LM3686_14 Datasheet, PDF (1/28 Pages) Texas Instruments – Step-Down DC-DC Converter with Integrated Post Linear Regulators System and Low-Noise Linear Regulator

LM3686
www.ti.com
SNVS520D – AUGUST 2008 – REVISED MARCH 2011
LM3686 Step-Down DC-DC Converter with Integrated Post Linear Regulators System and
Low-Noise Linear Regulator
Check for Samples: LM3686
FEATURES
1
2DC-DC REGULATOR
• V_{OUT_DCDC} = 1.2V to 2.5V ( in 100 mV steps -
factory programmed )
• 600 mA maximum load capability (LILO = OFF)
• 3 MHz PWM fixed switching frequency (typ.)
• Automatic PFM/PWM mode switching
• Internal synchronous rectification for high
efficiency
• Internal soft start
DUAL RAIL LINEAR REGULATOR: LILO
• Load transients < 50 mV peak typ.
• Line transients < 1 mV peak typ.
• V_{OUT_LILO} = 0.7V to 2.0V ( in 50 mV steps -
factory programmed )
• 70 µA typical I_Q from V_{IN_LILO}
• 350 mA Maximum Load Capability (Large FET)
LINEAR REGULATOR: LDO
• Load transients < 80 mV peak typ.
• Line transients < 1 mV peak typ.
• V_{OUT_LDO} = 1.5V to 3.3V ( in 100 mV steps -
factory programmed )
• 50 µA typical I_Q
• 300 mA Maximum Load Capability
COMBINED GLOBAL FEATURES
• V_BATT ≥ V_{OUT_LILO} + 1.5V or 2.7V, whichever is
higher
• 900 mA maximum combined load capability
• Operates from a single Li-Ion cell or 3 cell
NiMH/NiCd batteries
• Only six tiny surface-mount external
components required (one inductor, five
ceramic capacitors)
• 12–bump micro SMD
• 100 µA Iq from V_BATT
• 15.66 mm² total solution size
APPLICATIONS
• Moblie TV
• Hand-Held Radios
• Personal Digital Assistants
• Palm-top PCs
• Portable Instruments
• Battery-Powered Devices
• Portable Personal Clients
DESCRIPTION
The LM3686 is a step-down DC-DC converter with one integrated very low dropout linear regulator and a low
noise linear regulator optimized for powering ultra-low voltage circuits from a single Li-Ion cell or 3 cell
NiMH/NiCd batteries. It provides three outputs with combined load current up to 900 mA over an input voltage
range from 2.7V to 5.5V.
The device offers superior features and performance for many applications. Automatic intelligent switching
between PWM low-noise and PFM low-current mode offers improved system control. During full-power operation,
a fixed-frequency 3 MHz (typ.), PWM mode drives loads from ~70 mA to 600 mA max. Hysteretic PFM mode
extends the battery life through reduction of the quiescent current to 28 μA (typ.) at light load and system
standby. Internal synchronous rectification provides high efficiency.
Three enable pins allow the separate operation of either the DC-DC, post-regulation linear regulator or the linear
regulator alone. If the DC-DC is not enabled during startup of the post-regulation linear regulator, a parallel small
pass transistor supplies the linear regulator from V_BATT with maximal 50 mA. In the combined operation where
both enables are raised together, the small pass transistor is deactivated and the big pass transistor provides
350 mA output current. In shutdown mode (Enable pins pulled low), the device turns off and reduces battery
consumption to 2.5 μA (typ.).
1
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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 © 2008–2011, Texas Instruments Incorporated