19-2224; Rev 3; 12/03
500kHz Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
General Description
The MAX1901/MAX1902/MAX1904 are buck-topology,
step-down, switch-mode, power-supply controllers that
generate logic-supply voltages in battery-powered sys-
tems. These high-performance, dual/triple-output devices
include on-board power-up sequencing, power-good sig-
naling with delay, digital soft-start, secondary winding
control, low dropout circuitry, internal frequency-compen-
sation networks, and automatic bootstrapping.
Up to 97% efficiency is achieved through synchronous
rectification and Maxim’s proprietary Idle Mode™ control
scheme. Efficiency is greater than 80% over a 1000:1
load-current range, which extends battery life in system
suspend or standby mode. Excellent dynamic response
corrects output load transients within five clock cycles.
Strong 1A on-board gate drivers ensure fast external N-
channel MOSFET switching.
These devices feature a logic-controlled and synchroniz-
able, fixed-frequency, pulse-width modulation (PWM)
operating mode. This reduces noise and RF interference
in sensitive mobile communications and pen-entry appli-
cations. Asserting the
SKIP
pin enables fixed-frequency
mode, for lowest noise under all load conditions.
The MAX1901/MAX1902/MAX1904 include two PWM reg-
ulators, adjustable from 2.5V to 5.5V with fixed 5.0V and
3.3V modes. All these devices include secondary feed-
back regulation, and the MAX1902 contains a 12V/120mA
linear regulator. The MAX1901/MAX1904 include a sec-
ondary feedback input (SECFB), plus a control pin
(STEER) that selects which PWM (3.3V or 5V) receives the
secondary feedback signal. SECFB provides a method
for adjusting the secondary winding voltage regulation
point with an external resistor divider, and is intended to
aid in creating auxiliary voltages other than fixed 12V.
The MAX1901/MAX1902 contain internal output overvolt-
age and undervoltage protection features.
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Features
97% Efficiency
4.2V to 30V Input Range
2.5V to 5.5V Dual Adjustable Outputs
Selectable 3.3V and 5V Fixed or Adjustable
Outputs (Dual Mode™)
12V Linear Regulator
Adjustable Secondary Feedback
(MAX1901/MAX1904)
5V/50mA Linear Regulator Output
Precision 2.5V Reference Output
Programmable Power-Up Sequencing
Power-Good (RESET) Output
Output Overvoltage Protection
(MAX1901/MAX1902)
Output Undervoltage Shutdown
(MAX1901/MAX1902)
333kHz/500kHz Low-Noise, Fixed-Frequency
Operation
Low-Dropout, 98% Duty-Factor Operation
2.5mW Typical Quiescent Power (12V input, both
SMPSs on)
4µA Typical Shutdown Current
MAX1901/MAX1902/MAX1904
Ordering Information
PART
MAX1901EAI
MAX1901ETJ
MAX1902EAI
MAX1902ETJ
MAX1904EAI
MAX1904ETJ
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
28 SSOP
32 Thin QFN 5mm x 5mm
28 SSOP
32 Thin QFN 5mm x 5mm
28 SSOP
32 Thin QFN 5mm x 5mm
________________________Applications
Notebook and Subnotebook Computers
PDAs and Mobile Communicators
Desktop CPU Local DC-DC Converters
3.3V
INPUT
5V (RTC)
Functional Diagram
12V
5V
LINEAR
12V
LINEAR
3.3V
SMPS
5V
SMPS
5V
Idle Mode is a trademark of Maxim Integrated Products, Inc.
Dual Mode is a trademark of Maxim Integrated Products, Inc.
Pin Configurations appear at end of data sheet.
ON/OFF
POWER-UP
SEQUENCE
POWER-
GOOD
RESET
________________________________________________________________
Maxim Integrated Products
1
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.
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
