June 2001

MIC4690

Micrel

MIC4690

500kHz 1A SuperSwitcherTM Buck Regulator

Final Information

General Description

The MIC4690 SuperSwitcherTM is an easy-to-use, 500kHz
step-down PWM voltage regulator. The MIC4690 achieves
over 1A of continuous output current over a wide input voltage
range in an 8-lead SO (small outline) package.

The high switching frequency of the MIC4690 allows the
smallest surface-mount inductors and capacitors to be used.
Internal compensation ensures fast transient response and a
minimum amount of external components.

The MIC4690 features a power SO-8 package with a special
lead frame that allows over 1A of continuous current. The
MIC4690, housed in an SO-8, can replace larger TO-220 and
TO-263 packages in many applications.

The MIC4690 allows for a high degree of safety. It has a wide
input voltage range of 4V to 34V, allowing for it to be used in
applications where input voltage transients may be present.
Built-in safety features include over-current protection, fre-
quency foldback protection, and thermal shutdown.

The MIC4690 is available in an 8-lead SO package with a
junction temperature range of 40

C to +125

Typical Application

10µH

VIN

GND

SHDN

100µF

3.01k

2.94k

2.5V/1A

MIC4690BM

22µF

10V

SHUTDOWN

ENABLE

Power
SOP-8

5Ð8

20V

2.5V Adjustable Converter

VIN

GND

SHDN

220

3.01k

6.49k

1.8V/1A

MIC4690BM

10V

4V to 30V

(34V Transient)

SHUTDOWN

ENABLE

Power
SOP-8

5Ð8

20V

1.8V Adjustable Converter

Features

· SO-8 package with over 1A output current
· Fixed 500kHz operation
· Wide 4V to 34Vinput voltage range
· Output voltage adjustable to 1.23V
· All surface mount solution
· Internally compensated with fast transient response
· Up to 85% efficiency
· Overcurrent protection
· Frequency foldback short-circuit protection
· Thermal shutdown

Applications

· Simple 1A step-down (buck) regulator
· Replacement of TO-220 and TO-263 designs
· 12V to 5V/3.3V/2.5V/1.8V/1.5V conversion
· 5V to 2.5V/1.8V/1.5V conversion
· On-card switching regulators
· Hard disk drives
· Cable modems
· Positive-to-negative converters
· Simple battery chargers

Micrel, Inc. · 1849 Fortune Drive · San Jose, CA 95131 · USA · tel + 1 (408) 944-0800 · fax + 1 (408) 944-0970 · http://www.micrel.com

SuperSwitcher is a trademark of Micrel, Inc.

June 2001

MIC4690

Micrel

Electrical Characteristics

= 12V, V

OUT

= 5V; I

LOAD

= 500mA; V

SHDN

= 0V, T

= 25

C, unless otherwise noted. Bold values indicate 40

+125

Parameter

Condition

Min

Typ

Max

Units

Feedback Voltage

(

1%)

1.217

1.230

1.243

(

2%)

1.205

1.255

30V, 0.1A

LOAD

1A, V

OUT

= 5V

1.193

1.230

1.267

1.180

1.280

Maximum Duty Cycle

= 1.0V

Quiescent Current

= 1.5V

Standby Quiescent Current

SHDN

= 5V (regulator off)

100

SHDN

= 12V (regulator off)

1.5

Frequency Foldback

= 0V

220

300

KHz

Oscillator Frequency

450

500

550

kHz

Saturation Voltage

OUT

= 1A

1.2

Output Leakage Current

= 30V, V

SHDN

= 5V, V

= 0V

500

= 30V, V

SHDN

= 5V, V

= 1V

Short Circuit Current Limit

= 0V, V

OUT

= 0V, See

Test Circuit

1.3

2.5

3.0

Shutdown Pin Input Logic Level

regulator off

1.5

regulator on

1.25

0.8

Shutdown Pin Input Current

SHDN

= 5V (regulator off)

0.7

SHDN

= 0V (regulator on)

1.5

Thermal Shutdown @ T

160

Note 1.

Exceeding the absolute maximum rating may damage the device.

Note 2.

With input voltages above the operating rating, the device may be damaged if a short-circuit is applied to the output. The device will otherwise
not be damaged up to its absolute maximum voltage rating.

Note 3.

Absolute maximum rating is intended for voltage transients only, prolonged dc operation is not recommended.

Note 4.

Devices are ESD sensitive. Handling precautions recommended.

Note 5.

Measured on 1" square of 1 oz. copper FR4 printed circuit board connected to the device ground leads.

Absolute Maximum Ratings

(Note 1)

Supply Voltage (V

), Note 3 ...................................... +34V

Shutdown Voltage (V

SHDN

) ............................. 0.3V to V

Steady-State Output Switch Voltage (V

) ....... 1V to V

Feedback Voltage (V

) .............................................. +12V

Storage Temperature (T

) ....................... 65

C to +150

ESD Rating .............................................................. Note 4

Operating Ratings

(Note 2)

Supply Voltage (V

) ....................................... +4V to +30V

Junction Temperature Range (T

) ........... 40

C to +125

Package Thermal Resistance

(

), Note 5 ........................................................ 63

C/W

(

), ................................................................... 20

C/W

June 2001

MIC4690

Micrel

Typical Characteristics

1.223

1.225

1.227

1.229

1.231

1.233

1.235

1.237

1.239

1.241

1.243

-40 -20 0 20 40 60 80 100120140

VOLTAGE (V)

TEMPERTURE (

Reference Voltage

vs. Temperature

= 12V

OUT

= 5V

OUT

= 100mA

7.6

7.7

7.8

7.9

8.1

8.2

8.3

8.4

8.5

8.6

-40 -20 0 20 40 60 80 100120140

CURRENT (mA)

TEMPERATURE (

Quiescent Current

vs. Temperature

= 12.0V

OUT

= 5.0V

OUT

= 0

10 15 20 25 30 35 40

EFFICIENCY (%)

INPUT VOLTAGE (V)

Efficiency

vs. Input Voltage

OUT

= 5V

OUT

= 1A

100

200

300

400

500

600

-50

100

150

FREQUENCY (kHz)

Temperature (

Frequency vs.

Temperature

= 12V

OUT

= 5V

OUT

= 100mA

100

150

200

250

300

-50

100

150

FREQUENCY (kHz)

Temperature (

Frequency Foldback

vs. Temperature

= 12V

OUT

= 5V

OUT

= 100mA

5.000

5.005

5.010

5.015

5.020

5.025

0.2 0.4 0.6 0.8

1.2 1.4

OUTPUT VOLTAGE (V)

OUTPUT CURRENT (A)

Load Regulation

= 12V

OUT

= 5V

4.96

4.98

5.00

5.02

5.04

5.06

10 15 20 25 30 35 40

OUTPUT VOLTAGE (V)

INPUT VOLTAGE (V)

Line Regulation

= 12V

OUT

= 5V

OUT

= 500mA

0.5

1.0

1.5

2.0

2.5

3.0

3.5

-40 -20 0 20 40 60 80 100120140

SHUTDOWN CURRENT (

TEMPERATURE (

Shutdown Current

vs. Temperature

SHDN

= V

= 12V

OUT

= 5V

0.2

0.4

0.6

0.8

1.2

1.4

1.6

-40

120

160

SHUTDOWN PIN VOLTAGE (V)

TEMPERATURE (

Shutdown Hysteresis

vs. Temperature

OFF

= 12.0V

OUT

= 5.0V

OUT

= 100mA

0.2 0.4 0.6 0.8

1.2 1.4

EFFICIENCY (%)

OUTPUT CURRENT (A)

Efficiency vs.

Output Current

= 12.0V

OUT

= 5.0V

June 2001

MIC4690

Micrel

Block Diagrams

OUT

MIC4690 [adj.]

Internal

Regulator

SHDN

500kHz

Oscillator

Thermal

Shutdown

Reset

Current

Limit

Com-

parator

Error

Amp

Driver

1.23V
Bandgap
Reference

R1 R2

1.23V

OUT

REF

OUT

REF

Adjustable Regulator

Functional Description

The MIC4690 is a variable duty cycle switch-mode regulator
with an internal power switch. Refer to the block diagrams.

Supply Voltage

The MIC4690 operates from a +4V to +30V (transients to
34V) unregulated input. Highest efficiency operation is from
a supply voltage around +12V. See the efficiency curve on
page 5.

Enable/Shutdown

The shutdown (

SHDN

) input is TTL compatible. A logic-low

enables the regulator. A logic-high shuts down the internal
regulator which reduces the current to typically 1.5

A when

SHDN

= V

= 12V and 30

A when V

SHDN

= 5V. See

"Shutdown Input Behavior: Shutdown Hysteresis."

Feedback

Fixed-voltage versions of the regulator have an internal
resistive divider from the feedback (

) pin. Connect

directly to the output voltage.

Adjustable versions require an external resistive voltage
divider from the output voltage to ground, center tapped to the

pin. See Figure 1b for recommended resistor values.

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 500kHz 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 com-
parator output. A lower feedback voltage increases the duty
cycle. The MIC4690 uses a voltage-mode control architec-
ture.

Output Switching

When the internal switch is ON, an increasing current flows
from the supply V

IN,

through external storage inductor L1, to

output capacitor C

OUT

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 C

OUT

Output Capacitor

External output capacitor C

OUT

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.

MIC4690

Micrel

MIC4690

June 2001

Applications Information

Adjustable Regulators

Adjustable regulators require a 1.23V feedback signal. Rec-
ommended voltage-divider resistor values for common out-
put voltages are included in Figure 1b.

For other voltages, the resistor values can be determined
using the following formulas:

R1 R2

1.23V

OUT

REF

OUT

REF

VIN

GND

SHDN

220

10V

3.01k

1.27k

40V

5.0V/1A

MIC4690BM

35V

+6.8V to +30V

SHUTDOWN

ENABLE

5Ð8

Power

SOP-8

Figure 1a. Adjustable Regulator Circuit

Bill of Material Matrix

OUT

(1)

OUT

5.0V

3.01k

976

6.8V-30V

F, 35V

2A, 40V

220

F, 10V

see SOA

Vishay-Dale

Schotty

Sumida

Vishay-Dale

595D226X0035D2T

SS24

CDRH6D38-180ML

594D227X0010D2T

Micro Commercial

5.0V

3.01k

976

6.8V-14V

F, 20V

2A, 20V

100

F, 6.3V

1.0A

Vishay-Dale

Schotty

Sumida

Vishay-Dale

595D476X0020C2T

SS22

CDRH6D38-180ML

595D107X06R3C2T

Micro Commercial

3.3V

3.01k

1.78k

4.9V-14V

F, 20V

2A, 20V

120

F, 4.0V

1.0A

Vishay-Dale

Schotty

Sumida

Vishay-Dale

595D476X0020C2T

SS22

CDRH6D38-150ML

595D127X0004C2T

Micro Commercial

2.5V

3.01k

2.94k

4.25V-14V 47

F, 20V

2A, 20V

120

F, 4.0V

1.0A

Vishay-Dale

Schotty

Sumida

Vishay-Dale

595D476X0020C2T

SS22

CDRH6D38-100ML

595D127X0004C2T

Micro Commercial

1.8V

3.01k

6.49k

4.0V-14V

F, 20V

2A, 20V

120

F, 4.0V

1.0A

Vishay-Dale

Schotty

Sumida

Vishay-Dale

595D476X0020C2T

SS22

CDRH6D38-100ML

595D127X0004C2T

Micro Commercial

Note 1.

All resistors 1%

Figure 1b. Recommended Components for Common Ouput Voltages

June 2001

MIC4690

Micrel

When designing with the MIC4690, it is a good practice to
connect pins 5 through 8 to the largest ground plane that is
practical for the specific design.

Checking the Maximum Junction Temperature:

For this example, with an output power (P

OUT

) of 5W, (5V

output at 1A maximum with V

= 12V) and 50

C maximum

ambient temperature, what is the maximum junction tem-
perature?

Referring to the "Typical Characteristics: 5V Output Effi-
ciency" graph, read the efficiency (

) for 1A output current at

= 12V or perform you own measurement.

= 75%

The efficiency is used to determine how much of the output
power (P

OUT

) is dissipated in the regulator circuit (P

P =

OUT

P =

0.75

= 1.67W

A worst-case rule of thumb is to assume that 80% of the total
output power dissipation is in the MIC4690 (P

D(IC)

) and 20%

is in the diode-inductor-capacitor circuit.

D(IC)

= 0.8 P

D(IC)

= 0.8

1.67W

D(IC)

= 1.336W

Calculate the worst-case junction temperature:

= P

D(IC)

+ (T

) + T

A(max)

where:

= MIC4690 junction temperature

D(IC)

= MIC4690 power dissipation

= junction-to-case thermal resistance.

The

for the MIC4690's power-SOP-8 is approximately

C/W.

= "pin" temperature measurement taken at the

entry point of pins 6 or 7

= ambient temperature

A(max)

= maximum ambient operating temperature

for the specific design.

Calculating the maximum junction temperature given a
maximum ambient temperature of 50

= 1.336W

C/W + (63

C 25

C) + 50

= 114.72

This value is within the allowable maximum operating junc-
tion temperature of 125

C as listed in "Operating Ratings."

Typical thermal shutdown is 160

C and is listed in "Electrical

Characteristics."

Layout Considerations

Layout is very important when designing any switching regu-
lator. Rapidly changing currents through the printed circuit
board traces and stray inductance can generate voltage
transients which can cause problems.

AMBIENT

printed circuit board

ground plane

heat sink area

SOP-8

Figure 2. Power SOP-8 Cross Section

Thermal Considerations

The MIC4690 SuperSwitcherTM features the power-SOP-8.
This package has a standard 8-lead small-outline package
profile, but with much higher power dissipation than a stan-
dard SOP-8. Micrel's MIC4690 SuperSwitcherTM family are
the first dc-to-dc converters to take full advantage of this
package.

The reason that the power SOP-8 has higher power dissipa-
tion (lower thermal resistance) is that pins 5 through 8 and the
die-attach paddle are a single piece of metal. The die is
attached to the paddle with thermally conductive adhesive.
This provides a low thermal resistance path from the junction
of the die to the ground pins. This design significantly im-
proves package power dissipation by allowing excellent heat
transfer through the ground leads to the printed circuit board.

One limitation of the maximum output current on any MIC4690
design is the junction-to-ambient thermal resistance (

) of

the design (package and ground plane).

Examining

in more detail:

= (

)

where:

= junction-to-case thermal resistance

= case-to-ambient thermal resistance

is a relatively constant 20

C/W for a power SOP-8.

is dependent on layout and is primarily governed by the

connection of pins 5 though 8 to the ground plane. The
purpose of the ground plane is to function as a heat sink.

is ideally 63

C/W, but will vary depending on the size of

the ground plane to which the power SOP-8 is attached.

Determining Ground-Plane Heat-Sink Area

There are two methods of determining the minimum ground
plane area required by the MIC4690.

Quick Method

Make sure that MIC4690 pins 5 though 8 are connected to a
ground plane with a minimum area of 6cm

. This ground

plane should be as close to the MIC4690 as possible. The
area may be distributed in any shape around the package or
on any pcb layer

as long as there is good thermal contact to

pins 5 though 8. This ground plane area is more than
sufficient for most designs.

MIC4690

Micrel

MIC4690

June 2001

Load

VIN

GND

SHDN

OUT

MIC4690BM

GND

+4V to +30V

(34V transients)

Power
SOP-8

5 6 7 8

Figure 5. Critical Traces for Layout

GND

SHDN

40V

OUT

GND

U1 MIC4690BM

0.1

50V

35V

4V to +30V

(34V transients)

GND

SOP-8

5Ð8

JP1

OFF

220

10V

C3* 1800pF / 50V

optional

0.1

50V

3.01k

6.49k

JP2a

1.8V

optional

2.94k

1.78k

976½

JP2b

2.5V

JP2c

3.3V

JP2d

5.0V

* C3 can be used to provide additional stability

and improved transient response.

Figure 6a. Evaluation Board Schematic Diagram

To minimize stray inductance and ground loops, keep trace
lengths, indicated by the heavy lines in Figure 5, as short as
possible. For example, keep D1 close to pin 3 and pins 5
through 8, keep L1 away from sensitive node FB, and keep
C

close to pin 2 and pins 5 though 8. See "Applications

Information: Thermal Considerations" for ground plane lay-
out.

The feedback pin should be kept as far way from the switching
elements (usually L1 and D1) as possible.

A circuit with sample layouts are provided. See Figures 6a
though 6e. Gerber files are available upon request.

June 2001

MIC4690

Micrel

Abbreviated Bill of Material (Critical Components)

Reference

Part Number

Manufacturer

Description

Qty

595D2260035D2T

Vishay Sprague

F, 35V

ECE-A1HFS470

Panasonic

F, 50V, 8mm X 11.5mm

TPSD226M035R0300

AVX

F, 35V

C2, C6

VJ0805Y104KXAMB

Vishay Vitramon

0.1

F 50V

594D227X0010D2T

Vishay Sprague

220

F, 10V

SS24

Micro Commercial Corp

Schottky 2A, 40A

B240A

Diode Inc

CDRH6D38-180MC

Sumida

H, 1.5A I

SAT

MIC4690BM

Micrel Semiconductor

1A 200kHz power-SO-8 buck regulator

Vishay Dale, Inc., tel: 1 877-847-4291,

http://www.vishay.com

Diodes Inc, tel: (805) 446-4800,

http://www.diodes.com

Micro Commercial Corp., tel: (800) 346-3371

Sumida, tel: (408) 982-9960,

http://www.sumida.com

Micrel, tel: (408) 944-0800,

http://www.micrel.com

Printed Circuit Board Layouts

Figure 6b. Top-Side Silk Screen

Figure 6c. Top-Side Copper

Figure 6d. Bottom-Side Silk Screen

Figure 6e. Bottom-Side Copper

MIC4690

Micrel

MIC4690

June 2001

MICREL INC.

1849 FORTUNE DRIVE

SAN JOSE, CA 95131

USA

TEL

+ 1 (408) 944-0800

FAX

+ 1 (408) 944-0970

WEB

http://www.micrel.com

This information is believed to be accurate and reliable, however no responsibility is assumed by Micrel for its use nor for any infringement of patents or

other rights of third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent right of Micrel Inc.

Package Information

0.244 (6.20)
0.228 (5.79)

0.197 (5.0)
0.189 (4.8)

SEATING

PLANE

0.026 (0.65)

MAX

)

0.010 (0.25)
0.007 (0.18)

0.064 (1.63)
0.045 (1.14)

0.0098 (0.249)
0.0040 (0.102)

0.020 (0.51)
0.013 (0.33)

0.157 (3.99)
0.150 (3.81)

0.050 (1.27)

TYP

PIN 1

DIMENSIONS:

INCHES (MM)

0.050 (1.27)
0.016 (0.40)

8-Lead SOP (M)

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