MIC4574
Micrel, Inc.
MIC4574
200kHz Simple 0.5A Buck Regulator
General Description
The MIC4574 is a series of easy to use fixed and adjustable
BiCMOS step-down (buck) switch-mode voltage regulators.
The 200kHz MIC4574 duplicates the pinout and function of
the 52kHz LM2574. The higher switching frequency may
allow up to a 2:1 reduction in output filter inductor size.
The MIC4574 is available in 3.3V, and 5V fixed output
versions or a 1.23V to 20V adjustable output version. Both
versions are capable of driving a 0.5A load with excellent line
and load regulation.
The feedback voltage is guaranteed to
±2%
tolerance for
adjustable versions, and the output voltage is guaranteed to
±3%
for fixed versions, within specified voltages and load
conditions. The oscillator frequency is guaranteed to
±10%.
In shutdown mode, the regulator draws less than 200µA
standby current. The regulator performs cycle-by-cycle cur-
rent limiting and thermal shutdown for protection under fault
conditions.
This series of simple switch-mode regulators requires a
minimum number of external components and can operate
using a standard series of inductors. Frequency compensa-
tion is provided internally.
The MIC4574 is available in the DIP (N) package and is rated
over the industrial temperature range.
Data sheets and support documentation can be found on
Micrel’s web site at www.micrel.com.
Features
• Fixed 200kHz operation
• 3.3V, 5V, and adjustable output versions
• Voltage over specified line and load conditions:
Fixed version:
±3%
max. output voltage
Adjustable version:
±2%
max. feedback voltage
• Guaranteed 0.5A switch current
• Wide 4V to 24V input voltage range
• Wide 1.23V to 20V output voltage range
• Requires minimum external components
• < 200µA typical shutdown mode
• 75% efficiency (adjustable version > 75% typ.)
• Standard inductors and capacitors are
25% of typical LM2574 values
• Thermal shutdown
• Overcurrent protection
• 100% electrical thermal limit burn-in
Applications
Simple high-efficiency step-down (buck) regulator
Efficient preregulator for linear regulators
On-card switching regulators
Positive-to-negative converter (inverting buck-boost)
Isolated flyback converter using minimum external
components
• Negative boost converter
•
•
•
•
•
Typical Application
Shutdown
Enable
3
SHDN
SW
7
L1
100µH
5.0V/0.5A
8V to 24V
C1
47µF
35V
5
MIC4574-5.0BN
FB
V
IN
SGND PGND
2
4
1
D1
1N5819
C2
220µF
16V
Fixed Regulator
Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
June 2005
1
M9999-062105
MIC4574
Micrel, Inc.
Ordering Information
Part Number
Standard
Pb-Free
MIC4574-3.3BN
MIC4574-5.0BN
MIC4574BN
MIC4574-3.3YN
MIC4574-5.0YN
MIC4574YN
Voltage
3.3V
5.0V
Adjustable
Temperature
Range
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
Package
8-pin DIP
8-pin DIP
8-pin DIP
Pin Configuration
FB 1
SGND 2
SHDN 3
PGND 4
8
7
6
5
NC
SW
NC
V
IN
8-Pin DIP (N)
Pin Description
Pin Number
1
Pin Name
FB
Pin Function
Feedback (Input): Output voltage feedback to regulator. Connect to output
of supply for fixed versions. Connect to 1.23V tap of resistive divider for
adjustable versions.
Signal Ground.
Shutdown (Input): Logic low enables regulator. Logic high (> 2.4V) shuts
down regulator.
Power Ground.
Supply Voltage (Input): Unregulated +4V to +24V supply voltage.
Switch (Output): Emitter of NPN output switch. Connect to external storage
inductor and Shottky diode.
Not internally connected. Solder to printed circuit for maximum heat transfer.
2
3
4
5
7
6, 8
SGND
SHDN
PGND
VIN
SW
NC
M9999-062105
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June 2005
MIC4574
Micrel, Inc.
Absolute Maximum Ratings
(Note 1)
Supply Voltage (V
IN
),
Note 5
...................................... +40V
Shutdown (V
SHDN
) ....................................... –0.3V to +36V
Output Switch (V
SW
) steady state ................................. –1V
Junction Temperature (T
J
) ...................................... +150°C
Storage Temperature ............................... –65°C to +150°C
ESD Rating,
Note 3
Operating Ratings
(Note 2)
Supply Voltage (V
IN
) ................................................... +24V
Package Thermal Resistance
θ
JA
Plastic DIP .................................................. 130°C/W
Electrical Characteristics
(Note 4)
V
IN
=12V; I
LOAD
= 100mA; T
A
= 25°C,
bold
values indicate –40°C
≤
T
A
≤
+85°C; unless noted
Parameter
MIC4574 [Adjustable]
Feedback Voltage
Feedback Voltage
Efficiency
Feedback Bias Current
MIC4574-3.3
Output Voltage
Output Voltage
Efficiency
MIC4574-5.0
Output Voltage
Output Voltage
Efficiency
MIC4574 / -3.3 / -5.0
Oscillator Frequency
Saturation Voltage
Maximum Duty Cycle (On)
Current Limit
Output Leakage Current
I
OUT
= 0.5A
FB connected to 0V
Peak Current, t
ON
≤
3µs
V
IN
= 24V, FB connected to 6V
Output = 0V
Output = –1V
90
0.7
0.65
180
200
1
95
1.0
1.6
1.8
2
35
10
200
220
1.3
1.5
kHz
V
V
%
A
A
mA
mA
mA
µA
V
V
1.0
0.8
30
10
V
V
µA
µA
8V
≤
V
IN
≤
24V, 0.1A
≤
I
LOAD
≤
0.5A
4.900
4.800
4.750
5.0
5.0
77
5.100
5.200
5.250
V
V
V
%
6V
≤
V
IN
≤
24V, 0.1A
≤
I
LOAD
≤
0.5A
3.234
3.168
3.135
3.3
3.3
72
3.366
3.432
3.465
V
V
V
%
8V
≤
V
IN
≤
24V, 0.1A
≤
I
LOAD
≤
0.5A
I
LOAD
= 0.5A, V
OUT
= 5V
1.217
1.193
1.180
1.230
1.230
77
50
100
500
1.243
1.267
1.280
V
V
V
%
nA
nA
Condition
Min
Typ
Max
Units
0
7.5
5
Quiescent Current
Standby Quiescent Current
SHDN Input Logic Level
SHDN = 5V (regulator off)
V
OUT
= 0V (regulator off)
V
OUT
= 3.3V or 5V (regulator on)
SHDN Input Current
Note 1.
Note 2.
Note 3.
Note 4.
Note 5.
50
2.2
2.4
1.4
1.2
4
0.01
SHDN = 5V (regulator off)
SHDN = 0V (regulator on)
–10
Exceeding the absolute maximum rating may damage the device.
The device is not guaranteed to function outside its operating rating.
Devices are ESD sensitive. Handling precautions recommended.
Specification for packaged product only.
The MIC4574 is not guaranteed to survive a short circuit to ground for input voltage above 24V.
June 2005
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M9999-062105
MIC4574
Micrel, Inc.
Block Diagrams
+24V max.
V
IN
Shutdown
Enable
C
IN
SHDN
Internal
Regulator
200kHz
Oscillator
Thermal
Shutdown
Current
Limit
Com-
parator
Driver
0.5A
Switch
1.23V
Bandgap
R1
R2
GND
SW
D1
L1
V
OUT
C
OUT
Error
Amp.
MIC4574-x.x
FB
Block Diagram with External Components
Fixed Step-Down Regulator
+24V max.
V
IN
Shutdown
Enable
C
IN
SHDN
Internal
Regulator
200kHz
Oscillator
Thermal
Shutdown
Current
Limit
V
OUT
V
REF
R1
+ 1
R2
1
R1
Com-
parator
Driver
0.5A
Switch
1.23V
Bandgap
R2
V
OUT
V
REF
SW
D1
L1
V
OUT
C
OUT
Error
Amp.
MIC4574
[Adjustable]
R1
FB
GND
R2
Block Diagram with External Components
Adjustable Step-Down Regulator
M9999-062105
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June 2005
MIC4574
Micrel, Inc.
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
IN,
through external storage inductor L1, to
output capacitor C
OUT
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 C
OUT
.
Output Capacitor
External output capacitor C
OUT
provides stabilization and
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.
Functional Description
The MIC4574 is a variable duty cycle switch-mode regulator
with an internal power switch. Refer to the block diagrams.
Supply Voltage
The MIC4574 operates from a +4V to +24V unregulated
input. Highest efficiency operation is from a supply voltage
below +15V.
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 50µA.
Feedback
Fixed versions of the regulator have an internal resistive
divider from the feedback (
FB
) pin. Connect
FB
directly to the
output line.
Adjustable versions require an external resistive voltage
divider from the output voltage to ground, connected from the
1.23V tap to
FB
.
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.
June 2005
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M9999-062105
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