MIC24046 datasheet(22/38 Pages) MICROCHIP

22 / 38 page

MIC24046

DS20006677A-page 22



2022 Microchip Technology Inc.

The slope compensation is also internally adapted to

the input-output voltage differential.

In practical implementations of valley-current-mode

control, slope compensation is also added to any duty

cycle larger than 50% as part of improving current loop

stability and noise immunity for all input and output volt-

age ranges. Consequently, the MIC24046 adds internal

slope compensation signal up to 60% duty cycle.

Above this, no slope compensation is added. For this

reason, the PWM modulator gain exhibits an abrupt

change when the duty cycle exceeds 60%, possibly

leading to some increase in jitter and noise susceptibil-

ity.

If operation around and above 60% duty cycle is con-

sidered, a more conservative design of the compensa-

tion loop might help in reducing jitter and noise

sensitivity.

Inductor current ratings are generally stated as permis-

sible DC current and saturation current. Permissible

DC current can be rated for a 20°C to 40°C tempera-

ture rise. Saturation current can be rated for a 10% to

30% loss in inductance. Ensure that the nominal cur-

rent of the application is well within the permissible DC

current ratings of the inductor, depending on the

allowed temperature rise. Note that the inductor per-

missible DC current rating typically does not include

inductor core losses. These are very important contrib-

utors of total inductor core loss and temperature

increase in high-frequency DC/DC converters because

core losses increase rapidly with the excitation fre-

quency.

When saturation current is specified, make sure that

there are enough design margins so the peak current

does not cause the inductor to enter deep saturation.

Pay attention to the inductor saturation characteristic in

current limit. The inductor should not heavily saturate,

even in current limit operation. If there is heavy satura-

tion, the current may instantaneously run away and

reach potentially destructive levels. Typically, fer-

rite-core inductors exhibit an abrupt saturation charac-

teristic, while powdered-iron or composite inductors

have a soft-saturation characteristic. Peak current can

be calculated with Equation 5-4.

EQUATION 5-4:

As shown in Equation 5-4, the peak inductor current is

inversely proportional to the switching frequency and

the inductance. The lower the switching frequency or

inductance, the higher the peak current. As input volt-

age increases, the peak current also increases.

5.6

Output Capacitor Selection

Two main requirements determine the size and charac-

teristics of the output capacitor:

• Steady-state ripple

• Maximum voltage deviation during load transient

For steady-state ripple calculation, the ESR and the

capacitive ripple both contribute to the total ripple

amplitude.

From the switching frequency, input voltage, output

voltage setting, and load current, the peak-to-peak

inductor current ripple and the peak inductor current

can be calculated as:

EQUATION 5-5:

EQUATION 5-6:

The capacitive ripple ΔVR, C and the ESR ripple

ΔVR, ESR are given by:

TABLE 5-4:

RECOMMENDED

INDUCTANCE VALUES AT

VIN = 12V

VOUT Selection

Frequency

Minimum

Inductance

0.7V, 0.8V, 0.9V,

1.0V, 1.2V

400 kHz

0.97

565 kHz

0.68

790 kHz

0.49

1.5V, 1.8V

400 kHz

1.51

565 kHz

1.06

790 kHz

0.76

2.49V, 3.3V

400 kHz

2.42

565 kHz

1.70

790 kHz

1.21

IL PEAK



IO VO

1 VO VIN



–

2 f L



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











IL_PP VO

1 VO VIN



–

fS L



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









IL PEAK





IL_PP

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

MIC24046 Datasheet(PDF) 22 Page - Microchip Technology

MIC24046 Datasheet(HTML) 22 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38

Datasheet Download

Link URL