MIC2182 datasheet(14/40 Pages) MICROCHIP

14 / 40 page

MIC2182

DS20006644A-page 14



2022 Microchip Technology Inc. and its subsidiaries

A block diagram of the MIC2182 PWM current-mode

control loop is shown in Figure 4-1 and the PWM mode

voltage and current waveforms are shown in

Figure 4-3. The inductor current is sensed by

measuring the voltage across the resistor, RCS. A ramp

is added to the amplified current-sense signal to

provide slope compensation, which is required to

prevent unstable operation at duty cycles greater than

50%.

A transconductance amplifier is used for the error

amplifier, which compares an attenuated sample of the

output voltage with a reference voltage. The output of

the error amplifier is the COMP (compensation) pin,

which is compared to the current-sense waveform in

the PWM block. When the current signal becomes

greater than the error signal, the comparator turns off

the high-side drive. The COMP pin (Pin 3) provides

access to the output of the error amplifier and allows

the use of external components to stabilize the voltage

loop.

4.1.3

SKIP-MODE CONTROL LOOP

This control method is used to improve efficiency at

light output loads. At light output currents, the power

drawn by the MIC2182 is equal to the input voltage

times the IC supply current (IQ). At light output currents,

the power dissipated by the IC can be a significant

portion of the total output power, which lowers the

efficiency of the buck converter. The MIC2182 draws

less supply current in skip mode by disabling portions

of the control and drive circuitry when the IC is not

switching. The disadvantage of this method is greater

output voltage ripple and variable switching frequency.

A block diagram of the MIC2182 skip mode is shown in

Figure 4-2. Skip mode voltage and current waveforms

are shown in Figure 4-4.

FIGURE 4-2:

Skip-Mode Operation.

Low

Comp

Skip-Mode

Current

Limit

0.07V

LOW

FORCES

PWM MODE

–2%VBG

VIN

VDD

Reference

MIC2182 [adj.] Skip Mode

VOUT

CSH

VDD

VBST

CIN

VIN

HSD

CBST

COUT

VIN

VOUT

VSW

LSD

PGND

4.7F

1.245V

OUT =+

Current

Sense

Amp

CONTROL LOGIC AND

SKIP-MODE LOGIC

RCS

AV = 2

ONE SHOT

LOW-SIDE DRIVER

ONE SHOT

Hysteresis

Comp

(

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