Instruction Manual

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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 alu-

minum electrolytic capacitors. Input undervoltage lock-

out prevents proper operation under power-sag

operations to prevent external MOSFETs from overheat-

ing. Internal soft-start is included to reduce inrush cur-

rent. 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 0; 7/03

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.

PART TEMP RANGE PIN-PACKAGE

MAX8545EUB -40°C to +85°C 10 µMAX

MAX8546EUB -40°C to +85°C 10 µMAX

MAX8548EUB -40°C to +85°C 10 µMAX

Selector Guide

PART

SWITCHING

FREQUENCY

CURRENT-LIMIT

THRESHOLD

MAX8545 300kHz -320mV

MAX8546 300kHz -165mV

MAX8548 100kHz -320mV

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

Summary of content (18 pages)

PAGE 1
9-2795; Rev 0; 7/03 Low-Cost, Wide Input Range, Step-Down Controllers with Foldback Current Limit Features ♦ 2.7V to 28V Input Range ♦ Foldback Short-Circuit Protection ♦ No Additional Bias Supply Needed ♦ 0.8V to 0.
PAGE 2
MAX8545/MAX8546/MAX8548 Low-Cost, Wide Input Range, Step-Down Controllers with Foldback Current Limit ABSOLUTE MAXIMUM RATINGS LX to GND ......................................................................0 to 30V Input Current (any pin) .....................................................±50mA Continuous Power Dissipation (TA = +70°C) 10-Pin µMAX (derate 5.6mW/°C above +70°C) ..........444mW Operating Temperature Range ...........................-40°C to +85°C Junction Temperature .....................
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 UNITS ERROR AMPLIFIER FB Regulation Voltage 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 60 50 40 30 30 20 20 VIN = 3.3V VOUT = 1.2V 0.1 0.01 1 0 10 VOUT = 1.8V 60 50 40 80 VOUT = 1.8V 70 60 VOUT = 1.2V 50 90 40 10 40 0.1 0.01 10 1 1 10 EFFICIENCY vs. LOAD CURRENT (CIRCUIT OF FIGURE 2; TABLE 2b) (CIRCUIT OF FIGURE 2; TABLE 2b) CHANGE IN OUTPUT VOLTAGE vs. LOAD CURRENT VOUT = 1.8V 60 50 VOUT = 1.
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 = 6V OUTPUT VOLTAGE (V) ILOAD = 6V 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 2.48 1.78 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 Compensation Input. Pull COMP/EN low with an open-collector or open-drain device to turn off the output. 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.
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 The DC gain of the power modulator is: 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 PC board 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.
PAGE 17
Low-Cost, Wide Input Range, Step-Down Controllers with Foldback Current Limit TOP VIEW COMP/EN 1 FB 2 10 BST 9 DH 8 LX VIN 4 7 GND VL 5 6 DL VCC Chip Information TRANSISTOR COUNT: 3351 PROCESS: BiCMOS 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 ÿ 0.50±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 D1 0.116 0.120 0.114 0.118 D2 0.116 E1 0.120 E2 0.