LM3687_15 Datasheet, PDF (1/30 Pages) Texas Instruments – Step-Down DC-DC Converter

LM3687
www.ti.com
SNVS473B – DECEMBER 2007 – REVISED MAY 2013
LM3687 Step-Down DC-DC Converter with Integrated Low Dropout Regulator and Startup
Mode
Check for Samples: LM3687
FEATURES
1
2DC-DC Converter:
• 750mA Maximum Load Capability
• 1.8MHz PWM Fixed Switching Frequency
(Typ.)
• Automatic PFM/PWM Mode Switching
• 27µA typ. Quiescent Current
• Internal Synchronous Rectification for High
Efficiency
• Internal Soft Start
Dual Rail Linear Regulator:
• Startup Mode
• Load Transients < 25mVpeak Typ.
• Line Transients < 1mVpeak Typ.
• Very Low Dropout Voltage: 82mV Typ. at
350mA Load Current
• 0.7V ≤ V_{IN_LIN} ≤ 4.5V
• 10µA Typical I_Q from V_{IN_LIN}
• 350mA Maximum Load Capability
Combined Common Features:
• 65µA typical Quiescent Current from V_BATT if
Both Regulators are Enabled
• 750mA Maximum Combined Load Capability in
Post Regulation Setup (DC-DC 400mA + Linear
Regulator 350mA)
• 1100mA Maximum Total Load Capability in
Independent Mode of Operation (DC-DC:
750mA, Linear Regulator: 350mA)
• Operates from a Single Li-Ion Cell or 3 Cell
NiMH/NiCd Batteries
• Only Four Tiny Surface-Mount External
Components Required (One Inductor, Three
Ceramic Capacitors)
• Small 9-Bump DSBGA Package
• Over-Temperature, Current Overload and
Under-Voltage Protection
APPLICATIONS
• Mobile Phones
• Hand-Held Radios
• Personal Digital Assistants
• Palm-top PCs
• Portable Instruments
• Battery Powered Devices
DESCRIPTION
The LM3687 is a step-down DC-DC converter with an
integrated low dropout Linear Regulator optimized for
powering ultra-low voltage circuits from a single Li-Ion
cell or 3 cell NiMH/NiCd batteries. It provides a dual
output with fixed output voltages and combined load
current up to 750mA in post regulation mode or
1100mA in independent mode of operation, over an
input voltage range from 2.7V to 5.5V. There are
several different fixed output voltage combinations
available (refer to Voltage Options).
The Linear Regulator being driven from the fixed
output voltage of the buck converter (post regulation)
translates to high efficiency.
The device offers superior features and performance
for mobile phones and similar portable applications
with complex power management systems. Automatic
intelligent switching between PWM low-noise and
PFM low-current mode offers improved efficiency
over the full load current range. During full-power
operation, a fixed-frequency 1.8MHz (typ.) PWM
mode drives loads from ~80mA to 750mA max.
Hysteretic PFM mode extends the battery life through
reduction of the quiescent current during light loads
and system standby.
The LM3687 also features internal protection against
over-temperature, current overload and under-voltage
conditions.
1
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
All trademarks are the property of their respective owners.
2
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2007–2013, Texas Instruments Incorporated