19-2296; 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. This combination makes the MAX1920/MAX1921 excellent highefficiency alternatives to linear regulators in spaceconstrained applications.
Internal synchronous rectification greatly improves efficiency 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.
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
Ordering Information
PART
Applications
TEMP RANGE
PIN-PACKAGE
-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
Next-Generation Wireless Handsets
PDAs, Palmtops, and Handy-Terminals
Battery-Powered Equipment
CDMA Power Amplifier Supply
MAX1920EUT-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
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.
Typical Operating Circuit
TOP VIEW
LX
4.75kΩ
5600pF
CIN
MAX1921
AGND
PGND
4.7µF
IN 1
AGND 2
LX
IN
OUTPUT
1.5V UP TO 400mA
FB
6
4.7µH
AGND
INPUT
2V TO 5.5V
Pin Configuration
5
4
6 LX
MAX1920
MAX1921
5 PGND
MAX1920
ON
4 OUT (FB)
1
SOT23-6
2
3
PGND
SHDN 3
IN
OUT
SHDN
SHDN
OFF
TDFN
( ) ARE FOR MAX1920 ONLY
A "+" sign will replace the first pin indicator on lead-free packages.
________________________________________________________________ Maxim Integrated Products
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.
1
MAX1920/MAX1921
General Description
