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MIC4574
Micrel
MIC4574
200kHz Simple 0.5A Buck Voltage 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 DIP (N) and SOIC (WM) packages for the industrial temperature range.
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 Applications
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
L1 100H
3
Shutdown Enable
5
SHDN
SW
12
3.3V/0.5A R2 2.49k 1% R1 1.50k 1% C3 3300pF
6V to 24V C1 10F 35V
10
MIC4574BWM FB VIN SGND PGND
4 6
D1
C2 330F 6.3V
MBRS130LT3
Adjustable Regulator 4-92 April 1998*
MIC4574
Micrel
Ordering Information
Part Number MIC4574-3.3BN MIC4574-5.0BN MIC4574BN MIC4574-3.3BWM MIC4574-5.0BWM MIC4574BWM Voltage 3.3V 5.0V Adjustable 3.3V 5.0V Adjustable Temperature Range -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C Package 8-pin DIP 8-pin DIP 8-pin DIP 14-lead SOIC 14-lead SOIC 14-lead SOIC
Pin Configuration
NC 1 NC 2 FB 3
14 NC 13 NC 12 SW 11 NC 10 VIN 9 NC 8 NC
FB 1 SGND 2 SHDN 3 PGND 4
8 7 6 5
NC SW NC VIN
SGND 4 SHDN 5 PGND 6 NC 7
4
8-Pin DIP (N)
14-Lead Wide SOIC (WM)
Pin Description
Pin Number N Package Pin Number WM Package 1 2 1 3 Pin Name NC NC FB Pin Function Not internally connected. Solder to printed circuit for maximum heat transfer. Not internally connected. Solder to printed circuit for maximum heat transfer. 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 Not internally connected. Solder to printed circuit for maximum heat transfer. Not internally connected. Solder to printed circuit for maximum heat transfer. Not internally connected. Solder to printed circuit for maximum heat transfer. Supply Voltage (Input): Unregulated +4V to +24V supply voltage. Not internally connected. Solder to printed circuit for maximum heat transfer. 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. Not internally connected. Solder to printed circuit for maximum heat transfer.
2 3 4
4 5 6 7 8 9
SGND SHDN PGND NC NC NC VIN NC SW NC NC
5
10 11
7 8
12 13 14
April 1998*
4-93
MIC4574
Micrel
Absolute Maximum Ratings
Supply Voltage (VIN) Note 1 ....................................... +40V Shutdown (VSHDN) ....................................... -0.3V to +36V Output Switch (VSW) steady state ................................. -1V Junction Temperature (TJ) ...................................... +150C Storage Temperature ............................... -65C to +150C
Operating Ratings
Supply Voltage (VIN) ................................................... +24V Package Thermal Resistance JA Plastic DIP .................................................. 130C/W JC SOIC ........................................................... 120C/W
Electrical Characteristics
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 30 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 SHDN = 5V (regulator off) SHDN = 0V (regulator on) 2.2 2.4
50 1.4 1.2 4 0.01
-10
General Note: Devices are ESD protected, however, handling precautions are recommended. Note 1: The MIC4574 is not guaranteed to survive a short circuit to ground for input voltage above 24V.
4-94
April 1998*
MIC4574
Micrel
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
4
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
April 1998*
4-95
MIC4574
Micrel
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 logichigh 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. 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.
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
For a mathematical approach to component selection and circuit design, refer to Application Note 14.
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 FB VIN 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
3
Figure 2. 8V-24V to 5V/0.5A Buck Converter Through Hole
SW FB PGND
4 7
L1 220H R2 13.0k 1% R1 1.50k 1%
12V/0.5A
SHDN VIN SGND
2
16V to 24V C1 33F 63V
5
MIC4574BN
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 4-96 April 1998*
MIC4574
L1 100H
3
Micrel
3.3V/0.5A
5
5
SHDN
SW
12
L1 SHDN SW
12
3.3V/0.5A
6V to 24V C1 10F 35V
10
MIC4574BWM VIN FB SGND PGND
4 6
R2 2.49k 1% R1 1.50k 1%
C3 3300pF
100H
3
D1
C2 330F 6.3V
6V to 24V C1 68F 35V
10
MIC4574-3.3BWM FB VIN SGND PGND
4 6
D1 MBRS130LT3
C2 470F 16V
MBRS130LT3 C1 C2 D1 L1 AVX AVX Motorola Coiltronics TPSD106M035R0300, ESR = 0.3 TPSE337M006R0100, ESR = 0.1 MBRS130LT3 CTX100-2P, DCR = 0.541
C1 C2 D1 L1
Sanyo Sanyo Motorola Coilcraft
35CV168GX, ESR = 0.34 16CV470GX, ESR = 0.17 MBRS130LT3 DO3316P-104, DCR = 0.23
Figure 4. 6V-24V to 3.3V/0.5A Buck Converter Low-Profile Surface Mount
L1 100H
3
Figure 7. 6V-24V to 3.3V/0.5A Buck Converter Low-Cost Surface Mount
5
SHDN
SW
12
5V/0.5A R2 3.01k 1% R1 1.00k 1%
5
L1 SHDN SW
12
5V/0.5A
8V to 24V C1 10F 35V
10
MIC4574BWM FB VIN SGND PGND
4 6
C3 3300pF
100H
3
D1
C2 220F 10V
8V to 24V C1 68F 35V
10
MIC4574-5.0BWM FB VIN SGND PGND
4 6
D1 MBRS130LT3
C2 470F 16V
MBRS130LT3 C1 C2 D1 L1 AVX AVX Motorola Coiltronics TPSD106M035R0300, ESR = 0.3 TPSE227M010R0100, ESR = 0.1 MBRS130LT3 CTX100-2P, DCR = 0.541 C1 C2 D1 L1 Sanyo Sanyo Motorola Coilcraft 35CV168GX, ESR = 0.34 16CV470GX, ESR = 0.17 MBRS130LT3 DO3316P-104, DCR = 0.23
Figure 5. 8V-24V to 5V/0.5A Buck Converter Low-Profile Surface Mount
L1 250H
3
Figure 8. 8V-24V to 5V/0.5A Buck Converter Low-Cost Surface Mount
L1 220H
3
4
5
SHDN
SW
12
12V/0.5A R2 13.0k 1% R1 1.50k 1% C3 3300pF
5
SHDN
SW
12
12V/0.5A R2 13.0k 1% R1 1.50k 1%
16V to 24V C1 10F 50V
10
MIC4574BWM FB VIN SGND PGND
4 6
D1 SS16
C2 68F 20V
16V to 24V C1 47F 50V
10
MIC4574BWM FB VIN SGND PGND
4 6
D1 SS16
C2 470F 16V
C1 C2 D1 L1
Tokin C55Y5U1H106Z AVX TPSE686M020R0150, ESR = 0.15 General Instruments SS16 Coiltronics CTX250-4P, DCR = 0.434
C1 C2 D1 L1
Nichicon UUX1H470MNT1GS, ESR = 0.4 Sanyo 16CV470GX, ESR = 0.17 General Instruments SS16 Coilcraft DO3316-224, DCR = 0.53
Figure 6. 16V-24V to 12V/0.5A Buck Converter Low-Profile Surface Mount
Figure 9. 16V-24V to 12V/0.5A Buck Converter Low-Cost Surface Mount
April 1998*
4-97

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