MAXIM MAX8576, MAX8579 User Manual

General Description

The MAX8576–MAX8579 synchronous PWM buck con­trollers use a hysteretic voltage-mode control algorithm
to achieve a fast transient response without requiring
loop compensation. The MAX8576/MAX8577 contain an
internal LDO regulator allowing the controllers to func­tion from only one 3V to 28V input supply. The
MAX8578/MAX8579 do not contain the internal LDO
and require a separate supply to power the IC when the
input supply is higher than 5.5V. The MAX8576–
MAX8579 output voltages are adjustable from 0.6V to

0.9 x VINat loads up to 15A.

Nominal switching frequency is programmable over the
200kHz to 500kHz range. High-side MOSFET sensing is
used for adjustable hiccup current-limit and short-cir­cuit protection. The MAX8576/MAX8578 can start up
into a precharged output without pulling the output volt­age down. The MAX8577/MAX8579 have startup output
overvoltage protection (OVP), and will pull down a
precharged output.

Applications

Motherboard Power Supplies

AGP and PCI-Express Power Supplies

Graphic-Card Power Supplies

Set-Top Boxes

Point-of-Load Power Supplies

Features

♦ 3V to 28V Supply Voltage Range

♦ 1.2% Accurate Over Temperature

♦ Adjustable Output Voltage Down to 0.6V

♦ 200kHz to 500kHz Switching Frequency

♦ Adjustable Temperature-Compensated Hiccup

Current Limit

♦ Lossless Peak Current Sensing

♦ Monotonic Startup into Prebias Output

(MAX8576/MAX8578)

♦ Startup Overvoltage Protection

(MAX8577/MAX8579)

♦ Enable/Shutdown

♦ Adjustable Soft-Start

MAX8576–MAX8579

3V to 28V Input, Low-Cost, Hysteretic

Synchronous Step-Down Controllers

________________________________________________________________ Maxim Integrated Products 1

OCSET

IN

DH

LXGND

VL

SS

FB

MAX8576
MAX8577

BST

DL

INPUT
UP TO 28V

OUTPUT

0.6V TO 0.9 x V

IN

Typical Operating Circuit

19-3289; Rev 1; 6/05

For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

EVALUATION KIT

AVAILABLE

Ordering Information

PART

TEMP RANGE

PIN-PACKAGE

MAX8576EUB

10 µMAX

®

MAX8577EUB

10 µMAX

MAX8578EUB

10 µMAX

MAX8579EUB

10 µMAX

Pin Configurations appear at end of data sheet.

µMAX is a registered trademark of Maxim Integrated Products, Inc.

-40°C to +85°C

-40°C to +85°C

-40°C to +85°C

-40°C to +85°C

MAX8576–MAX8579

3V to 28V Input, Low-Cost, Hysteretic
Synchronous Step-Down Controllers

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.

IN to GND (MAX8576/MAX8577) ...........................-0.3V to +30V

VL to GND (MAX8576/MAX8577).............................-0.3V to +6V

IN to VL (MAX8576/MAX8577) ...............................-0.3V to +30V

V

CC

to GND (MAX8578/MAX8579) ..........................-0.3V to +6V

SS to GND (MAX8576/MAX8577) ...............-0.3V to (V

VL

+ 0.3)V

SS to GND (MAX8578/MAX8579)...............-0.3V to (V

CC

+ 0.3)V

DL to GND (MAX8576/MAX8577) ...............-0.3V to (V

VL

+ 0.3)V

DL to GND (MAX8578/MAX8579) ..............-0.3V to (V

CC

+ 0.3)V

BST to GND ............................................................-0.3V to +36V

BST to LX..................................................................-0.3V to +6V

LX to GND .....................-1V (-2.5V for <50ns Transient) to +30V

DH to LX..................................................-0.3V to +(V

BST

+ 0.3)V

FB to GND ................................................................-0.3V to +6V

EN to GND (MAX8578/MAX8679EUB) .....................-0.3V to +6V

OCSET to GND (MAX8576/MAX8677) ........-0.3V to (V

IN

+ 0.3)V

OCSET to GND (MAX8578/MAX8679) ...................-0.3V to +30V

OCSET to LX (MAX8576/MAX8677) ............-0.6V to (V

IN

+ 0.3)V

OCSET to LX (MAX8578/MAX8679) .......................-0.6V to +30V

DH and DL Continuous Current ............................±250mA RMS

Continuous Power Dissipation (T

A

= +70°C)

10-Pin µMAX (derate 5.6mW/°C above +70°C) ...........444mW

Operating Temperature Range ...........................-40°C to +85°C

Junction Temperature......................................................+150°C

Storage Temperature Range .............................-65°C to +150°C

Lead Temperature (soldering, 10s) ................................+300°C

ELECTRICAL CHARACTERISTICS

(VIN= 12V (MAX8576/MAX8577 only), 4.7µF capacitor from VL (MAX8576/MAX8577 only) or VCC(MAX8578/MAX8579 only) to GND;
V

CC

= VEN= 5V (MAX8578/MAX8579 only); 0.01µF capacitor from SS to GND; VFB= 0.65V; V

BST

= 5V; VLX= V

GND

= 0V; V

OCSET

=

11.5V; DH = unconnected; DL = unconnected; T

A

= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)

PARAMETER CONDITIONS

UNITS

SUPPLY VOLTAGES

MAX8576/MAX8577 5.5

IN Supply Voltage

IN = VL (MAX8576/MAX8577) 3.0 5.5

V

VCC Input Voltage MAX8576/MAX8577 3.0 5.5 V

VL Output Voltage IVL = 10mA (MAX8576/MAX8577)

5.0

V

VL Maximum Output Current MAX8576/MAX8577 20 mA

Rising

2.8

Falling 2.4

2.5

V

VL or VCC Undervoltage Lockout
(UVLO)

Hysteresis

mV

VIN = 12V 0.6 2

VIN = VVL = 5V 1.1 3

No switching, VFB = 0.65V
(MAX8576/MAX8577)

V

IN

= VVL = 3.3V 0.6 2

V

CC

= 5V 0.6 2

Supply Current

V

EN

= 0V or VFB = 0.65V, no

switching (MAX8578/MAX8579)

V

CC

= 3.3V 0.6 2

mA

REGULATOR

Output Regulation Accuracy VFB peak

0.6

V

Output Regulation Hysteresis (Note 1)

20

mV

FB falling to DL falling 50

FB Propagation Delay

FB rising to DH falling 70

ns

Overvoltage-Protection (OVP)
Threshold

V

TA = +85°C60

High-Side Current-Sense
Program Current (Note 2)

T

A

= +25°C

50

µA

MIN TYP MAX

4.75

2.75

2.45

350

0.593

12.5

0.70 0.75 0.80

42.5

28.0

5.25

2.90

0.607

28.0

57.5

MAX8576–MAX8579

3V to 28V Input, Low-Cost, Hysteretic

Synchronous Step-Down Controllers

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(VIN= 12V (MAX8576/MAX8577 only), 4.7µF capacitor from VL (MAX8576/MAX8577 only) or VCC(MAX8578/MAX8579 only) to GND;
V

CC

= VEN= 5V (MAX8578/MAX8579 only); 0.01µF capacitor from SS to GND; VFB= 0.65V; V

BST

= 5V; VLX= V

GND

= 0V; V

OCSET

=

11.5V; DH = unconnected; DL = unconnected; T

A

= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)

PARAMETER CONDITIONS

UNITS

High-Side Current-Sense
Overcurrent Trip Adjustment
Range

V

IN

- V

OCSET

V

Soft-Start Internal Resistance 45 80 125 kΩ

Fault Hiccup Internal SS Pulldown
Current

V

LX

< V

OCSET

and VFB < V

SS

nA

DRIVER SPECIFICATIONS

Sourcing current 2.6 4.0

DH Driver Resistance

Sinking current 1.9 3.0

Ω

Sourcing current 2.6 4.0

DL Driver Resistance

Sinking current 1.1 2.0

Ω

Dead Time

DH low to DL high and DL low to DH high
(adaptive)

40 ns

DH Minimum On-Time

245 ns

Normal operation

220

DL Minimum On-Time

Current fault

ns

BST Current V

BST

- VLX = 5.5V, VLX = 28V, VFB < V

SS

mA

EN

Input Voltage Low VCC = 3V (MAX8578/MAX8579) 0.7 V

Input Voltage High VCC = 5.5V (MAX8578/MAX8579) 1.5 V

THERMAL SHUTDOWN

Thermal Shutdown Rising temperature, hysteresis = 20°C (typ)

°C

ELECTRICAL CHARACTERISTICS

(VIN= 12V (MAX8576/MAX8577 only), 4.7µF capacitor from VL (MAX8576/MAX8577 only) or VCC(MAX8578/MAX8579 only) to GND;
V

CC

= VEN= 5V (MAX8578/MAX8579 only); 0.01µF capacitor from SS to GND; VFB= 0.65V; V

BST

= 5V; VLX= V

GND

= 0V; V

OCSET

=

11.5V; DH = unconnected; DL = unconnected; T

A

= -40°C to +85°C, unless otherwise noted. Note 3)

PARAMETER CONDITIONS

UNITS

SUPPLY VOLTAGES

MAX8576/MAX8577 5.5

IN Supply Voltage

IN = VL, MAX8576/MAX8577 3.0 5.5

V

VCC Input Voltage MAX8576/MAX8577 3.0 5.5 V

VL Output Voltage IVL = 10mA, MAX8576/MAX8577

V

VL Maximum Output Current MAX8576/MAX8577 20 mA

MIN TYP MAX

0.05 0.40

250

140

120

580

1.65

+160

MIN TYP MAX

4.75 5.25

28.0

MAX8576–MAX8579

3V to 28V Input, Low-Cost, Hysteretic
Synchronous Step-Down Controllers

4 _______________________________________________________________________________________

Note 1: Guaranteed by design.
Note 2: This current linearly compensates for the MOSFET temperature coefficient.
Note 3: Specifications to -40

°C are guaranteed by design and not production tested.

ELECTRICAL CHARACTERISTICS (continued)

(VIN= 12V (MAX8576/MAX8577 only), 4.7µF capacitor from VL (MAX8576/MAX8577 only) or VCC(MAX8578/MAX8579 only) to GND;
V

CC

= VEN= 5V (MAX8578/MAX8579 only); 0.01µF capacitor from SS to GND; VFB= 0.65V; V

BST

= 5V; VLX= V

GND

= 0V; V

OCSET

=

11.5V; DH = unconnected; DL = unconnected; T

A

= -40°C to +85°C, unless otherwise noted. Note 3)

PARAMETER CONDITIONS

UNITS

Rising

VL or VCC Undervoltage Lockout
(UVLO)

Falling

V

VIN = 12V 2

VIN = VVL = 5V 3.5

No switching, VFB = 0.65V
(MAX8576/MAX8577)

V

IN

= VVL = 3.3V 2

V

CC

= 5V 2

Supply Current

V

EN

= 0V or VFB = 0.65V, no

switching (MAX8578/MAX8579)

V

CC

= 3.3V 2

mA

REGULATOR

Output Regulation Accuracy VFB peak

V

Overvoltage-Protection (OVP)
Threshold

V

High-Side Current-Sense Over­Current Trip Adjustment Range

V

IN

- V

OCSET

V

DRIVER SPECIFICATIONS

Sourcing current 4

DH Driver Resistance

Sinking current 3.0

Ω

Sourcing current 4.0

DL Driver Resistance

Sinking current 2.0

Ω

DH Minimum On-Time

ns

DL Minimum On-Time Normal operation

ns

EN

Input Voltage Low VCC = 3V, MAX8578/MAX8579 0.7 V

Input Voltage High VCC = 5.5V, MAX8578/MAX8579 1.5 V

MIN TYP MAX

2.75 2.90

2.40 2.55

0.591 0.607

0.70 0.80

0.05 0.40

245

220

MAX8576–MAX8579

3V to 28V Input, Low-Cost, Hysteretic

Synchronous Step-Down Controllers

_______________________________________________________________________________________ 5

EFFICIENCY vs. LOAD CURRENT

(CIRCUIT OF FIGURE 2)

MAX8576-79 toc01

LOAD CURRENT (A)

EFFICIENCY (%)

101

10

20

30

40

50

60

70

80

90

100

0

0.1 100

V

OUT

= 3.3V

V

OUT

= 2.5V

V

OUT

= 1.8V

V

OUT

= 1.5V

VIN = 12V

EFFICIENCY vs. LOAD CURRENT

(CIRCUIT OF FIGURE 3)

MAX8576-79 toc02

LOAD CURRENT (A)

EFFICIENCY (%)

1

10

20

30

40

50

60

70

80

90

100

0

0.1 10

V

OUT

= 3.3V

V

OUT

= 2.5V

V

OUT

= 1.8V

V

OUT

= 1.5V

VIN = 12V

LOAD REGULATION

(CIRCUIT OF FIGURE 2)

MAX8576-79 toc03

LOAD CURRENT (A)

OUTPUT VOLTAGE (V)

105

1.76

1.77

1.78

1.79

1.80

1.81

1.82

1.83

1.84

1.75
015

LINE REGULATION

(CIRCUIT OF FIGURE 2)

MAX8576-79 toc04

INPUT VOLTAGE (V)

OUTPUT VOLTAGE (V)

201510

1.80

1.81

1.82

1.83

1.84

1.85

1.79
525

0A LOAD

15A LOAD

LINE REGULATION

(CIRCUIT OF FIGURE 3)

MAX8576-79 toc05

INPUT VOLTAGE (V)

OUTPUT VOLTAGE (V)

201510

1.72

1.74

1.78

1.80

1.82

1.84

1.86

1.70
525

NO LOAD

5A LOAD

1.76

SWITCHING FREQUENCY vs. INPUT

VOLTAGE (CIRCUIT OF FIGURE 3)

MAX8576-79 toc06

INPUT VOLTAGE (V)

SWITCHING FREQUENCY (kHz)

201510

250

300

350

400

500

550

600

200

525

450

LOAD TRANSIENT

(CIRCUIT OF FIGURE 2)

MAX8576-79 toc07

40μs/div

I

OUT

V

OUT

50mV/div
AC-COUPLED

6A

12A

LOAD TRANSIENT

(CIRCUIT OF FIGURE 3)

MAX8576-79 toc08

40μs/div

I

OUT

V

OUT

50mV/div
AC-COUPLED

5A

2.5A

Typical Operating Characteristics

(TA= +25°C, unless otherwise noted.)

MAX8576–MAX8579

3V to 28V Input, Low-Cost, Hysteretic
Synchronous Step-Down Controllers

6 _______________________________________________________________________________________

Typical Operating Characteristics (continued)

( TA= +25°C, unless otherwise noted.)

POWER-DOWN

(CIRCUIT OF FIGURE 2, MAX8576)

MAX8576-79 toc13

4ms/div

V

IN

V

OUT

I

LX

5V/div

0

1V/div

0

0

10A/div

STARTUP AND SHUTDOWN

(CIRCUIT OF FIGURE 3)

MAX8576-79 toc14

400μs/div

V

EN

V

DL

V

OUT

I

LX

2V/div

0

10V/div

1V/div

0

0

5A/div

0

POWER-DOWN V

CC

(CIRCUIT OF FIGURE 3)

MAX8576-79 toc11

400μs/div

V

IN

V

CC

V

OUT

I

LX

10V/div

0

5V/div

1V/div

5A/div
0

POWER-UP

(CIRCUIT OF FIGURE 2)

MAX8576-79 toc12

1ms/div

V

IN

V

OUT

I

LX

10V/div

0

1V/div

0

0

10A/div

POWER-UP V

IN

(CIRCUIT OF FIGURE 3)

MAX8576-79 toc09

400μs/div

V

IN

V

CC

V

OUT

I

LX

10V/div

0

5V/div

1V/div

5A/div

0

POWER-UP V

CC

(CIRCUIT OF FIGURE 3)

MAX8576-79 toc10

400μs/div

V

IN

V

CC

V

OUT

I

LX

10V/div

0

5V/div

1V/div

5A/div

0