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General Description

The MAX8545/MAX8546/MAX8548 are voltage-mode

pulse-width-modulated (PWM), step-down DC-DC con-

trollers ideal for a variety of cost-sensitive applications.

They drive low-cost n-channel MOSFETs for both the

high-side switch and synchronous rectifier, and require

no external current-sense resistor. These devices can

supply output voltages as low as 0.8V.

The MAX8545/MAX8546/MAX8548 have a wide 2.7V to

28V input range, and do not need any additional bias

voltage. The output voltage can be precisely regulated

from 0.8V to 0.83 x V

. These devices can provide effi-

ciency up to 95%. Lossless short-circuit and current-limit

protection is provided by monitoring the R

DS(ON)

of the

low-side MOSFET. The MAX8545 and MAX8548 have a

current-limit threshold of 320mV, while the MAX8546 has

a current-limit threshold of 165mV. All devices feature

foldback-current capability to minimize power dissipation

under short-circuit condition. Pulling the COMP/EN pin

low with an open-collector or low-capacitance, open-

drain device can shut down all devices.

The MAX8545/MAX8546 operate at 300kHz and the

MAX8548 operates at 100kHz. The MAX8545/MAX8546/

MAX8548 are compatible with low-cost aluminum elec-

trolytic capacitors. Input undervoltage lockout prevents

proper operation under power-sag operations to prevent

external MOSFETs from overheating. Internal soft-start is

included to reduce inrush current. These devices are

offered in space-saving 10-pin µMAX

packages.

Applications

Features

♦ 2.7V to 28V Input Range

♦ Foldback Short-Circuit Protection

♦ No Additional Bias Supply Needed

♦ 0.8V to 0.83 x V

Output

♦ Up to 95% Efficiency

♦ Low-Cost External Components

♦ No Current-Sense Resistor

♦ All n-Channel MOSFET Design

♦ Adaptive Gate Drivers Eliminate Shoot-Through

♦ Lossless Overcurrent and Short-Circuit

Protection

♦ 300kHz Switching Frequency

(MAX8545/MAX8546)

♦ 100kHz Switching Frequency (MAX8548)

♦ Pin-Compatible with the MAX1967

♦ Thermal Shutdown

MAX8545/MAX8546/MAX8548

Low-Cost, Wide Input Range, Step-Down

Controllers with Foldback Current Limit

________________________________________________________________ Maxim Integrated Products 1

MAX8545

MAX8546

MAX8548

OFF

OPTIONAL

BSTV

COMP/

VLV

GND

INPUT

2.7V TO 28V

OUTPUT

0.8V TO

0.9 x V

UP TO 6A

Typical Operating Circuit

Ordering Information

Pin Configuration appears at end of data sheet.

19-2795; Rev 2; 6/07

For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,

or visit Maxim’s website at www.maxim-ic.com.

PART

TEMP RANGE

PIN-

PACKAGE

PKG

CODE

MAX8545EUB

-40°C to +85°C

10 µMAX

U10-2

MAX8545EUB+

-40°C to +85°C

10 µMAX

U10-2

MAX8546EUB

-40°C to +85°C

10 µMAX

U10-2

MAX8546EUB+

-40°C to +85°C

10 µMAX

U10-2

MAX8548EUB

-40°C to +85°C

10 µMAX

U10-2

MAX8548EUB+

-40°C to +85°C

10 µMAX

U10-2

Selector Guide

PART

SWITCHING

FREQUENCY

(kHz)

CURRENT-LIMIT

THRESHOLD

(mV)

MAX8545 300 -320

MAX8546 300 -165

MAX8548 100 -320

Set-Top Boxes

Graphic Card and Video

Supplies

Desktops and Desknotes

PCI Express Power

Supplies

Telecom Power Supplies

Notebook Docking

Station Supplies

Cable Modems and

Routers

Networking Power

Supplies

+Denotes a lead-free package.

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

Summary of content (18 pages)

PAGE 1
9-2795; Rev 2; 6/07 Low-Cost, Wide Input Range, Step-Down Controllers with Foldback Current Limit The MAX8545/MAX8546/MAX8548 are voltage-mode pulse-width-modulated (PWM), step-down DC-DC controllers ideal for a variety of cost-sensitive applications. They drive low-cost n-channel MOSFETs for both the high-side switch and synchronous rectifier, and require no external current-sense resistor. These devices can supply output voltages as low as 0.8V. The MAX8545/MAX8546/MAX8548 have a wide 2.
PAGE 2
MAX8545/MAX8546/MAX8548 Low-Cost, Wide Input Range, Step-Down Controllers with Foldback Current Limit ABSOLUTE MAXIMUM RATINGS (All voltages referenced to GND unless otherwise noted.) VIN to GND ............................................................-0.3V to +30V VCC to GND .............................-0.3V, lower of 6V or (VL + 0.3V) FB to GND ................................................................-0.3V to +6V BST to GND ............................................................-0.
PAGE 3
Low-Cost, Wide Input Range, Step-Down Controllers with Foldback Current Limit MAX8545/MAX8546/MAX8548 ELECTRICAL CHARACTERISTICS (continued) (VIN = VL = VCC = 5V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX 2.7V < VCC < 5.5V, 0°C to +85°C 0.787 0.800 0.815 2.7V < VCC < 5.5V, -40°C to +85°C 0.782 0.800 0.
PAGE 4
Typical Operating Characteristics (VIN = VL = VCC = 5V, typical values are at TA = +25°C, unless otherwise noted.) EFFICIENCY vs. LOAD CURRENT 50 40 30 VOUT = 1.8V 70 60 50 40 0.1 0 10 1 0.01 10 1 0.01 VOUT = 1.8V 90 80 EFFICIENCY (%) VOUT = 3.3V 60 50 40 VOUT = 1.8V 70 60 VOUT = 1.2V 50 40 0.1 1 10 40 10 1 EFFICIENCY vs. LOAD CURRENT EFFICIENCY vs. LOAD CURRENT CHANGE IN OUTPUT VOLTAGE vs. LOAD CURRENT 50 80 VOUT = 1.2V 40 50 20 20 1 LOAD CURRENT (A) 2.510 2.505 2.
PAGE 5
Low-Cost, Wide Input Range, Step-Down Controllers with Foldback Current Limit CHANGE IN OUTPUT VOLTAGE vs. INPUT VOLTAGE CHANGE IN OUTPUT VOLTAGE vs. INPUT VOLTAGE MAX8545/46/48 toc11 1.83 ILOAD = 6A OUTPUT VOLTAGE (V) ILOAD = 6A OUTPUT VOLTAGE (V) 2.52 MAX8545/46/48 toc10 1.84 1.82 1.81 1.80 2.51 2.50 2.49 1.79 1.78 2.48 3.0 3.5 4.0 4.5 10 12 14 INPUT VOLTAGE (V) FREQUENCY vs. INPUT VOLTAGE 20 22 24 MAX8545/46/48 toc12 VOUT = 2.
PAGE 6
Typical Operating Characteristics (continued) (VIN = VL = VCC = 5V, typical values are at TA = +25°C, unless otherwise noted.
PAGE 7
Low-Cost, Wide Input Range, Step-Down Controllers with Foldback Current Limit PIN NAME FUNCTION 1 COMP/EN 2 FB 3 VCC Internal Chip Supply. Connect VCC to VL through a 10Ω resistor. Bypass VCC to GND with at least a 0.1µF ceramic capacitor. 4 VIN Power Supply for LDO Regulator for VIN > 5.5V, and Chip Supply for VIN < 5.5V. Bypass VIN with at least a 1µF ceramic capacitor to GND. 5 VL Output of Internal 5V LDO. Connect VL to VIN for VIN < 5.5V.
PAGE 8
MAX8545/MAX8546/MAX8548 Low-Cost, Wide Input Range, Step-Down Controllers with Foldback Current Limit Detailed Description The MAX8545/MAX8546/MAX8548 are BiCMOS switchmode power-supply controllers designed to implement simple, buck-topology regulators in cost-sensitive applications. The main power-switching circuit consists of two n-channel MOSFETs, an inductor, and input/output filter capacitors. An all n-channel synchronous-rectified design provides high efficiency at reduced cost.
PAGE 9
Low-Cost, Wide Input Range, Step-Down Controllers with Foldback Current Limit VOUT + (RDS(ON) × ILOAD ) VIN Setting the Output Voltage An output voltage between 0.8V and (0.83 x VIN) can be configured by connecting FB to a resistive divider between the output and GND (see Figures 1 and 2). Select resistor R4 in the 1kΩ to 10kΩ range. R3 is then given by: where RDS(ON) x ILOAD is the voltage drop across the synchronous rectifier.
PAGE 10
MAX8545/MAX8546/MAX8548 Low-Cost, Wide Input Range, Step-Down Controllers with Foldback Current Limit +2.7V TO +5.5V INPUT C4 C3 C2 C1 R1 VIN D1 VL VCC C9 C5 MAX8545* MAX8546 MAX8548* OUT 1.8V/3A OR 6A L1 LX C6 DL COMP/ EN D2 Q1 BST DH C7 C8 GND R2 R3 C10 FB C11 R4 *FOLLOW THE DATA SHEET DESIGN PROCEDURE TO SELECT THE EXTERNAL COMPONENTS FOR THE MAX8545/MAX8548. Figure 1. Typical Application Circuit (2.
PAGE 11
Low-Cost, Wide Input Range, Step-Down Controllers with Foldback Current Limit Power MOSFET Selection The MAX8545/MAX8546/MAX8548 drive two external, logic-level, n-channel MOSFETs as the circuit switching elements. The key selection parameters are: 1) On-resistance (RDS(ON)): the lower, the better. 2) Maximum drain-to-source voltage (VDSS) should be at least 10% higher than the input supply rail at the high-side MOSFET’s drain. 3) Gate charges (QG, QGD, QGS): the lower, the better.
PAGE 12
MAX8545/MAX8546/MAX8548 Low-Cost, Wide Input Range, Step-Down Controllers with Foldback Current Limit with DH and DL to slow down the switching transitions. However, adding series resistors increases the power dissipation of the MOSFET, so ensure temperature ratings of the MOSFET are not exceeded. Input-Capacitor Selection The input capacitors (C2 and C3 in Figure 1) reduce noise injection and current peaks drawn from the input supply.
PAGE 13
Low-Cost, Wide Input Range, Step-Down Controllers with Foldback Current Limit GMOD(DC) = VIN VRAMP where VRAMP = 1V. The pole frequency due to the inductor and output capacitor is: fPMOD = 1 2π LCOUT The zero frequency due to the output capacitor’s ESR is: 1 fZESR = 2π × ESR × COUT The output capacitor is usually comprised of several same capacitors connected in parallel.
PAGE 14
MAX8545/MAX8546/MAX8548 Low-Cost, Wide Input Range, Step-Down Controllers with Foldback Current Limit VIN DH RAMP GENERATOR N VOUT L PWM LX DL COUT N R3 FB COMP/EN R4 ERROR AMPLIFIER R2 C10 MAX8545 MAX8546 MAX8548 0.8V Figure 3. Compensation Scheme ground terminals flush against one another. Follow these guidelines for good PCB layout: 1) Keep the high-current paths short, especially at the ground terminals. This practice is essential for stable, jitter-free operation.
PAGE 15
Low-Cost, Wide Input Range, Step-Down Controllers with Foldback Current Limit COMPONENT QTY DESCRIPTION C1, C4 2 1µF, 10V X7R ceramic capacitors Taiyo Yuden LMK212BJ105MG C2 0 Not installed 1 1200µF, 10V, 44mΩ, 1.25A aluminum electrolytic capacitor SANYO 10MV1200AX (10 x 16 case size) 3 0.1µF, 10V X7R ceramic capacitors Kemet C0603C104M8RAC 2 1000µF, 6.3V, 69mΩ, 0.8A aluminum electrolytic capacitors SANYO 6.3MV1000AX (8 x 20 case size) C10 1 1.
PAGE 16
MAX8545/MAX8546/MAX8548 Low-Cost, Wide Input Range, Step-Down Controllers with Foldback Current Limit Table 2a. Component Selection for Standard Applications for VIN = 10V to 24V, VOUT = 2.5V / 3A (Figure 2) (MAX8546 Only) COMPONENT QTY C1 1 1µF, 10V X7R ceramic capacitor Taiyo Yuden LMK212BJ105MG C2 0 Not installed 1 470µF, 35V, 39mΩ, 1.45A aluminum electrolytic capacitor SANYO 35MV470AX (10 x 22 case size) C3 2 1µF, 35V X7R ceramic capacitors Taiyo Yuden GMK316BJ105ML 3 0.
PAGE 17
Low-Cost, Wide Input Range, Step-Down Controllers with Foldback Current Limit TRANSISTOR COUNT: 3351 PROCESS: BiCMOS TOP VIEW COMP/EN 1 FB 10 BST 9 DH 8 LX VIN 4 7 GND VL 5 6 DL VCC Chip Information 2 3 MAX8545 MAX8546 MAX8548 μMAX ______________________________________________________________________________________ 17 MAX8545/MAX8546/MAX8548 Pin Configuration
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 MAX8545/MAX8546/MAX8548 Low-Cost, Wide Input Range, Step-Down Controllers with Foldback Current Limit 4X S 10 10 INCHES H Ø0.50±0.1 0.6±0.1 1 1 0.6±0.1 BOTTOM VIEW TOP VIEW D2 MILLIMETERS MAX DIM MIN 0.043 A 0.006 A1 0.002 A2 0.030 0.037 0.120 D1 0.116 0.118 0.114 D2 0.116 0.120 E1 0.