MICREL MIC4574

MIC4574
Micrel, Inc.
MIC4574
200kHz Simple 0.5A Buck Regulator
General Description
Features
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 current 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 compensation is provided internally.
• 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
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.
Typical Application
Shutdown
Enable
8V to 24V
C1
47µF
35V
3
5
SHDN
SW
MIC4574-5.0BN
FB
VIN
SGND PGND
2
7
L1
5.0V/0.5A
100µH
1
4
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
Standard
Part Number
Pb-Free
MIC4574-3.3BN
MIC4574-3.3YN
MIC4574-5.0BN
MIC4574-5.0YN
MIC4574BN
MIC4574YN
Voltage
Temperature
Range
Package
3.3V
–40°C to +85°C
8-pin DIP
5.0V
–40°C to +85°C
8-pin DIP
Adjustable
–40°C to +85°C
8-pin DIP
Pin Configuration
FB 1
8
NC
SGND 2
7
SW
SHDN 3
6
NC
PGND 4
5
VIN
8-Pin DIP (N)
Pin Description
Pin Number
Pin Name
1
FB
2
SGND
Signal Ground.
3
SHDN
Shutdown (Input): Logic low enables regulator. Logic high (> 2.4V) shuts
down regulator.
4
PGND
Power Ground.
5
VIN
Supply Voltage (Input): Unregulated +4V to +24V supply voltage.
7
SW
Switch (Output): Emitter of NPN output switch. Connect to external storage
inductor and Shottky diode.
6, 8
NC
Not internally connected. Solder to printed circuit for maximum heat transfer.
M9999-062105
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.
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June 2005
MIC4574
Micrel, Inc.
Absolute Maximum Ratings (Note 1)
Operating Ratings (Note 2)
Supply Voltage (VIN), Note 5 ...................................... +40V
Shutdown (VSHDN) ....................................... –0.3V to +36V
Output Switch (VSW) steady state ................................. –1V
Junction Temperature (TJ) ...................................... +150°C
Storage Temperature ............................... –65°C to +150°C
ESD Rating, Note 3
Supply Voltage (VIN) ................................................... +24V
Package Thermal Resistance
θJA Plastic DIP .................................................. 130°C/W
Electrical Characteristics (Note 4)
VIN =12V; ILOAD = 100mA; TA = 25°C, bold values indicate –40°C ≤ TA ≤ +85°C; unless noted
Parameter
Condition
Min
Typ
Max
Units
1.217
1.230
1.243
V
1.193
1.180
1.230
1.267
1.280
V
V
MIC4574 [Adjustable]
Feedback Voltage
Feedback Voltage
8V ≤ VIN ≤ 24V, 0.1A ≤ ILOAD ≤ 0.5A
Efficiency
ILOAD = 0.5A, VOUT = 5V
77
Feedback Bias Current
%
50
100
500
nA
nA
3.234
3.3
3.366
V
3.168
3.135
3.3
3.432
3.465
V
V
MIC4574-3.3
Output Voltage
Output Voltage
6V ≤ VIN ≤ 24V, 0.1A ≤ ILOAD ≤ 0.5A
Efficiency
72
%
MIC4574-5.0
Output Voltage
Output Voltage
8V ≤ VIN ≤ 24V, 0.1A ≤ ILOAD ≤ 0.5A
4.900
5.0
5.100
V
4.800
4.750
5.0
5.200
5.250
V
V
Efficiency
77
%
MIC4574 / -3.3 / -5.0
Oscillator Frequency
180
Saturation Voltage
IOUT = 0.5A
Maximum Duty Cycle (On)
FB connected to 0V
Current Limit
Peak Current, tON ≤ 3µs
Output Leakage Current
VIN = 24V, FB connected to 6V
Output = 0V
Output = –1V
SHDN = 5V (regulator off)
SHDN Input Logic Level
VOUT = 0V (regulator off)
Note 1.
Note 2.
Note 3.
Note 4.
Note 5.
1
1.3
1.5
V
V
0.7
0.65
1.0
1.6
1.8
A
A
0
7.5
2
35
mA
mA
5
10
mA
50
200
µA
2.2
2.4
SHDN = 5V (regulator off)
SHDN = 0V (regulator on)
kHz
95
VOUT = 3.3V or 5V (regulator on)
SHDN Input Current
220
90
Quiescent Current
Standby Quiescent Current
200
–10
%
1.4
V
V
1.2
1.0
0.8
V
V
4
0.01
30
10
µA
µA
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.
VIN
Shutdown
Enable
SHDN
CIN
Internal
Regulator
Thermal
Shutdown
200kHz
Oscillator
Current
Limit
Driver
Comparator
L1
SW
VOUT
0.5A
Switch
D1
COUT
1.23V
Bandgap
Error
Amp.
R1
FB
R2
MIC4574-x.x
GND
Block Diagram with External Components
Fixed Step-Down Regulator
+24V max.
VIN
Shutdown
Enable
SHDN
CIN
Internal
Regulator
Thermal
Shutdown
200kHz
Oscillator
VOUT
Current
Limit
R1
Comparator
Driver
V REF
R2
R1
+ 1
R2
VOUT
VREF
1
L1
SW
VOUT
0.5A
Switch
D1
COUT
Error
Amp.
1.23V
Bandgap
R1
FB
MIC4574 [Adjustable]
R2
GND
Block Diagram with External Components
Adjustable Step-Down Regulator
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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 comparator output. A lower feedback voltage increases the duty
cycle.
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.
Output Capacitor
External output capacitor COUT 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
MIC4574
Micrel, Inc.
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.
L1
3
6V to 24V
5
C1
47µF
35V
SHDN
MIC4574-3.3BN
VIN
FB
SGND PGND
2
C1
C2
D1
L1
SW
Nichicon
Nichicon
Motorola
Sumida
4
For a mathematical approach to component selection and
circuit design, refer to “Application Note 14.”
3.3V/0.5A
7
3
100µH
8V to 24V
C2
220µF
16V
1
D1
1N5819
C1
47µF
35V
16V to 24V
C1
33µF
63V
5
C1
C2
D1
L1
7
SW
Nichicon
Nichicon
Motorola
Sumida
L1
220µH
MIC4574BN
FB
VIN
SGND PGND
2
Nichicon
Nichicon
Motorola
Sumida
4
7
L1
5.0V/0.5A
100µH
1
D1
1N5819
C2
220µF
16V
UPL1J470MEH, ESR = 0.34Ω
UPL1C221MPH, ESR = 0.16Ω
1N5819
RCH875-101K, DCR = 0.28Ω
Figure 2. 8V–24V to 5V/0.5A Buck Converter
Through Hole
Figure 1. 6V–24V to 3.3V/0.5A Buck Converter
Through Hole
SHDN
SW
MIC4574-5.0BN
FB
VIN
SGND PGND
2
C1
C2
D1
L1
UPL1V470MEH, ESR = 0.34Ω
UPL1C221MPH, ESR = 0.16Ω
1N5819
RCH875-101K, DCR = 0.28Ω
3
5
SHDN
1
MBR160
4
12V/0.5A
R2
13.0k
1%
R1
1.50k
1%
C2
220µF
16V
UPL1J330MEH, ESR = 0.35Ω
UPL1C221MPH, ESR = 0.16Ω
MBR160
RCH106-221K, DCR = 0.78Ω
Figure 3. 16V–24V to 12V/0.5A Buck Converter
Through Hole
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June 2005
MIC4574
Micrel, Inc.
Package Information
PIN 1
DIMENSIONS:
INCH (MM)
0.380 (9.65)
0.370 (9.40)
0.255 (6.48)
0.245 (6.22)
0.135 (3.43)
0.125 (3.18)
0.300 (7.62)
0.013 (0.330)
0.010 (0.254)
0.018 (0.57)
0.130 (3.30)
0.100 (2.54)
0.380 (9.65)
0.320 (8.13)
0.0375 (0.952)
8-Pin DIP (N)
MICREL INC.
TEL
2180 FORTUNE DRIVE
+ 1 (408) 944-0800
FAX
SAN JOSE, CA 95131 USA
+ 1 (408) 474-1000
WEB
http://www.micrel.com
This information furnished by Micrel in this data sheet is believed to be accurate and reliable. However no responsibility is assumed by Micrel for its use.
Micrel reserves the right to change circuitry and specifications at any time without notification to the customer.
Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can
reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into
the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchaser’s
use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser’s own risk and Purchaser agrees to fully indemnify
Micrel for any damages resulting from such use or sale.
© 2003 Micrel, Incorporated.
June 2005
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