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PDF LM3686TLX-AADW Data sheet ( Hoja de datos )
| Número de pieza | LM3686TLX-AADW | |
| Descripción | Step-Down DC-DC Converter | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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September 10, 2008
LM3686
Step-Down DC-DC Converter with Integrated Post Linear
Regulators System and Low-Noise Linear Regulator
General Description
The LM3686 is a step-down DC-DC converter with one inte-
grated 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 pro-
vides 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 rectifi-
cation 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 VBATT with maximal 50 mA.
In the combined operation where both enables are raised to-
gether, 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 re-
duces battery consumption to 2.5 μA (typ.).
The LM3686 is available in a 12-bump micro SMD package.
A high-switching frequency of 3 MHz (typ.) allows the use of
a few tiny surface-mount components. Only six external sur-
face-mount components, an inductor and five ceramic capac-
itors, are required to establish a 15.66 mm2 total solution size.
Features
DC-DC REGULATOR:
■ VOUT_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.
■ VOUT_LILO = 0.7V to 2.0V ( in 50 mV steps - factory
programmed )
■ 70 µA typical IQ from VIN_LILO
■ 350 mA Maximum Load Capability (Large FET)
LINEAR REGULATOR: LDO
■ Load transients < 80 mV peak typ.
■ Line transients < 1 mV peak typ.
■ VOUT_LDO = 1.5V to 3.3V ( in 100 mV steps - factory
programmed )
■ 50µA typical IQ
■ 300 mA Maximum Load Capability
COMBINED GLOBAL FEATURES:
■ VBATT ≥ VOUT_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 VBATT
■ 15.66mm2 total solution size
Applications
■ Moblie TV
■ Hand-Held Radios
■ Personal Digital Assistants
■ Palm-top PCs
■ Portable Instruments
■ Battery-Powered Devices
■ Portable Personal Clients
© 2008 National Semiconductor Corporation 300255
www.national.com
1 page  
Enable Combinations
EN_DCDC
0
0
0
1
1
EN_LILO
0
0
1
0
1
11
EN_LDO
0
1
0
0
0
1
Function
No Outputs
Linear Regulator enabled only (EN_LDO), supply from VIN_LDO,
IOUT_MAX = 300 mA
Linear Regulator enabled only LILO supplies from VIN_LDO,
IOUT_MAX = 50 mA, VIN_LDO > = VOUT_LILO
DC-DC converter enabled only
Linear Regulator & DCDC enabled
1) VIN_LILO < VOUT_LILO + 150 mV (typ.), the small NMOS device is active
(IMAX = 50 mA) and supplied by VIN_LDO.
2) If VIN_LILO > VOUT_LILO + 250 mV (typ.), the large NMOS device is active
(IMAX = 350 mA) and supplied by VIN_LILO. Maxium current of DC-DC when
EN_LILO = High is 250 mA (Note A & B)
DC-DC converter and linear regulator active.
Linear regulator starts after DC-DC converter.
Note A: The LILO is turned on via a small NMOS device sup-
plied by VIN_LDO . The maximum current is 50 mA when this
small NMOS is ON. If higher current > 50 mA is desired the
following condition must be done: EN_DC = HIGH .
Note B: When the switcher is enabled, a transition occurs
from the small NMOS to a larger NMOS. The transition occurs
when VIN_LILO > VOUT_LILO + 250 mV. If VIN_LILO < VOUT_LILO +
150 mV, the LILO switches back to small NMOS (Switcher EN
= low).
FIGURE 3. Mode Transition
30025532
5 www.national.com
5 Page 
Switching Frequency vs. Temperature
Current Limit vs. Temperature (Open Loop)
RDSON vs. Temperature
30025537
30025538
Startup (all three enables tied together)
30025539
VBATT Line Transient Response
Line Transient Response
30025524
30025525
11
30025518
www.national.com
11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet LM3686TLX-AADW.PDF ] | |
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