0.1

OUTPUT CURRENT (A)

VOUT = 1.8V

VIN = 5V

VIN = 3V

VIN = 3.6V

3.3V

1.8V

1.2V

2.5V

CH1

CH2

CH3

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