Datasheet MIC4574 Datasheet (MICREL)

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 200µA
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

• < 200µA 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

6V to 24V

10µF

C1

35V

Shutdown
Enable

8V to 24V

C1

47µF

35V

5

SHDN

MIC4574BWM

10

V

IN

SGND

SHDN

MIC4574-5.0BN

5

V

IN

SGND

24

SW

PGND

Fixed Regulator

12

SW

3

FB

PGND

64

Adjustable Regulator

73

100µH

1

FB

D1
1N5819

L1

100µH

D1

MBRS130LT3

L1

R2

2.49k
1%

R1

1.50k
1%

5.0V/0.5A

C2
220µF
16V

C3
3300pF

3.3V/0.5A

C2
330µF

6.3V

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MIC4574 Micrel

Ordering Information

Part Number Voltage Temperature Range Package

MIC4574-3.3BN 3.3V –40°C to +85°C 8-pin DIP
MIC4574-5.0BN 5.0V –40°C to +85°C 8-pin DIP
MIC4574BN Adjustable –40°C to +85°C 8-pin DIP
MIC4574-3.3BWM 3.3V –40°C to +85°C 14-lead SOIC
MIC4574-5.0BWM 5.0V –40°C to +85°C 14-lead SOIC
MIC4574BWM Adjustable –40°C to +85°C 14-lead SOIC

Pin Configuration

1NC NC14

2NC NC13
3FB SW12

FB
SGND
SHDN
PGND

NC

1
2
3
4

8

SW

7

NC

6

V

5

IN

4SGND NC11
5SHDN V
6PGND NC9
7NC NC8

10

8-Pin DIP (N) 14-Lead Wide SOIC (WM)

Pin Description

Pin Number Pin Number Pin Name Pin Function

N Package WM Package

1 NC Not internally connected. Solder to printed circuit for maximum heat transfer.
2 NC Not internally connected. Solder to printed circuit for maximum heat transfer.

1 3 FB 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.
2 4 SGND Signal Ground
3 5 SHDN Shutdown (Input): Logic low enables regulator. Logic high (> 2.4V) shuts

down regulator.
4 6 PGND Power Ground

7 NC Not internally connected. Solder to printed circuit for maximum heat transfer.
8 NC Not internally connected. Solder to printed circuit for maximum heat transfer.
9 NC Not internally connected. Solder to printed circuit for maximum heat transfer.

510 VINSupply Voltage (Input): Unregulated +4V to +24V supply voltage.

11 NC Not internally connected. Solder to printed circuit for maximum heat transfer.

7 12 SW Switch (Output): Emitter of NPN output switch. Connect to external storage

inductor and Shottky diode.
8 13 NC Not internally connected. Solder to printed circuit for maximum heat transfer.

14 NC Not internally connected. Solder to printed circuit for maximum heat transfer.

IN

4

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MIC4574 Micrel

Absolute Maximum Ratings

Supply Voltage (VIN) Note 1 .......................................+40V

Shutdown (V

Output Switch (VSW) steady state.................................–1V

Junction Temperature (TJ) ...................................... +150°C

) ....................................... –0.3V to +36V

SHDN

Operating Ratings

Supply Voltage (VIN) ...................................................+24V

Package Thermal Resistance

θJA Plastic DIP ..................................................130°C/W

θJC SOIC ...........................................................120°C/W

Storage Temperature ............................... –65°C to +150°C

Electrical Characteristics

VIN =12V; I

Parameter Condition Min Typ Max Units
MIC4574 [Adjustable]

Feedback Voltage 1.217 1.230 1.243 V
Feedback Voltage 8V ≤ V

Efficiency I
Feedback Bias Current 50 100 nA

MIC4574-3.3

Output Voltage 3.234 3.3 3.366 V
Output Voltage 6V ≤ V

Efficiency 72 %

MIC4574-5.0

Output Voltage 4.900 5.0 5.100 V
Output Voltage 8V ≤ V

Efficiency 77 %

MIC4574 / -3.3 / -5.0

Oscillator Frequency 180 200 220 kHz
Saturation Voltage I

Maximum Duty Cycle (On) FB connected to 0V 90 95 %
Current Limit Peak Current, t

Output Leakage Current V

Quiescent Current 510mA
Standby Quiescent Current SHDN = 5V (regulator off) 50 200 µA
SHDN Input Logic Level V

SHDN Input Current SHDN = 5V (regulator off) 4 30 µA

= 100mA; TA = 25°C, bold values indicate –40°C ≤ TA ≤ +85°C; unless noted

LOAD

≤ 24V, 0.1A ≤ I

IN

= 0.5A, V

LOAD

≤ 24V, 0.1A ≤ I

IN

≤ 24V, 0.1A ≤ I

IN

= 0.5A 1 1.3 V

OUT

= 24V, FB connected to 6V

IN

= 5V 77 %

OUT

≤ 3µs 0.7 1.0 1.6 A

ON

≤ 0.5A 1.193 1.230 1.267 V

LOAD

≤ 0.5A 3.168 3.3 3.432 V

LOAD

≤ 0.5A 4.800 5.0 5.200 V

LOAD

Output = 0V 0 2 mA
Output = –1V 7.5 30 mA

= 0V (regulator off) 2.2 1.4 V

OUT

= 3.3V or 5V (regulator on) 1.2 1.0 V

V

OUT

SHDN = 0V (regulator on) –10 0.01 10 µA

1.180 1.280 V

500 nA

3.135 3.465 V

4.750 5.250 V

1.5 V

0.65 1.8 A

2.4 V

0.8 V

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.

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MIC4574 Micrel

Block Diagrams

+24V max.

V

Shutdown
Enable

SHDN

Internal

Regulator

200kHz

Oscillator

Thermal

Shutdown

Current

Limit

IN

C

IN

Shutdown
Enable

SHDN

Driver

1.23V

Bandgap

R1

R2
GND

0.5A
Switch

MIC4574-x.x

Com-

parator

Error
Amp.

Block Diagram with External Components

Fixed Step-Down Regulator

+24V max.

V

IN

Internal

Regulator

200kHz

Oscillator

MIC4574

Com-

parator

[Adjustable]

Thermal

Shutdown

Error
Amp.

Driver

1.23V

Bandgap

Current

Limit

GND

0.5A
Switch

SW

FB

SW

FB

L1

D1

C

IN

V

OUT VREF

R1 R2

L1

D1

R1

R2

V

OUT

C

OUT

4

R1

+ 1

R2

V

OUT

1

V

REF

V

OUT

C

OUT

Block Diagram with External Components

Adjustable Step-Down Regulator

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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 50µA.

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 V
output capacitor C

through external storage inductor L1, to

IN,

and the load. Energy is stored in the

OUT

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

provides stabilization and

OUT

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

100µH

C1

33µF

63V

3.3V/0.5A

C2
220µF
16V

3

SHDN

MIC4574BN

5

V

IN

SGND

PGND

73

PGND

SW

FB

1

D1
1N5819

6V to 24V

C1

47µF

35V

SHDN

MIC4574-3.3BN

5

V

IN

SGND

24

C1 Nichicon UPL1V470MEH, ESR = 0.34Ω
C2 Nichicon UPL1C221MPH, ESR = 0.16Ω
D1 Motorola 1N5819
L1 Sumida RCH875-101K, DCR = 0.28Ω

Figure 1. 6V–24V to 3.3V/0.5A Buck Converter

Through Hole

16V to 24V

For a mathematical approach to component selection and
circuit design, refer to Application Note 14.

L1

5.0V/0.5A

100µH

8V to 24V

C1

47µF

35V

73

PGND

SW

FB

1

D1
1N5819

SHDN

MIC4574-5.0BN

5

V

IN

SGND

24

C1 Nichicon UPL1J470MEH, ESR = 0.34Ω
C2 Nichicon UPL1C221MPH, ESR = 0.16Ω
D1 Motorola 1N5819
L1 Sumida RCH875-101K, DCR = 0.28Ω

Figure 2. 8V–24V to 5V/0.5A Buck Converter

Through Hole

SW

FB

42

7

1

L1

220µH

MBR160

R2

13.0k
1%

R1

1.50k
1%

12V/0.5A

C2
220µF
16V

C2
220µF
16V

C1 Nichicon UPL1J330MEH, ESR = 0.35Ω
C2 Nichicon UPL1C221MPH, ESR = 0.16Ω
D1 Motorola MBR160
L1 Sumida RCH106-221K, DCR = 0.78Ω

Figure 3. 16V–24V to 12V/0.5A Buck Converter

Through Hole

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MIC4574 Micrel

C1

68µF

35V

D1
MBRS130LT3

C2
470µF
16V

L1

100µH

SGND

FB

SW

MIC4574-3.3BWM

SHDN

6V to 24V

3.3V/0.5A

V

IN

C1 Sanyo 35CV168GX, ESR = 0.34Ω
C2 Sanyo 16CV470GX, ESR = 0.17Ω
D1 Motorola MBRS130LT3
L1 Coilcraft DO3316P-104, DCR = 0.23Ω

PGND

46

3

125

10

C1

68µF

35V

D1
MBRS130LT3

C2
470µF
16V

L1

100µH

SGND

FB

SW

MIC4574-5.0BWM

SHDN

8V to 24V

5V/0.5A

V

IN

C1 Sanyo 35CV168GX, ESR = 0.34Ω
C2 Sanyo 16CV470GX, ESR = 0.17Ω
D1 Motorola MBRS130LT3
L1 Coilcraft DO3316P-104, DCR = 0.23Ω

PGND

46

3

125

10

SW

FB

64

12

100µH

3

D1

R2

2.49k
1%

R1

1.50k
1%

6V to 24V

C1

10µF

35V

5

SHDN

MIC4574BWM

10

V

IN

SGND

PGND

L1

MBRS130LT3

C1 AVX TPSD106M035R0300, ESR = 0.3Ω
C2 AVX TPSE337M006R0100, ESR = 0.1Ω
D1 Motorola MBRS130LT3
L1 Coiltronics CTX100-2P, DCR = 0.541Ω

Figure 4. 6V–24V to 3.3V/0.5A Buck Converter

Low-Profile Surface Mount

SW

FB

64

12

100µH

3

D1

R2

3.01k
1%

R1

1.00k
1%

8V to 24V

C1

10µF

35V

5

SHDN

MIC4574BWM

10

V

IN

SGND

PGND

L1

MBRS130LT3

C1 AVX TPSD106M035R0300, ESR = 0.3Ω
C2 AVX TPSE227M010R0100, ESR = 0.1Ω
D1 Motorola MBRS130LT3
L1 Coiltronics CTX100-2P, DCR = 0.541Ω

Figure 5. 8V–24V to 5V/0.5A Buck Converter

Low-Profile Surface Mount

C3
3300pF

C3
3300pF

3.3V/0.5A

C2
330µF

6.3V

5V/0.5A

C2
220µF
10V

Figure 7. 6V–24V to 3.3V/0.5A Buck Converter

Low-Cost Surface Mount

Figure 8. 8V–24V to 5V/0.5A Buck Converter

Low-Cost Surface Mount

4

SW

FB

64

12

250µH

3

D1
SS16

R2

13.0k
1%

R1

1.50k
1%

16V to 24V

C1

10µF

50V

5

SHDN

MIC4574BWM

10

V

IN

SGND

PGND

C1 Tokin C55Y5U1H106Z
C2 AVX TPSE686M020R0150, ESR = 0.15Ω
D1 General Instruments SS16
L1 Coiltronics CTX250-4P, DCR = 0.434Ω

L1

Figure 6. 16V–24V to 12V/0.5A Buck Converter

Low-Profile Surface Mount

C3
3300pF

12V/0.5A

C2
68µF
20V

SW

FB

64

12

220µH

3

D1
SS16

R2

13.0k
1%

R1

1.50k
1%

16V to 24V

C1

47µF

50V

5

SHDN

MIC4574BWM

10

V

IN

SGND

PGND

C1 Nichicon UUX1H470MNT1GS, ESR = 0.4Ω
C2 Sanyo 16CV470GX, ESR = 0.17Ω
D1 General Instruments SS16
L1 Coilcraft DO3316-224, DCR = 0.53Ω

L1

Figure 9. 16V–24V to 12V/0.5A Buck Converter

Low-Cost Surface Mount

12V/0.5A

C2
470µF
16V

April 1998• 4-97