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MIC4680

1A 200kHz SuperSwitcher™

Buck Regulator

SuperSwitcher is a trademark of Micrel, Inc.

Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com

March 2008

M9999-032808

General Description

The MIC4680 SuperSwitcher™ is an easy-to-use fixed or

adjustable output voltage step-down (buck) switch-mode

voltage regulator. The 200kHz MIC4680 achieves up to

1.3A of continuous output current over a wide input range

in a 8-pin SOIC.

The MIC4680 is available in 3.3V and 5V fixed output

versions or adjustable output down to 1.25V.

The MIC4680 has an input voltage range of 4V to 34V,

with excellent line, load, and transient response. The

regulator performs cycle-by-cycle current limiting and

thermal shutdown for protection under fault conditions. In

shutdown mode, the regulator draws less than 2µA of

standby current.

The MIC4680 SuperSwitcher™ regulator requires a mini-

mum number of external components and can operate

using a standard series of inductors and capacitors.

Frequency compensation is provided internally for fast

transient response and ease of use.

The MIC4680 is available in the 8-pin SOIC with a

–40°C to +125°C junction temperature range.

Features

• SOIC-8 package with up to 1.3A output current

• All surface mount solution

• Only 4 external components required

• Fixed 200kHz operation

• 3.3V, 5V, and adjustable output versions

• Internally compensated with fast transient response

• Wide 4V to 34V operating input voltage range

• Less than 2µA typical shutdown-mode current

• Up to 90% efficiency

• Thermal shutdown

• Overcurrent protection

Applications

• Simple 1A high-efficiency step-down (buck) regulator

• Replacement of TO-220 and TO-263 designs

• Efficient pre-regulator (5V to 2.5V, 12V to 3.3V, etc.)

• On-card switching regulators

• Positive-to-negative converter (inverting buck-boost)

• Simple battery charger

• Negative boost converter

• Higher output current regulator using external FET

Typical Application

68µH

GND

SHDN

220µF

16V

B260A or

SS26

3.3V/1A

MIC4680-3.3BM

15µF

35V

+6V to +34V

SHUTDOWN

ENABLE

5–8

Power

SOIC-8

68µH

GND

SHDN

220µF

16V

3.01k

2.94k

2.5V/1A

MIC4680BM

15µF

35V

+5V to +34V

SHUTDOWN

ENABLE

Power

SOIC-8

5–8

B260A or

SS26

Fixed Regulator Circuit

Adjustable Regulator Circuit

Summary of content (15 pages)

PAGE 1
MIC4680 1A 200kHz SuperSwitcher™ Buck Regulator General Description Features The MIC4680 SuperSwitcher™ is an easy-to-use fixed or adjustable output voltage step-down (buck) switch-mode voltage regulator. The 200kHz MIC4680 achieves up to 1.3A of continuous output current over a wide input range in a 8-pin SOIC. The MIC4680 is available in 3.3V and 5V fixed output versions or adjustable output down to 1.25V.
PAGE 2
Micrel, Inc. MIC4680 Ordering Information Part Number Standard Pb-Free Voltage Junction Temp. Range Package MIC4680BM MIC4680YM Adj. –40°C to +125°C 8-Pin SOIC MIC4680-3.3BM MIC4680-3.3YM 3.3V –40°C to +125°C 8-Pin SOIC MIC4680-5.0BM MIC4680-5.0YM 5.0V –40°C to +125°C 8-Pin SOIC Pin Configuration SHDN 1 8 GND IN 2 7 GND SW 3 6 GND FB 4 5 GND 8-Pin SIOC (M) Pin Description Pin Number Pin Name 1 SHDN 2 VIN Supply Voltage (Input): Unregulated +4V to +34V supply voltage.
PAGE 3
Micrel, Inc. MIC4680 Absolute Maximum Ratings(1) Operating Ratings(2) Supply Voltage (VIN)(3) ..................................................+38V Shutdown Voltage (VSHDN)............................. –0.3V to +38V Steady-State Output Switch Voltage (VSW) ....................–1V Feedback Voltage [Adjustable] (VFB) ...........................+12V Storage Temperature (Ts) .........................–65°C to +150°C EDS Rating(5) Supply voltage (VIN)(4).......................................
PAGE 4
Micrel, Inc. MIC4680 Parameter Condition Min Typ Shutdown Input Logic Level regulator off 2 1.6 1.0 0.8 V VSHDN = 5V (regulator off) –10 –0.5 10 µA VSHDN = 0V (regulator on) –10 –1.5 10 µA regulator on Shutdown Input Current Thermal Shutdown 160 Max Units V °C Notes: 1. Exceeding the absolute maximum rating may damage the device. 2. The device is not guaranteed to function outside its operating rating. 3.
PAGE 5
Micrel, Inc. MIC4680 Typical Characteristics 4.99 4.98 4.97 4.96 3.5 3.0 5 10 15 20 25 30 INPUT VOLTAGE (V) 2.0 1.5 1.0 210 200 190 180 -50 -25 0 25 50 75 100 125 TEMPERATURE (°C) 80 4 3 2 1 VIN = 12V 1.236 1.234 1.232 VIN = 12V VOUT = 5V IOUT = 1A 1.230 1.228 -50 -25 0 25 50 75 100 125 150 TEMPERATURE (°C) 40 30 20 10 70 60 12V 24V 7V 50 40 30 20 10 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 OUTPUT CURRENT (A) March 2008 0 0 0.2 0.4 0.6 0.8 1.0 1.2 1.
PAGE 6
Micrel, Inc. MIC4680 Safe Operating Area 1.5 Minimum Current Limit 1.4 1.3 1.2 Note OUTPUT CURRENT (A) 1.1 1.0 0.9 0.8 0.7 0.6 0.5 0.4 VOUT = 5V TA = 60°C Demonstration board layout 0.3 0.2 0.1 0 0 5 10 15 20 25 INPUT VOLTAGE (V) 30 35 Functional Characteristics Frequency Foldback The MIC4680 folds the switching frequency back during a hard short-circuit condition to reduce the energy per cycle and protect the device.
PAGE 7
Micrel, Inc. MIC4680 Bode Plots The following bode plots show that the MIC4680 is stable over all conditions using a 68µF inductor (L) and a 220µF output capacitor (COUT). To assure stability, it is a good practice to maintain a phase margin of greater than 35°.
PAGE 8
Micrel, Inc. MIC4680 Functional Diagrams V IN IN SHDN Internal Regulator 200kHz Oscillator Thermal Shutdown Current Limit Comparator VOUT SW Driver Reset 1A Switch COUT FB Error Amp 1.23V Bandgap Reference MIC4680-x.x GND Fixed Regulator VIN IN SHDN Internal Regulator 200kHz Oscillator Thermal Shutdown ⎛ R1 ⎞ VOUT = VREF ⎜ + 1⎟ ⎝ R2 ⎠ ⎛V ⎞ R1 = R2 ⎜ OUT - 1⎟ ⎝ VREF ⎠ Current Limit VREF = 1.23V Comparator VOUT SW Driver Reset 1A Switch COUT R1 FB Error Amp 1.
PAGE 9
Micrel, Inc. MIC4680 Functional Description 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. The MIC4680 uses a voltagemode control architecture. The MIC4680 is a variable duty cycle switch-mode regulator with an internal power switch.
PAGE 10
Micrel, Inc. MIC4680 Applications Information Adjustable Regulators Adjustable regulators require a 1.23V feedback signal. Recommended voltage-divider resistor values for common output voltages are included in Figure 1b.
PAGE 11
Micrel, Inc. MIC4680 Thermal Considerations The MIC4680 SuperSwitcher features the power-SOIC8. This package has a standard 8-pin small-outline package profile but with much higher power dissipation than a standard SOIC-8. The MIC4680 SuperSwitcher is the first dc-to-dc converter to take full advantage of this package. The reason that the power SOIC-8 has higher power dissipation (lower thermal resistance) is that pins 5 though 8 and the die-attach paddle are a single piece of metal.
PAGE 12
Micrel, Inc. MIC4680 POUT − POUT η PD = 5W − 5W 0.79 Layout Considerations Layout is very important when designing any switching regulator. Rapidly changing switching currents through the printed circuit board traces and stray inductance can generate voltage transients which can cause problems. To minimize stray inductance and ground loops, keep trace lengths, indicated by the heavy lines in Figure 5, as short as possible.
PAGE 13
Micrel, Inc. MIC4680 Printed Circuit Board Layouts Figure 6b. Top-Side Silk Screen Figure 6d. Bottom-Side Silk Screen Figure 6c. Top-Side Copper Figure 6e. Bottom-Side Copper Abbreviated Bill of Materials (Critical Components) Reference Part Number Manufacturer Description C1 TPSD156M035R0300 AVX1 15µF 35V 2 Qty. 1 ECE-A1HFS470 Panasonic C4 TPSD227M010R0150 AVX 220µF 10V 1 D1 B260A Vishay-Diodes, Inc.3 Schottky 1 SS26 General Semiconductor UP2B-680 Coiltronics4 68µH, 1.
PAGE 14
Micrel, Inc. MIC4680 Application Circuits For continuously updated circuits using the MIC4680, see Application Hint 37 at www.micrel.com. J1 +34V max. Figure 7. Constant Current and Constant Voltage Battery Charger Figure 8. +12V to –12V/150mA Buck-Boost Converter +4.5V to +17V U1 MIC4680BM MIC4417BM4 2 1 IN SHDN SW 3 FB 4 Si4425DY 3.3V/5A GND SOIC-8 5–8 * I SAT = 8A GND Figure 9. 5V to 3.
PAGE 15
Micrel, Inc. MIC4680 Package Information 8-Pin SOIC (M) 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.