Rainbow Electronics MAX8742 - Manual

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General Description
The MAX8741/MAX8742 are buck-topology, step-down,
switch-mode, power-supply controllers that generate
logic-supply voltages in battery-powered systems. These
high-performance, dual/triple-output devices include on-
board power-up sequencing, power-good signaling with
delay, digital soft-start, secondary winding control, low-
dropout circuitry, internal frequency-compensation net-
works, 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 MAX8741/MAX8742 include two PWM regulators,
adjustable from 2.5V to 5.5V with fixed 5.0V and 3.3V
modes. All these devices include secondary feedback
regulation, and the MAX8742 contains a 12V/120mA lin-
ear regulator. The MAX8741 includes a secondary feed-
back 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 MAX8741/MAX8742 contain internal output overvolt-
age- and undervoltage-protection features.
________________________Applications
Notebook and Subnotebook Computers
PDAs and Mobile Communicators
Desktop CPU Local DC-DC Converters
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 (MAX8741)
♦ 5V/50mA Linear-Regulator Output
♦ Precision 2.5V Reference Output
♦ Programmable Power-Up Sequencing
♦ Power-Good ( RESET ) Output
♦ Output Overvoltage Protection
♦ Output Undervoltage Shutdown
♦ 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
MAX8741/
M
AX8742
500kHz Multi-Output Power-Supply Controllers
with High Impedance in Shutdown
________________________________________________________________ Maxim Integrated Products 1
5V
LINEAR
12V
LINEAR
POWER-UP
SEQUENCE POWER-
GOOD
3.3V
SMPS
5V
SMPS
RESET ON/OFF
5V (RTC)
3.3V
INPUT
5V
12V
Functional Diagram
19-3262; Rev 0; 4/04
Ordering Information
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.
PART TEMP RANGE PIN-PACKAGE
MAX8741 EAI -40
°
C to +85
°
C 28 SSOP
MAX8741ETJ -40
°
C to +85
°
C 32 Thin QFN 5m m x 5m m
MAX8742 EAI -40
°
C to +85
°
C 28 SSOP
MAX8742ETJ -40
°
C to +85
°
C 32 Thin QFN 5m m x 5m m