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MIC4575
200kHz Simple 1A Buck Regulator
General Description
The MIC4575 is a series of easy to use fixed and adjustable BiCMOS step-down (buck) switch-mode voltage regulators. The 200kHz MIC4575 duplicates the pinout and function of the 52kHz LM2575. The higher switching frequency may allow up to a 2:1 reduction in output filter inductor size. The MIC4575 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 1A 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 MIC4575 is available in TO-220 (T) and TO-263 (U) packages for 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 1A 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% typical) Standard inductors and capacitors are25% of typical LM2575 values * Thermal shutdown * Overcurrent protection * 100% electrical thermal limit burn-in
Applications
* * * * * * * Simple high-efficiency step-down (buck) regulator Efficient pre-regulator for linear regulators On-card switching regulators Positive-to-negative converter (inverting buck-boost) Battery charger Negative boost converter Step-down 6V to 3.3V for Intel Pentium(R) and similar microprocessors
___________________________________________________________________________________________________________
Typical Application
Shutdown Enable 5
SHDN
SW
2
L1 68H
5.0V/1A C2 330F 16V
8V to 24V C1 150F 35V
1
MIC4575-5.0_T VIN FB GND
3
4
D1 1N5819
Fixed Regulator
Pentium is a registered trademark of Intel Corporation
Adjustable 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
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Micrel, Inc.
MIC4575
Ordering Information
Part Number Standard MIC4575-3.3BT MIC4575-5.0BT MIC4575BT MIC4575-3.3BU MIC4575-5.0BU MIC4575BU RoHS Compliant* MIC4575-3.3WT MIC4575-5.0WT MIC4575WT MIC4575-3.3WU MIC4575-5.0WU MIC4575WU Voltage 3.3V 5.0V Adj. 3.3V 5.0V Adj. Temperature Range -40 to +85C -40 to +85C -40 to +85C -40 to +85C -40 to +85C -40 to +85C Package 5-Pin TO-220 5-Pin TO-220 5-Pin TO-220 5-Pin TO-263 5-Pin TO-263 5-Pin TO-263
* RoHS compliant with `high-melting solder' exemption.
Pin Configuration
5 4 3 2 1 SHDN FB GND SW VIN
5-Pin TO-220 (T)
TAB
5-Pin TO-263 (U)
Pin Description
Pin Number 1 2 3, TAB 4 Pin Name IN SW GND FB Pin Function Supply Voltage (Input): Unregulated +4V to +40V supply voltage. Switch (Output): Emitter of NPN output switch. Connect to external storage inductor and Shottky diode. Ground. 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. Shutdown (Input): Logic low enables regulator. Logic high (> 2.4V) shuts down regulator.
5
SHDN
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Absolute Maximum Ratings
Supply Voltage (VIN) ..................................................+40V Shutdown Voltage (VSHDN)............................. -0.3V to +36V Output Switch (VSW) .......................................................-1V Storage Temperature (Ts) ........................... -65C to 150C ESD(2)
(1)
Operating Ratings
Supply Voltage (VIN).....................................................+24V Junction Temperature (TJ) ....................................... +150C Package Thermal Resistance TO-220, TO-263 (JA) ........................................65C/W TO-220, TO-263 (JC) ..........................................2C/W
Electrical Characteristics(4)
VIN = 12V; ILOAD = 200mA; TJ = 25C, bold values indicate -40C< TJ < +85C, unless noted.
Parameter MIC4575 [Adjustable] Feedback Voltage Feedback Voltage Efficiency Feedback Bias Current MIC4575-3.3 Output Voltage Output Voltage Efficiency MIC4575-5.0 Output Voltage Output Voltage Efficiency MIC4575 / -3.3 / -5.0 Oscillator Frequency Saturation Voltage Maximum Duty Cycle (On) Current Limit Output Leakage Current 3.234 6V VIN 24V, 0.2A ILOAD 1A ILOAD = 1A 4.900 8V VIN 24V, 0.2A ILOAD 1A ILOAD = 1A 180 IOUT = 1A FB connected to 0V Peak Current, tON 3s VIN = 24V, FB connected to 0V Output = 0V Output = -1V SHDN = 5V (regulator off) VOUT = 0V (regulator off) VOUT = 3.3 or 5V (regulator on) SHDN = 5V (regulator off) SHDN = 0V (regulator on)
Notes: 1. The MIC4575 is not guaranteed to survive a short circuit to ground for input voltage above 24V. 2. Devices are ESD sensitive. Handling precautions recommended.
Condition
Min 1.217
Typ 1.230 1.230 77 50
Max 1.243 1.267 1.280 100 500 3.366 3.432 3.465
Units V V V % nA nA V V V % V V V % kHz V V % A A mA mA mA A V V V V A A
8V VIN 24V, 0.2A ILOAD 1A ILOAD = 1A, VOUT = 5V
1.193 1.180
3.168 3.135
3.3 3.3 72 5.0 5.0 77 200 1 95 2.2
5.100 5.200 5.250
4.800 4.750
220 1.3 1.5 3.0 3.2 2 35 10 200
90 1.7 1.3
Quiescent Current Standby Quiescent Current SHDN Input Logic Level SHDN Input Current
2.2 2.4
0 7.5 5 50 1.4 1.2 4 0.01
-10
1.0 0.8 30 10
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Functional Diagram
Block Diagram with External Components Fixed Step-Down Regulator
Block Diagram with External Components Adjustable Step-Down Regulator
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MIC4575 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 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 (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 the1.23V 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.
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Application 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.
Figure 4. 6V-24V to 3.3V/1A Buck Converter Low-Profile Surface Mount
Figure 1. 6V-24V to 3.3V/1A Buck Converter Through Hole Figure 5. 8V-24V to 5V/1A Buck Converter Low-Profile Surface Mount
Figure 2. 8V-24V to 5V/1A Buck Converter Through Hole
L1 150H
4
Figure 6. 16V-24V to 12V/1A Buck Converter Low-Profile Surface Mount
5
SHDN VIN GND
3
SW FB
2
12V/1A R2 13.0k 1% R1 1.50k 1%
16V to 24V C1 68F 63V
1
MIC4575BT
MBR160
C2 330F 16V
C1 C2 D1 L1
Nichicon Nichicon Motorola Sumida
MBR160
Figure 3. 16V-24V to 12V/1A Buck Converter Through Hole
Note 2: Surface-mount component.
Figure 7. 6V-24V to 3.3V/1A Buck Converter Lower-Cost Surface Mount
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MIC4575
Figure 8. 8V-24V to 5V/1A Buck Converter Lower-Cost Surface Mount
Figure 10. 8V-18V to -5V/0.2A Buck-Boost Converter Through Hole
Figure 9. 16V-24V to 12V/1A Buck Converter Lower-Cost Surface Mount Figure 11. 5V to -5V/0.3A Buck-Boost Converter Through Hole
5
SHDN MIC4575BU VIN
SW FB GND
3
2
4
T1 68H
3
L1 1H R2 3.01k 1% R1 1.00K 1% C3 3300pF
VOUT 5V/1A 5mVP-P C2 220F 10V
VIN 8V to 18V C1 22F 35V C1 C2 C4 D1 T1 L1
1
4
1
2
D1 MBRS130LT3
C4 220F 10V
AVX AVX AVX Motorola MBRS130LT3 Coiltronics Coilcraft DO1608C-102
Figure 12. Low Output-Noise Regulator (5mV Output Ripple )
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MIC4575
5
VIN 8V to 18V C1 22F 35V
SHDN MIC4575BU VIN
SW FB
2
2
T1 68H
1
+VOUT/+IOUT 5V/0.5A R2 3.01k 1% R1 1.00K 1% C3 3300pF
1
4
GND
3
D1 MBRS130LT3
4
C2 220F 10V
C5 220F 10V
3
L1
D2 MBRS130LT3
C4 220F 10V -VOUT/-IOUT -5V/0.5A at VIN 15V Load Regulation 5%
+I
C1 C2 C4 C5 D1 D2 T1 AVX AVX AVX AVX Motorola MBRS130LT3 Motorola MBRS130LT3 Coiltronics
+ -I
A
+V + 0.5V DC V - 0.5V 40% then - I 40% then - I
x (1 - DC)
Figure 13. Split 5V Supply
Figure 14. Adjustable (0V-12V) Output-Voltage Regulator
U1
5
SHDN
SW
2
L1 68H
3
VOUT 1V/1A
VIN 4V to 15V
1
MIC4575BT FB VIN GND
3
4
1 2
U2 LM358
C1 150F 35V
D1 1N5819
C2 330F 16V
R1 249 1%
R2 1.00k 1%
R3 1k
C1 C2 D1 Motorola 1N5819 L1 U2 National LM358
Figure 15. Low Output-Voltage Regulator (1V)
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Figure 16. 1A Battery Charger (6-8 cells)
D3 1N4148
5
L1 68H
VIN 8V to 24V
SHDN
SW
2
R1 0.1 R2 100 1% C2 330F 16V
D2 1N5819
IOUT 0.1A to 1A 2-8 Cells VBATT
1
MIC4575-BT FB VIN GND
3
4
R6 3k C4 1000pF
D1 1N5819
VIN R5 10k VR1 10k
C1 150F 35V U1 U2 U3 C1 C2 D1 D2 D3 L1 R1 Q1 Micrel National Micrel Nichicon Nichicon Motorola Motorola Motorola Coiltronics KRL Siliconix
3
R7 1k MIC4575BT LM358 LM4041CIZ-1.2 1N5819 1N5819 1N4148 SP-1-A1-0R100J VN2222LL
1 2
U2A 1/2LM358
R3 10k
VIN
8
U2B 1/2 LM358
5
C3 0.01F DZ1 1N5244 14V R4 1.21k 1%
7
U3 LM4041CIZ-1.2
Q1 VN2222LL
6 4
V
/ 0.9 + 2.5V
Figure 17. 0.1A-1A Variable-Current Battery Charger
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Figure 18. 1A Battery Charger (2-8 Cells)
Figure 19. Remote-Sensing Regulator
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MIC4575
Figure 20. 6V-18V to Split 12V/100mA Supply
Figure 21. 1A Battery Charger
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Figure 22. Improved Adjustable Output-Voltage Regulator (0V-12V)
Figure 23. Switchable Battery-Pack Charger
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MIC4575
Figure 25. Low Output-Noise Regulator (<1mV)
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Figure 24. Lithium-Ion Battery Charger with End-of-Charge Flag

M9999-072909
Micrel, Inc.
MIC4575
Package Information
5-Pin TO-220 (T)
5-Pin TO-263 (U)
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MIC4575
MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA
TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http://www.micrel.com
The 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) 1997 Micrel, Incorporated.
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