MIC4575 Micrel Semiconductor, MIC4575 Datasheet - Page 5

• Manufacturer Part Number: MIC4575
• Description: 200kHz Simple 1A Buck Voltage Regulator
• Manufacturer: Micrel Semiconductor

MIC4575
Functional Description
The MIC4575 is a variable duty cycle switch-mode regulator
with an internal power switch. Refer to the block diagrams.
Supply Voltage
The MIC4575 operates from a +4V to +24V unregulated
input. Highest efficiency operation is from a supply voltage
around +15V.
Enable/Shutdown
The shutdown (
input if unused. A logic-low enables the regulator. A logic-
high shuts down the internal regulator which reduces the
current to typically 50 A.
Feedback
Fixed versions of the regulator have an internal resistive
divider from the feedback (
output line.
Adjustable versions require an external resistive voltage
divider from the output voltage to ground, connected from the
1.23V tap to
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 200kHz sawtooth
waveform to produce a voltage controlled variable duty cycle
output.
Applications Information
The applications circuits that follow have been constructed
and tested. Refer to Application Note 15 for additional
information, including efficiency graphs and manufacturer’s
addresses and telephone numbers for most circuits.
Note 2: Surface-
mount component.
Figure 1. 6V–24V to 3.3V/1A Buck Converter
6V to 24V
150µF
35V
C1
FB
C1 Nichicon
C2 Nichicon
D1 Motorola
L1 Sumida
L1 Bi
.
SHDN
5
1
SHDN
V
MIC4575-3.3BT
IN
) input is TTL compatible. Ground the
Through Hole
GND
3
HM77-11003, DCR = 0.233 , Note 2
UPL1V151MPH, ESR = 0.12
UPL1C331MPH, ESR = 0.12
1N5819
RCH106-680K, DCR = 0.22
FB
) pin. Connect
Figure 3. 16V–24V to 12V/1A Buck Converter, Through Hole
SW
FB
2
4
16V to 24V
D1
1N5819
68µF
68µH
63V
C1
L1
FB
C1 Nichicon
C2 Nichicon
D1 Motorola
L1 Sumida
5
1
3.3V/1A
directly to the
C2
330µF
16V
SHDN
V
IN
MIC4575BT
GND
3
UPL1J680MPH, ESR = 0.17
UPL1C331MPH, ESR = 0.12
MBR160
RCH110-151K, DCR = 0.23
SW
4-110
FB
2
4
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 com-
parator output. A lower feedback voltage increases the duty
cycle.
Output Switching
When the internal switch is on, an increasing current flows
from the supply V
output capacitor C
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 C
Output Capacitor
External output capacitor C
reduces ripple.
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.
For a mathematical approach to component selection and
circuit design, refer to Application Note 14.
MBR160
150µH
L1
Figure 2. 8V–24V to 5V/1A Buck Converter
8V to 24V
150µF
35V
C1
R2
13.0k
1%
R1
1.50k
1%
C1 Nichicon
C2 Nichicon
D1 Motorola
L1 Sumida
L2 Bi
5
1
IN,
12V/1A
SHDN
V
OUT
MIC4575-5.0BT
IN
C2
330µF
16V
through external storage inductor L1, to
Through Hole
and the load. Energy is stored in the
GND
3
UPL1J151MPH, ESR = 0.12
UPL1C331MPH, ESR = 0.12
1N5819
RCH106-680K, DCR = 0.22
HM77-11003, DCR = 0.233 , Note 2
OUT
SW
FB
OUT
2
4
provides stabilization and
.
D1
1N5819
68µH
L1
5.0V/1A
C2
330µF
16V
April 1998•
Micrel