MIC4680 datasheet(11/24 Pages) MICROCHIP

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2021 Microchip Technology Inc. and its subsidiaries

DS20006623A-page 11

MIC4680

4.0

FUNCTIONAL DESCRIPTION

The MIC4680 is a variable duty cycle switch-mode

regulator with an internal power switch. Refer to the

Functional Block Diagrams.

4.1

Supply Voltage

The MIC4680 operates from a +4V to +34V

unregulated input. Highest efficiency operation is from

a supply voltage around +15V. See Figure 2-10

through Figure 2-12.

4.2

Enable/Shutdown

The shutdown (SHDN) input is TTL compatible.

Ground the input if unused. A logic low enables the

regulator. A logic high shuts down the internal regulator

which reduces the current to typically 1.5 μA when

VSHDN = VIN = 12V and 30 μA when VSHDN = 5V. See

Figure 1-2.

4.3

Feedback

Fixed-voltage versions of the regulator have an internal

resistive divider from the feedback (FB) pin. Connect

FB directly to the output voltage.

Adjustable versions require an external resistive

voltage divider from the output voltage to ground,

center tapped to the FB pin. See Table 5-1 for

recommended resistor values.

4.4

Duty Cycle Control

A fixed-gain error amplifier compares the feedback

signal with a 1.23V bandgap voltage reference. The

resulting error amplifier output voltage is compared to a

200 kHz

sawtooth

waveform

produce

voltage-controlled variable duty cycle output.

A higher feedback voltage increases the error amplifier

output voltage. A higher error amplifier voltage

(comparator inverting input) causes the comparator to

detect only the peaks of the sawtooth, reducing the

duty cycle of the comparator output. A lower feedback

voltage increases the duty cycle. The MIC4680 uses a

voltage mode control architecture.

4.5

Output Switching

When the internal switch is on, an increasing current

flows from the supply VIN, through external storage

inductor L1, to output capacitor COUT and the load.

Energy is stored in the inductor as the current

increases with time.

When the internal switch is turned off, the collapse of

the magnetic field in L1 forces current to flow through

fast recovery diode D1, charging COUT.

4.6

Output Capacitor

External output capacitor COUT provides stabilization

and reduces ripple. See the Bode Plots for additional

information.

4.7

Return Paths

During the ON portion of the cycle, the output capacitor

and load currents return to the supply ground. During

the OFF portion of the cycle, current is being supplied

to the output capacitor and load by storage inductor L1,

which means that D1 is part of the high-current return

path.

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