Datasheet

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General Description

The MAX8576–MAX8579 synchronous PWM buck con-

trollers 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 func-

tion 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 V

at 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-cir-

cuit protection. The MAX8576/MAX8578 can start up

into a precharged output without pulling the output volt-

age 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

LXGND

MAX8576

MAX8577

BST

INPUT

UP TO 28V

OUTPUT

0.6V TO 0.9 x V

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

-40°C to +85°C

10 µMAX

MAX8577EUB

-40°C to +85°C

10 µMAX

MAX8578EUB

-40°C to +85°C

10 µMAX

MAX8579EUB

-40°C to +85°C

10 µMAX

Pin Configurations appear at end of data sheet.

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

Summary of content (18 pages)

PAGE 1
9-3289; Rev 1; 6/05 KIT ATION EVALU LE B A IL A AV 3V to 28V Input, Low-Cost, Hysteretic Synchronous Step-Down Controllers 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.
PAGE 2
MAX8576–MAX8579 3V to 28V Input, Low-Cost, Hysteretic Synchronous Step-Down Controllers ABSOLUTE MAXIMUM RATINGS 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 VCC to GND (MAX8578/MAX8579) ..........................-0.3V to +6V SS to GND (MAX8576/MAX8577) ...............-0.3V to (VVL + 0.3)V SS to GND (MAX8578/MAX8579)...............-0.
PAGE 3
V to 28V Input, Low-Cost, Hysteretic Synchronous Step-Down Controllers (VIN = 12V (MAX8576/MAX8577 only), 4.7µF capacitor from VL (MAX8576/MAX8577 only) or VCC (MAX8578/MAX8579 only) to GND; VCC = VEN = 5V (MAX8578/MAX8579 only); 0.01µF capacitor from SS to GND; VFB = 0.65V; VBST = 5V; VLX = VGND = 0V; VOCSET = 11.5V; DH = unconnected; DL = unconnected; TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.
PAGE 4
MAX8576–MAX8579 3V to 28V Input, Low-Cost, Hysteretic Synchronous Step-Down Controllers ELECTRICAL CHARACTERISTICS (continued) (VIN = 12V (MAX8576/MAX8577 only), 4.7µF capacitor from VL (MAX8576/MAX8577 only) or VCC (MAX8578/MAX8579 only) to GND; VCC = VEN = 5V (MAX8578/MAX8579 only); 0.01µF capacitor from SS to GND; VFB = 0.65V; VBST = 5V; VLX = VGND = 0V; VOCSET = 11.5V; DH = unconnected; DL = unconnected; TA = -40°C to +85°C, unless otherwise noted.
PAGE 5
3V to 28V Input, Low-Cost, Hysteretic Synchronous Step-Down Controllers EFFICIENCY vs. LOAD CURRENT (CIRCUIT OF FIGURE 3) EFFICIENCY (%) 60 50 40 60 40 20 20 10 10 1 0.1 10 VOUT = 1.5V 50 30 VIN = 12V VOUT = 1.8V VOUT = 2.5V 70 30 0 1.82 1.81 1.80 1.79 1.78 1.77 1.76 VIN = 12V 1.75 0.1 10 1 5 0 10 15 LOAD CURRENT (A) LOAD CURRENT (A) LOAD CURRENT (A) LINE REGULATION (CIRCUIT OF FIGURE 2) LINE REGULATION (CIRCUIT OF FIGURE 3) SWITCHING FREQUENCY vs.
PAGE 6
MAX8576–MAX8579 3V to 28V Input, Low-Cost, Hysteretic Synchronous Step-Down Controllers Typical Operating Characteristics (continued) ( TA = +25°C, unless otherwise noted.
PAGE 7
3V to 28V Input, Low-Cost, Hysteretic Synchronous Step-Down Controllers STARTUP AND SHUTDOWN (CIRCUIT OF FIGURE 2) MONOTONIC OUTPUT-VOLTAGE RISE (CIRCUIT OF FIGURE 2, MAX8576) MAX8576-79 toc15 MAX8576-79 toc16 10V/div 0 VGS(Q3) 0.5V/div 0 2V/div 0 VSS VOUT VIN 10V/div VOUT 1.5V 0.
PAGE 8
MAX8576–MAX8579 3V to 28V Input, Low-Cost, Hysteretic Synchronous Step-Down Controllers Pin Description PIN MAX8576/ MAX8577 MAX8578/ MAX8579 NAME 1 1 FB Feedback Input. Regulates at VFB = 0.59V. Connect FB to a resistor-divider to set the output voltage. See the Setting the Output Voltage section. 2 2 SS Soft-Start. Use an external capacitor (CSS) to adjust the soft-start time. An internal 80kΩ resistor gives approximately 4ms soft-start time for a 0.01µF external capacitor.
PAGE 9
3V to 28V Input, Low-Cost, Hysteretic Synchronous Step-Down Controllers MAX8576–MAX8579 BST FAULT OCSET LX MAX8578/ MAX8579 EN GND 0.3 DHI DH FB DRIVERS OVP LOGIC 0.75V SS SS RAMP LX DLI DL 0.05V IN MAX8576 MAX8577 VL REG VLOK POK MAX8576–MAX8579 VL VCC MAX8578 MAX8579 REF REFOK GND Figure 1.
PAGE 10
MAX8576–MAX8579 3V to 28V Input, Low-Cost, Hysteretic Synchronous Step-Down Controllers INPUT 9V TO 24V C1 C11 C2 R1 1 FB OCSET 10 2 SS IN R2 C4 C3 9 C8 C12 C5 OFF ON R4 3 Q3 MAX8576 MAX8577 VL C6 DH Q1 8 R7 R3 OUTPUT 1.8V/12A L1 R5 4 GND 5 DL LX 7 BST 6 C7 C9 C13 Q2 R6 R8 D1 12V INPUT, 1.8V/12A OUTPUT (fS = 300kHz) CIRCUIT IS TARGETED FOR 10.8V TO 13.2V INPUT. HOWEVER, INPUT RANGE OF 9V TO 24V IS POSSIBLE FOR IC EVALUATION.
PAGE 11
3V to 28V Input, Low-Cost, Hysteretic Synchronous Step-Down Controllers COMPONENTS QTY C1, C2 2 DESCRIPTION/VENDOR PART NUMBER MAX8578/MAX8579 External Component List DESCRIPTION/VENDOR PART NUMBER COMPONENT QTY 470µF, 35V aluminum electrolytic capacitors Sanyo 35MV470WX C14 1 10µF, 25V X5R ceramic capacitor C15 1 1µF, 25V X5R ceramic capacitor C16 1 4700pF, 10V X7R ceramic capacitor C3 1 10µF, 25V X7R ceramic capacitor C17 1 4.7µF, 6.3V X5R ceramic capacitor C4 1 0.
PAGE 12
MAX8576–MAX8579 3V to 28V Input, Low-Cost, Hysteretic Synchronous Step-Down Controllers 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). The MAX8578/MAX8579 have a logic-enable input to turn on and off the output.
PAGE 13
3V to 28V Input, Low-Cost, Hysteretic Synchronous Step-Down Controllers Synchronous-Rectifier Driver (DL) Synchronous rectification reduces conduction losses in the rectifier by replacing the normal Schottky catch diode with a low-resistance MOSFET switch. The MAX8576–MAX8579 also use the synchronous rectifier to ensure proper startup of the boost gate-driver circuit.
PAGE 14
MAX8576–MAX8579 3V to 28V Input, Low-Cost, Hysteretic Synchronous Step-Down Controllers ⎛ VOUT + 0.01V + (RDC × 0.5 × IOUTMAX ) ⎞ R3 = R1 × ⎜ − 1⎟ VFB ⎝ ⎠ where VFB = 0.590V, RDC is the DC resistance of the output inductor, IOUTMAX is the maximum output current. The term 0.01V is to reflect 1/2 of the feedbackthreshold hysteresis. Inductor Value The inductor value is bounded by two operating parameters: the switching frequency and the inductor peakto-peak ripple current.
PAGE 15
3V to 28V Input, Low-Cost, Hysteretic Synchronous Step-Down Controllers ⎛V ⎞ PN1CC = ⎜ OUT ⎟ × ILOAD2 × RDS(ON) ⎝ VIN ⎠ Input Capacitor The input filter capacitor reduces peak currents drawn from the power source and reduces noise and voltage ripple on the input caused by the circuit’s switching. The input capacitor must meet the ripple-current requirement (IRMS) imposed by the switching currents defined by the following equation: IRMS = ILOAD × VOUT × (VIN − VOUT ) VIN Use RDS(ON) at TJ(MAX).
PAGE 16
MAX8576–MAX8579 3V to 28V Input, Low-Cost, Hysteretic Synchronous Step-Down Controllers chosen based on a prototype or evaluation circuit. As a general rule, a smaller current ripple results in less output voltage ripple. Since the inductor ripple current is a factor of the inductor value and input voltage, the output voltage ripple decreases with larger inductance and increases with higher input voltages.
PAGE 17
3V to 28V Input, Low-Cost, Hysteretic Synchronous Step-Down Controllers 5) Place the MOSFET as close as possible to the IC to minimize trace inductance. If parallel MOSFETs are used, keep the gate connection to both gates equal. 6) Connect the drain leads of the power MOSFET to a large copper area to help cool the device. Refer to the power MOSFET data sheet for the recommended copper area. 2) For output current > 10A, a four-layer PC board is recommended.
PAGE 18
Package Information (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.) e 10LUMAX.EPS MAX8576–MAX8579 3V to 28V Input, Low-Cost, Hysteretic Synchronous Step-Down Controllers 4X S 10 10 H Ø0.50±0.1 0.6±0.1 1 1 0.6±0.1 BOTTOM VIEW TOP VIEW D2 MILLIMETERS INCHES MAX DIM MIN 0.043 A 0.006 0.002 A1 A2 0.030 0.037 0.120 0.116 D1 0.118 D2 0.114 0.120 E1 0.116 0.118 E2 0.114 0.