LM3687 DC-DC Converter Datasheet

LM3687 Datasheet, PDF, Equivalent


Part Number

LM3687

Description

Step-Down DC-DC Converter

Manufacture

etcTI

Total Page 30 Pages
Datasheet
Download LM3687 Datasheet


LM3687
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 VIN_LIN 4.5V
• 10µA Typical IQ from VIN_LIN
• 350mA Maximum Load Capability
Combined Common Features:
• 65µA typical Quiescent Current from VBATT 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

LM3687
LM3687
SNVS473B – DECEMBER 2007 – REVISED MAY 2013
www.ti.com
DESCRIPTION (CONTINUED)
Two enable pins allow the separate operation of either the DC-DC or the Linear Regulator alone or both. If the
power input voltage for the Linear Regulator VIN_LIN is not sufficiently high (e.g. the DC-DC converter is not
enabled or starting up) a startup LDO supplies the Linear Regulator Output from VBATT for 50mA rated load
current (Startup Mode). If VIN_LIN is at the required voltage level, the startup LDO is deactivated and the main
regulator provides 350mA output current. In shutdown mode (Enable pins pulled low) the device turns off and
reduces battery consumption to 0.1µA (typ.).
The LM3687 is available in a tiny, lead-free (NO PB) 9-bump DSBGA package. A high switching frequency of
1.8MHz (typ.) allows the use of tiny surface-mount components. Only four external components -one inductor
and three ceramic capacitors- are required.
Typical Application Circuit
EN_DCDC
B2
LM3687
EN_LIN
C3
A2
SGND
VBATT
C1
FB_DCDC
C2
SW
B1
2.2 PH
1.8V
2.7...5.5V
4.7 PF
PGND
A1
10 PF
Load
DC-DC
0..750 mA
Li-Ion
or
3 cell
NiMH/
NiCd
VIN_LIN
B3
VOUT_LIN
A3
2.2 PF
1.5V
Load
LIN
0..350 mA
Figure 1. Typical Application Circuit: Linear Regulator as Post Regulator
EN_DCDC
B2
LM3687
EN_LIN
C3
A2
SGND
VBATT
C1
FB_DCDC
C2
SW
B1
2.2 PH
4.7 PF
PGND
A1
10 PF
2.7...5.5V
Load
DC-DC
0..750 mA
Li-Ion
or
3 cell
NiMH/
NiCd
VIN_LIN
B3
VOUT_LIN
A3
1.0 PF
2.2 PF
Load
LIN
0..350 mA
Figure 2. Typical Application Circuit: Independent Mode of Operation
Connection Diagram
2 Submit Documentation Feedback
Product Folder Links: LM3687
Copyright © 2007–2013, Texas Instruments Incorporated


Features LM3687 www.ti.com SNVS473B – DECEMBE R 2007 – REVISED MAY 2013 LM3687 Ste p-Down DC-DC Converter with Integrated Low Dropout Regulator and Startup Mode Check for Samples: LM3687 FEATURES 1 2 DC-DC Converter: • 750mA Maximum Load Capability • 1.8MHz PWM Fixed Switch ing Frequency (Typ.) • Automatic PFM/ PWM Mode Switching • 27µA typ. Quies cent Current • Internal Synchronous R ectification for High Efficiency • In ternal Soft Start Dual Rail Linear Regu lator: • Startup Mode • Load Transi ents < 25mVpeak Typ. • Line Transient s < 1mVpeak Typ. • Very Low Dropout V oltage: 82mV Typ. at 350mA Load Current • 0.7V ≤ VIN_LIN ≤ 4.5V • 10µ A Typical IQ from VIN_LIN • 350mA Max imum Load Capability Combined Common Fe atures: • 65µA typical Quiescent Cur rent from VBATT if Both Regulators are Enabled • 750mA Maximum Combined Load Capability in Post Regulation Setup (D C-DC 400mA + Linear Regulator 350mA) 1100mA Maximum Total Load Capability in Independent Mode of Operation (DC-DC: 750mA, Linear Regulator: 3.
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