Datasheet

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MAX1830/MAX1831

3A, 1MHz, Low-Voltage, Step-Down Regulators with

Synchronous Rectification and Internal Switches

________________________________________________________________ Maxim Integrated Products 1

19-2198; Rev 0; 10/01

General Description

The MAX1830/MAX1831 constant-off-time, pulse-width-

modulated (PWM) step-down DC-DC converters are

ideal for use in 5V and 3.3V to low-voltage conversion

necessary in notebook and subnotebook computers.

These devices feature internal synchronous rectification

for high efficiency and reduced component count. They

require no external Schottky diode. The internal 45mΩ

PMOS power switch and 55mΩ NMOS synchronous-rec-

tifier switch easily deliver continuous load currents up to

3A. The MAX1830 produces preset +2.5V, +1.8V, or

+1.5V output voltage or an adjustable output from +1.1V

to V

. The MAX1831 produces preset +3.3V, +2.5V, and

+1.5V output voltages and an adjustable output from

+1.1V to V

IN.

They achieve efficiencies as high as 94%.

The MAX1830/MAX1831 use a unique current-mode,

constant-off-time, PWM control scheme, which includes

Idle Mode™ to maintain high efficiency during light-

load operation. The programmable constant-off-time

architecture sets switching frequencies up to 1MHz,

allowing the user to optimize performance trade-

offs between efficiency, output switching noise, compo-

nent size, and cost. Both devices are designed for con-

tinuous output currents up to 3A, an internal digital

soft-start to limit surge currents during startup, a 100%

duty cycle mode for low-dropout operation, and a

low-power shutdown mode that disconnects the input

from the output and reduces supply current below

1µA.The MAX1830/MAX1831 are available in 16-pin

QSOP packages.

For similar devices that provide continuous output

currents of 1A to 3A, refer to the MAX1644, MAX1623,

and MAX1742/MAX1842/MAX1843 data sheets.

Applications

5V or 3.3V to Low-Voltage Conversion

CPU I/O Supplies

Chipset Supplies

Notebook and Subnotebook Computers

Features

♦ ±1.5% Output Accuracy

♦ 94% Efficiency

♦ Internal PMOS/NMOS Switches

45mΩ/55mΩ On-Resistance at V

= +4.5V

50mΩ/55mΩ On-Resistance at V

= +3V

♦ Output Voltages

+3.3V, +2.5V, or +1.5V Pin Selectable (MAX1831)

+2.5V, +1.8V, or +1.5V Pin Selectable (MAX1830)

+1.1V to V

Adjustable (Both Devices)

♦ +3V to +5.5V Input Voltage Range

♦ 750µA (max) Operating Supply Current

♦ <1µA Shutdown Supply Current

♦ Programmable Constant-Off-Time Operation

♦ Up to 1MHz Switching Frequency

♦ Idle Mode Operation at Light Loads

♦ Thermal Shutdown

♦ Internal Digital Soft-Start Inrush Current Limiting

♦ 100% Duty Cycle During Low-Dropout Operation

♦ Output Short-Circuit Protection

♦ 16-Pin QSOP Package

Idle Mode is a trademark of Maxim Integrated Products, Inc.

Typical Configuration

TOFF

COMP

FBSEL

SHDN

PGND

GND

REF

MAX1830

MAX1831

OUTPUT

+1.1V TO

INPUT

+3V TO

+5.5V

EVALUATION KIT

AVAILABLE

Pin Configuration appears at end of data sheet.

PART

MAX1830EEE

-40°C to +85°C

TEMP. RANGE PIN-PACKAGE

16 QSOP

Ordering Information

MAX1831EEE

-40°C to +85°C 16 QSOP

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.

Summary of content (13 pages)

PAGE 1
9-2198; Rev 0; 10/01 KIT EVALUATION AVAILABLE 3A, 1MHz, Low-Voltage, Step-Down Regulators with Synchronous Rectification and Internal Switches Applications Features ♦ ±1.5% Output Accuracy ♦ 94% Efficiency ♦ Internal PMOS/NMOS Switches 45mΩ/55mΩ On-Resistance at VIN = +4.5V 50mΩ/55mΩ On-Resistance at VIN = +3V ♦ Output Voltages +3.3V, +2.5V, or +1.5V Pin Selectable (MAX1831) +2.5V, +1.8V, or +1.5V Pin Selectable (MAX1830) +1.1V to VIN Adjustable (Both Devices) ♦ +3V to +5.
PAGE 2
MAX1830/MAX1831 3A, 1MHz, Low-Voltage, Step-Down Regulators with Synchronous Rectification and Internal Switches ABSOLUTE MAXIMUM RATINGS VCC, IN, SHDN to GND ............................................-0.3V to +6V IN to VCC .............................................................................±0.3V GND to PGND.....................................................................±0.3V COMP, FB, TOFF, FBSEL, REF to GND .....-0.3V to (VCC + 0.3V) LX Current (Note 1) ...................................
PAGE 3
A, 1MHz, Low-Voltage, Step-Down Regulators with Synchronous Rectification and Internal Switches (VIN = VCC = +3.3V, FBSEL = GND, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL Shutdown Supply Current TYP MAX SHDN = GND, into VCC and IN pins; LX = 0 or 3.3V CONDITIONS MIN 0.2 20 SHDN = GND, into IN with LX = 0 0.2 20 20 SHDN = GND, into IN with LX = 3.3V 0.
PAGE 4
ELECTRICAL CHARACTERISTICS (continued) (VIN = VCC = +3.3V, FBSEL = GND, TA = -40°C to +85°C, unless otherwise noted.) (Note 5) PARAMETER SYMBOL CONDITIONS MIN VCC = VIN = +3V to +5.5V, ILOAD = 0, FBSEL = GND Adjustable Output Voltage Range TYP MAX UNITS VREF VIN V Reference Voltage VREF 1.078 1.122 V Current-Limit Threshold ILIMIT 3.9 5.4 A Idle Mode Current Threshold IIM 0.14 1.0 A PMOS Switch On-Resistance RON, P ILX = 0.5A NMOS Switch On-Resistance RON, N ILX = 0.
PAGE 5
3A, 1MHz, Low-Voltage, Step-Down Regulators with Synchronous Rectification and Internal Switches SWITCHING FREQUENCY vs. OUTPUT CURRENT NORMALIZED OUTPUT ERROR vs. OUTPUT CURRENT 0 -0.05 -0.10 -0.15 VIN = 3.3V VOUT = 1.5V L = 1.5µH VIN = 5.0V VOUT = 1.5V L = 1.5µH VIN = 5.0V, VOUT = 1.5V, L = 1.5µH 1000 IIN 1A/div 800 VSHDN 5V/div 600 VIN = 3.3V, VOUT = 1.5V, L = 1.5µH 400 VOUT 1V/div 200 -0.20 -0.25 0.001 MAX1830 toc05 MAX1830 toc04 0.
PAGE 6
3A, 1MHz, Low-Voltage, Step-Down Regulators with Synchronous Rectification and Internal Switches MAX1830/MAX1831 Pin Description PIN NAME FUNCTION 1, 3, 14, 16 LX Connection for the drains of the PMOS power switch and NMOS synchronous-rectifier switch. Connect the inductor from this node to the output filter capacitor and load. 2, 4 IN Supply Voltage Input for the internal PMOS power switch 5 SHDN Shutdown Control Input.
PAGE 7
3A, 1MHz, Low-Voltage, Step-Down Regulators with Synchronous Rectification and Internal Switches IN CIN 22µF, 6.3V X5R 10Ω 2.2µF LX MAX1830 FB MAX1831 VCC PGND 470pF SHDN COMP MAX1830/MAX1831 L 1.5µF INPUT OUTPUT SUMIDA CDRH-6D28 COUT 120µF, 4V Panasonic SP GND FBSEL REF 1µF TOFF MAX1830 VOUT = 2.5V, FBSEL = VOUT = 1.8V, FBSEL = VOUT = 1.5V, FBSEL = VCC REF FLOATING MAX1831 VOUT = 2.5V, FBSEL = VOUT = 3.3V, FBSEL = VOUT = 1.5V, FBSEL = VCC REF FLOATING RTOFF Figure 1.
PAGE 8
Table 1. Recommended Component Values (IOUT = 3.0A) VIN (V) VOUT (V) fPWM (kHz) L (µH) RTOFF (kΩ) 5 3.3 800 2.2 39 5 2.5 865 2.2 56 5 1.8 850 2.2 75 5 1.5 860 2.2 82 5 1.1 625 2.2 130 3.3 2.5 570 1.5 39 3.3 1.8 850 1.5 51 3.3 1.5 860 1.5 62 3.3 1.1 680 1.5 100 100% Duty-Cycle Operation When the input voltage drops near the output voltage, the duty cycle increases until the PMOS MOSFET is on continuously.
PAGE 9
3A, 1MHz, Low-Voltage, Step-Down Regulators with Synchronous Rectification and Internal Switches PIN OUTPUT VOLTAGE (V) FBSEL FB MAX1830 MAX1831 VCC Output voltage 2.5 2.5 Unconnected Output voltage 1.5 1.5 REF Output voltage 1.8 3.3 GND Resistive divider Adjustable VOUT LX MAX1830 MAX1831 R2 FB R1 R1 = 30kΩ R2 = R1(VOUT / VREF - 1) VREF = 1.1V Figure 4.
PAGE 10
MAX1830/MAX1831 3A, 1MHz, Low-Voltage, Step-Down Regulators with Synchronous Rectification and Internal Switches voltage and ground (Figure 4). Regulation is maintained for adjustable output voltages when VFB = VREF. Use 30kΩ for R1. R2 is given by the equation: V  R2 = R1  OUT − 1  VREF  where VREF is typically 1.1V.
PAGE 11
3A, 1MHz, Low-Voltage, Step-Down Regulators with Synchronous Rectification and Internal Switches MAX1830/MAX1831 MAX1830/MAX1831 MAXIMUM RECOMMENDED CONTINUOUS OUTPUT CURRENT vs. TEMPERATURE MAXIMUM RECOMMENDED BURST CURRENT vs. BURST CURRENT DUTY CYCLE 3.50 3.40 3.40 3.20 BURST CURRENT (A) OUTPUT CURRENT (A) 3.30 3.10 3.00 2.90 2.80 TA = +55°C 3.20 TA = +85°C 3.00 2.80 2.70 2.60 2.60 2.50 IOUT IS A 100Hz SQUARE WAVE FROM 1A TO THE BURST CURRENT 0.7IN2 OF 1-OZ COPPER 2.40 2.
PAGE 12
MAX1830/MAX1831 3A, 1MHz, Low-Voltage, Step-Down Regulators with Synchronous Rectification and Internal Switches The following points are in order of decreasing importance: 1) Minimize switched-current and high-current ground loops. Connect the input capacitor’s ground, the output capacitor’s ground, and PGND. Connect the resulting island to GND at only one point. 2) Connect the input filter capacitor less than 5mm away from IN.
PAGE 13
3A, 1MHz, Low-Voltage, Step-Down Regulators with Synchronous Rectification and Internal Switches QSOP.EPS Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.