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General Description

The MAX1966/MAX1967 are voltage-mode pulse-width-

modulated (PWM), step-down DC-DC controllers that

are ideal for a variety of cost-sensitive applications.

They drive low-cost N-MOSFETs for both the high-side

switch and synchronous rectifier and require no external

Schottky power diode or current-sense resistor. Short-

circuit and current-limit protection is provided by sens-

ing the drain-to-source voltage on the low-side FET.

Both devices can supply outputs as low as 0.8V and are

well suited for DSP cores and other low-voltage logic.

The MAX1966 has an input range of 2.7V to 5.5V while

the MAX1967 has an input range of 2.7V to 28V. In

ultra-low-cost designs, the MAX1966/MAX1967 can

provide efficiency exceeding 90% and can achieve

95% efficiency with optimized component selection.

The MAX1966/MAX1967 operate at 100kHz and ac-

commodate aluminum electrolytic capacitors and pow-

dered-iron core magnetics in minimum-cost designs.

They also provide excellent performance with high-per-

formance surface-mount components. The MAX1966 is

available in a low-cost 8-pin SO package. The MAX1967

is available in a 10-pin µMAX package.

Applications

Features

♦ Cost-Optimized Design

♦ No Schottky Diode or Current-Sense Resistor

Required

♦ >95% Efficiency

♦ Low-Cost External Components

♦ All N-Channel FET Design

♦ 2.7V to 5.5V Input Range (MAX1966)

♦ 2.7V to 28V Input Range (MAX1967)

♦ 0.8V Feedback for Low-Voltage Outputs

♦ 100kHz Switching Frequency Accommodates

Low-Cost Components

♦ Thermal Shutdown

♦ Output Current-Limit and Short-Circuit Protection

MAX1966/MAX1967

Low-Cost Voltage-Mode PWM

Step-Down Controllers

________________________________________________________________ Maxim Integrated Products 1

GND

DLVIN

LXCOMP/EN

BST

TOP VIEW

MAX1966

Pin Configurations

Ordering Information

MAX1966

OUT

2.7V TO

5.5V INPUT

VIN

COMP/EN

GND

BST

Typical Operating Circuit

19-2286; Rev 1; 9/03

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.

Pin Configurations continued at end of data sheet.

Set-Top Boxes

Graphic Card Supplies

xDSL Modems and

Routers

Cable Modems and

Routers

Telecom Power Supplies

Networking Power

Supplies

Termination Supplies

PART TEMP RANGE PIN-PACKAGE

MAX1966ESA -40°C to +85°C 8 SO

MAX1967EUB -40°C to +85°C 10 µMAX

Summary of content (15 pages)

PAGE 1
9-2286; Rev 1; 9/03 Low-Cost Voltage-Mode PWM Step-Down Controllers Applications Set-Top Boxes Graphic Card Supplies xDSL Modems and Routers Cable Modems and Routers Telecom Power Supplies Networking Power Supplies Termination Supplies Features ♦ Cost-Optimized Design ♦ No Schottky Diode or Current-Sense Resistor Required ♦ >95% Efficiency ♦ Low-Cost External Components ♦ All N-Channel FET Design ♦ 2.7V to 5.5V Input Range (MAX1966) ♦ 2.7V to 28V Input Range (MAX1967) ♦ 0.
PAGE 2
MAX1966/MAX1967 Low-Cost Voltage-Mode PWM Step-Down Controllers ABSOLUTE MAXIMUM RATINGS (All Voltages Referenced to GND, Unless Otherwise Noted) VIN to GND (MAX1966)............................................-0.3V to +6V VIN to GND (MAX1967)..........................................-0.3V to +30V VCC to GND (MAX1967)..........-0.3V, lower of 6V or (VIN + 0.3V) FB to GND ................................................................-0.3V to +6V DL, COMP/EN to GND (MAX1966) ................-0.
PAGE 3
Low-Cost Voltage-Mode PWM Step-Down Controllers (VIN = VL = VCC = 5V (MAX1967), VIN = 5V (MAX1966), TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS FB to COMP/EN Transconductance -5µA < ICOMP/EN < 5µA FB Input Bias Current VFB = 0.
PAGE 4
Typical Operating Characteristics (TA = +25°C, unless otherwise noted.) EFFICIENCY vs. LOAD CURRENT (1.8V/3A) MAX1966 VIN = 5.0V 70 90 EFFICIENCY (%) 80 80 VIN = 5.0V 70 60 0.1 1 VIN = 3.3V 70 VIN = 5.0V 60 MAX1966 FIGURE 1 50 50 0.01 VIN = 3.3V 80 MAX1966 FIGURE 1 MAX1966 FIGURE 1 0.01 10 0.1 1 50 10 0.01 0.1 1 10 LOAD CURRENT (A) LOAD CURRENT (A) LOAD CURRENT (A) EFFICIENCY vs. LOAD CURRENT (1.8V/5A) MAX1966 EFFICIENCY vs. LOAD CURRENT (1.2V/3A) MAX1967 EFFICIENCY vs.
PAGE 5
Low-Cost Voltage-Mode PWM Step-Down Controllers EFFICIENCY vs. LOAD CURRENT (3.3V/5A) MAX1967 70 VIN = 24V FREQUENCY vs. TEMPERATURE 120 102 MAX1967 VOUT = 3.3V 100 MAX1966 toc12 MAX1966 toc11 130 FREQUENCY (kHz) VIN = 12V 80 60 110 100 90 MAX1967 FIGURE 2 50 0.01 0.1 1 98 2.5 10 7.0 11.5 16.0 20.5 80 25.0 -40 -25 -10 INPUT VOLTAGE (V) LOAD CURRENT (A) 35 50 65 80 6 4 2 MAX1966 toc14 10 8 SUPPLY CURRENT (mA) 8 20 MAX1967 SUPPLY CURRENT vs.
PAGE 6
Typical Operating Characteristics (continued) (TA = +25°C, unless otherwise noted.) MAX1966 toc18 SHUTDOWN WAVEFORMS MAX1966 toc17 MAX1966/MAX1967 Low-Cost Voltage-Mode PWM Step-Down Controllers NO LOAD 2V/div VIN IOUT VIN = 5.0V VIN = 1.8V L = 22µF VOUT 1V/div INDUCTOR CURRENT 1A/div 10ms/div Pin Description PIN 6 NAME FUNCTION 10 BST Positive Supply of DH Driver. Connect 0.1µF ceramic capacitor between BST and LX. 2 1 COMP/EN Compensation Pin.
PAGE 7
Low-Cost Voltage-Mode PWM Step-Down Controllers The MAX1966/MAX1967 are BiCMOS switch-mode 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 (or a dual MOSFET), an inductor, and input and output filter capacitors. An all N-channel synchronous-rectified design provides high efficiency at reduced cost.
PAGE 8
MAX1966/MAX1967 Low-Cost Voltage-Mode PWM Step-Down Controllers VIN VIN RAMP GENERATOR ERROR COMPARATOR TEMPERATURE SHUTDOWN 5V LINEAR REGULATOR VL ERROR COMPARATOR BST CONTROL LOGIC ERROR AMPLIFIER LX DH COMP/EN CONTROL LOGIC ERROR AMPLIFIER DL FB BST RAMP GENERATOR DH COMP/EN TEMPERATURE SHUTDOWN DL FB GND INTERNAL CHIP SUPPLY VCC 800mV REF SOFT-START -305mV 800mV REF GND SOFT-START -305mV CURRENT-LIMIT COMPARATOR 100kHZ CLOCK GENERATOR CURRENT-LIMIT COMPARATOR 100kHZ
PAGE 9
Low-Cost Voltage-Mode PWM Step-Down Controllers Duty-Factor Limitations for Low VOUT/VVIN Ratios The MAX1966/MAX1967s’ output voltage is adjustable down to 0.8V. However, the minimum duty factor may limit the ability to supply low-voltage outputs from highvoltage inputs. With high-input voltages, the required duty factor is approximately: (VOUT + RDS(ON) ) × ILOAD / VVIN where RDS(ON) x ILOAD is the voltage drop across the synchronous rectifier.
PAGE 10
MAX1966/MAX1967 Low-Cost Voltage-Mode PWM Step-Down Controllers compromise between efficiency and economy. Choose a low-loss inductor having the lowest possible DC resistance. Ferrite-core-type inductors are often the best choice for performance, however; the MAX1966/ MAX1967s’ 100kHz switching rate also allows the use of powdered-iron cores in ultra-low-cost applications where efficiency is not critical.
PAGE 11
Low-Cost Voltage Mode PWM Step-Down Controller 5V TO 28V FOR GATE BIAS VL VIN 3.3V INPUT VCC C6 = L × COUT R3 BST DH VOUT Input Capacitor Selection The input capacitor (C2) reduces noise injection and the current peaks drawn from the input supply. The source impedance to the input supply determines the value of C 2 . High source impedance requires high input capacitance. The input capacitor must meet the ripple current requirement (I RMS ) imposed by the switching currents.
PAGE 12
MAX1966/MAX1967 Low-Cost Voltage-Mode PWM Step-Down Controllers Table 1. Component Selection for Standard Applications VIN = 2.7V TO 5.5V VOUT = 1.8V, 3A MAX1966 (FIGURE 3) DESIGNATION VIN = 2.7V TO 5.5V VOUT = 1.8V, 5A MAX1966 (FIGURE 3) C1 1µF ceramic capacitor 1µF ceramic capacitor C2 Sanyo MV-WX series, 1000µF, 16V, 23mΩ, 1.82A Sanyo MV-WX series, 1000µF, 35V, 18mΩ, 2.77A C3 Sanyo MV-WX series, 1500µF, 6.3V, 23mΩ, 1.82A Sanyo MV-WX series, 1800µF, 16V, 21mΩ, 2.36A C4 0.
PAGE 13
Low-Cost Voltage Mode PWM Step-Down Controller 4) Keep the power traces and load connections short. This practice is essential for high efficiency. Using thick copper PC boards (2oz vs. 1oz) can enhance full-load efficiency by 1% or more. Correctly routing PC board traces is a difficult task that must be approached in terms of fractions of centimeters, where a few milliwatts of excess trace resistance cause a measurable efficiency penalty.
PAGE 14
Chip Information TRANSISTOR COUNT: 3334 PROCESS: BiCMOS 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.) 9LUCSP, 3x3.
PAGE 15
Low-Cost Voltage Mode PWM Step-Down Controller 10LUMAX.EPS e 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 0.114 0.118 H 0.187 0.199 L 0.0157 0.0275 L1 0.037 REF b 0.007 0.0106 e 0.0197 BSC c 0.0035 0.0078 0.0196 REF S α 0∞ 6∞ MAX MIN 1.10 0.15 0.05 0.75 0.95 3.05 2.95 3.00 2.89 3.05 2.95 2.89 3.00 4.75 5.05 0.40 0.70 0.940 REF 0.177 0.270 0.500 BSC 0.