Datasheet

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General Description

The MAX1920/MAX1921 step-down converters deliver

over 400mA to outputs as low as 1.25V. These convert-

ers use a unique proprietary current-limited control

scheme that achieves over 90% efficiency. These

devices maintain extremely low quiescent supply current

(50µA), and their high 1.2MHz (max) operating frequency

permits small, low-cost external components. This combi-

nation makes the MAX1920/MAX1921 excellent high-

efficiency alternatives to linear regulators in space-

constrained applications.

Internal synchronous rectification greatly improves effi-

ciency and eliminates the external Schottky diode

required in conventional step-down converters. Both

devices also include internal digital soft-start to limit

input current upon startup and reduce input capacitor

requirements.

The MAX1920 provides an adjustable output voltage

(1.25V to 4V). The MAX1921 provides factory-preset

output voltages (see the Selector Guide). Both are

available in space-saving 6-pin SOT23 packages. The

MAX1920 is also available in a 6-pin TDFN package.

Applications

Next-Generation Wireless Handsets

PDAs, Palmtops, and Handy-Terminals

Battery-Powered Equipment

CDMA Power Amplifier Supply

Features

♦ 400mA Guaranteed Output Current

♦ Internal Synchronous Rectifier for >90% Efficiency

♦ Tiny 6-Pin SOT23 Package

♦ Available in 6-Pin TDFN Package (MAX1920)

♦ Up to 1.2MHz Switching Frequency for Small

External Components

♦ 50µA Quiescent Supply Current

♦ 0.1µA Logic-Controlled Shutdown

♦ 2V to 5.5V Input Range

♦ Fixed 1.5V, 1.8V, 2.5V, 3V, and 3.3V Output

Voltages (MAX1921)

♦ Adjustable Output Voltage (MAX1920)

♦ ±1.5% Initial Accuracy

♦ Soft-Start Limits Startup Current

Note: The MAX1921 offers five preset output voltage options.

See the Selector Guide, and then insert the proper designator

into the blanks above to complete the part number.

+Denotes lead-free package.

MAX1920/MAX1921

Low-Voltage, 400mA Step-Down

DC-DC Converters in SOT23

________________________________________________________________ Maxim Integrated Products 1

19-2296; Rev 3; 8/05

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.

MAX1921

AGND

SHDN

PGND

OUT

OFF

4.75kΩ

4.7µF

4.7µH

5600pF

OUTPUT

1.5V UP TO 400mA

INPUT

2V TO 5.5V

Typical Operating Circuit

PART

TEMP RANGE

PIN-PACKAGE

MAX1920EUT-T -40°C to +85°C 6 SOT23-6

MAX1920EUT+T -40°C to +85°C 6 SOT23-6

MAX1920ETT-T -40°C to +85°C 6 TDFN

MAX1920ETT+T -40°C to +85°C 6 TDFN

MAX1921EUT_ _-T -40°C to +85°C 6 SOT23-6

MAX1921EUT_ _+T

-40°C to +85°C 6 SOT23-6

Ordering Information

AGND

OUT (FB)SHDN

16LX

5 PGND

PGND

MAX1920

MAX1921

MAX1920

SOT23-6

TOP VIEW

( ) ARE FOR MAX1920 ONLY

A "+" sign will replace the first pin indicator on lead-free packages.

SHDN

123

654

TDFN

Pin Configuration

Summary of content (11 pages)

PAGE 1
9-2296; Rev 3; 8/05 Low-Voltage, 400mA Step-Down DC-DC Converters in SOT23 The MAX1920/MAX1921 step-down converters deliver over 400mA to outputs as low as 1.25V. These converters use a unique proprietary current-limited control scheme that achieves over 90% efficiency. These devices maintain extremely low quiescent supply current (50µA), and their high 1.2MHz (max) operating frequency permits small, low-cost external components.
PAGE 2
MAX1920/MAX1921 Low-Voltage, 400mA Step-Down DC-DC Converters in SOT23 ABSOLUTE MAXIMUM RATINGS IN, FB, SHDN to AGND . . . . . . . . . . . . . . . . . . . . .-0.3V to +6V OUT to AGND, LX to PGND . . . . . . . . . . . .-0.3V to (IN + 0.3V) AGND to PGND . . . . . . . . . . . . . . . . . . . . . . . . . .-0.3V to +0.3V OUT Short Circuit to GND . . . . . . . . . . . . . . . . . . . . . . . . . . .10s Continuous Power Dissipation (TA = +70°C) 6-Pin SOT23-6 (derate 8.7mW/°C above +70°C) . . . .
PAGE 3
Low-Voltage, 400mA Step-Down DC-DC Converters in SOT23 (VIN = 3.6V, SHDN = IN, TA = 0°C to +85°C. Typical parameters are at TA = +25°C, unless otherwise noted.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 350 550 800 mA Ω ILIMN Low-Side Current Limit High-Side On-Resistance RONHS ILX = -40mA, VIN = 3V 0.6 1.1 Rectifier On-Resistance RONSR ILX = 40mA, VIN = 3V 0.5 0.9 Rectifier Off-Current Threshold ILXOFF LX Leakage Current ILXLEAK IN = SHDN = 5.
PAGE 4
Typical Operating Characteristics (continued) (CIN = 2.2µF ceramic, Circuit of Figure 1, components of Table 1, unless otherwise noted.) SWITCHING FREQUENCY vs. LOAD (VOUT = 1.5V) 1000 100 10 1000 100 10 10,000 1 10 100 VOUT = 3.3V 100 VOUT = 1.5V 10 1 1 1 VOUT = 2.5V 1000 VIN = 3.3 VIN = 3.3 0.1 MAX1920 toc09 MAX1920 toc08 10,000 SWITCHING FREQUENCY (kHz) MAX1920 toc07 10,000 NO LOAD SUPPLY CURRENT vs. SUPPLY VOLTAGE NO-LOAD SUPPLY CURRENT (µA) SWITCHING FREQUENCY vs.
PAGE 5
Low-Voltage, 400mA Step-Down DC-DC Converters in SOT23 PIN NAME FUNCTION 1 IN Supply voltage input for MAX1921EUT15 and MAX1921EUT18 is 2V to 5.5V. Supply voltage input for MAX1920 and other voltage versions of MAX1921 is 2.5V to 5.5V. Bypass IN to GND with a 2.2µF ceramic capacitor as close to IN as possible. 6 2 AGND Analog Ground. Connect to PGND. 1 3 SHDN Active-Low Shutdown Input. Connect SHDN to IN for normal operation.
PAGE 6
MAX1920/MAX1921 Low-Voltage, 400mA Step-Down DC-DC Converters in SOT23 Design Procedure The MAX1920/MAX1921 are optimized for small external components and fast transient response. There are several application circuits (Figures 1 through 4) to allow the choice between ceramic or tantalum output capacitor and internally or externally set output voltages.
PAGE 7
Low-Voltage, 400mA Step-Down DC-DC Converters in SOT23 IIN (RMS) = IOUT (MAX) × VOUT (VIN − VOUT ) VIN The output capacitor, COUT, may be either ceramic or tantalum depending upon the chosen application circuit (see Figures 1 through 4). Table 3 lists some suggested capacitor suppliers. Ceramic Output Capacitor For ceramic COUT, use the application circuit of Figure 1 or Figure 2. Calculate the minimum capacitor value as: COUT (MIN) = 2.
PAGE 8
MAX1920/MAX1921 Low-Voltage, 400mA Step-Down DC-DC Converters in SOT23 Table 3. Component Suppliers SUPPLIER Coilcraft PHONE WEBSITE 847-639-6400 www.coilcraft.com Kemet 408-986-0424 www.kemet.com Murata 814-237-1431 www.murata.com Sumida Taiyo Yuden USA 847-956-0666 Japan 81-3-3607-5111 USA Japan USA Toko Japan www.sumida.com 408-573-4150 www.T-Yuden.com 81-3-3833-5441 www.yuden.co.jp 847-297-0070 www.tokoam.com 81-3-3727-1161 www.toko.co.
PAGE 9
Low-Voltage, 400mA Step-Down DC-DC Converters in SOT23 VOUT (V) TOP MARK MAX1920EUT Adjustable ABCO MAX1920ETT Adjustable ADR PART MAX1921EUT33 3.3 ABCJ MAX1921EUT30 3.0 ABCK MAX1921EUT25 2.5 ABCL MAX1921EUT18 1.8 ABCM MAX1921EUT15 1.5 ABCN Chip Information TRANSISTOR COUNT: 1467 Package Information 6, 8, &10L, DFN THIN.EPS (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.
PAGE 10
MAX1920/MAX1921 Low-Voltage, 400mA Step-Down DC-DC Converters in SOT23 Package Information (continued) (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.) COMMON DIMENSIONS MIN. MAX. D 0.70 2.90 0.80 3.10 E A1 2.90 0.00 3.10 0.05 L k 0.20 0.40 0.25 MIN. A2 0.20 REF. SYMBOL A PACKAGE VARIATIONS PKG.
PAGE 11
Low-Voltage, 400mA Step-Down DC-DC Converters in SOT23 6LSOT.EPS PACKAGE OUTLINE, SOT 6L BODY 21-0058 G 1 1 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.