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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 200A 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. 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 * < 200A 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 100H
5.0V/0.5A
8V to 24V C1 47F 35V
5
MIC4574-5.0BN FB VIN SGND PGND
2 4
1
D1 1N5819
C2 220F 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
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M9999-062105
MIC4574
Micrel, Inc.
Ordering Information
Standard Part Number Pb-Free MIC4574-3.3YN MIC4574-5.0YN MIC4574YN Voltage 3.3V 5.0V Adjustable Temperature Range -40C to +85C -40C to +85C -40C to +85C Package 8-pin DIP 8-pin DIP 8-pin DIP
MIC4574-3.3BN MIC4574-5.0BN MIC4574BN
Pin Configuration
FB 1 SGND 2 SHDN 3 PGND 4 8 7 6 5 NC SW NC VIN
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
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MIC4574
Micrel, Inc.
Absolute Maximum Ratings (Note 1)
Supply Voltage (VIN), Note 5 ...................................... +40V Shutdown (VSHDN) ....................................... -0.3V to +36V Output Switch (VSW) steady state ................................. -1V Junction Temperature (TJ) ...................................... +150C Storage Temperature ............................... -65C to +150C ESD Rating, Note 3
Operating Ratings (Note 2)
Supply Voltage (VIN) ................................................... +24V Package Thermal Resistance JA Plastic DIP .................................................. 130C/W
Electrical Characteristics (Note 4)
VIN =12V; ILOAD = 100mA; TA = 25C, bold values indicate -40C TA +85C; 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 IOUT = 0.5A FB connected to 0V Peak Current, tON 3s VIN = 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 A V V 1.0 0.8 30 10 V V A A 8V VIN 24V, 0.1A ILOAD 0.5A 4.900 4.800 4.750 5.0 5.0 77 5.100 5.200 5.250 V V V % 6V VIN 24V, 0.1A ILOAD 0.5A 3.234 3.168 3.135 3.3 3.3 72 3.366 3.432 3.465 V V V % 8V VIN 24V, 0.1A ILOAD 0.5A ILOAD = 0.5A, VOUT = 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) VOUT = 0V (regulator off) VOUT = 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.
VIN
Shutdown Enable
CIN
SHDN
Internal Regulator 200kHz Oscillator Thermal Shutdown Current Limit
Comparator
Driver 0.5A Switch 1.23V Bandgap R1 R2 GND
SW D1
L1 VOUT COUT
Error Amp. MIC4574-x.x
FB
Block Diagram with External Components Fixed Step-Down Regulator
+24V max.
VIN
Shutdown Enable
CIN
SHDN
Internal Regulator 200kHz Oscillator Thermal Shutdown Current Limit VOUT V REF
R1 +1 R2 1
R1 Comparator Driver 0.5A Switch 1.23V Bandgap
R2
VOUT VREF
SW D1
L1 VOUT COUT
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 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 50A. 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. For a mathematical approach to component selection and circuit design, refer to "Application Note 14."
L1
3
SHDN
SW
7
3.3V/0.5A
8V to 24V
3
SHDN
SW
7
L1 100H
5.0V/0.5A
100H
1
6V to 24V C1 47F 35V
5
MIC4574-3.3BN VIN FB SGND PGND
2 4
D1 1N5819
C2 220F 16V
5
C1 47F 35V
MIC4574-5.0BN FB VIN SGND PGND
2 4
1
D1 1N5819
C2 220F 16V
C1 C2 D1 L1
Nichicon Nichicon Motorola Sumida
UPL1V470MEH, ESR = 0.34 UPL1C221MPH, ESR = 0.16 1N5819 RCH875-101K, DCR = 0.28
C1 C2 D1 L1
Nichicon Nichicon Motorola Sumida
UPL1J470MEH, ESR = 0.34 UPL1C221MPH, ESR = 0.16 1N5819 RCH875-101K, DCR = 0.28
Figure 1. 6V-24V to 3.3V/0.5A Buck Converter Through Hole
Figure 2. 8V-24V to 5V/0.5A Buck Converter Through Hole
3
SHDN
SW
7
L1 220H R2 13.0k 1% R1 1.50k 1%
12V/0.5A
16V to 24V C1 33F 63V
5
MIC4574BN FB VIN SGND PGND
2 4
1
MBR160
C2 220F 16V
C1 C2 D1 L1
Nichicon Nichicon Motorola Sumida
UPL1J330MEH, ESR = 0.35 UPL1C221MPH, ESR = 0.16 MBR160 RCH106-221K, DCR = 0.78
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)
0.135 (3.43) 0.125 (3.18)
0.255 (6.48) 0.245 (6.22) 0.300 (7.62)
0.013 (0.330) 0.010 (0.254) 0.018 (0.57) 0.100 (2.54) 0.130 (3.30) 0.0375 (0.952) 0.380 (9.65) 0.320 (8.13)
8-Pin DIP (N)
MICREL INC.
TEL
2180 FORTUNE DRIVE
FAX
SAN JOSE, CA 95131 USA
WEB
+ 1 (408) 944-0800
+ 1 (408) 474-1000
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. (c) 2003 Micrel, Incorporated.
June 2005
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M9999-062105

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