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PDF LM3671 Data sheet ( Hoja de datos )
| Número de pieza | LM3671 | |
| Descripción | 2MHz / 600mA Step-Down DC-DC Converter in SOT23-5 | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LM3671 (archivo pdf) en la parte inferior de esta página. Total 16 Páginas | ||
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November 2004
LM3671
2MHz , 600mA Step-Down DC-DC Converter in SOT23-5
General Description
The LM3671 step-down DC-DC converter is optimized for
powering ultra-low voltage circuits from a single Li-Ion cell or
3 cell NiMH/NiCd batteries. It provides up to 600mA load
current, over an input voltage range from 2.8V to 5.5V. There
are several different fixed voltage output options available as
well as an adjustable output voltage version.
The device offers superior features and performance for
mobile phones and similar portable applications with com-
plex power management systems. Automatic intelligent
switching between PWM low-noise and PFM low-current
mode offers improved system control. During full-power op-
eration, a fixed-frequency 2 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 16 µA (typ) at light loads and system standby.
Internal synchronous rectification provides high efficiency. In
shutdown mode (Enable pin pulled low) the device turns off
and reduces battery consumption to 0.01 µA (typ).
The LM3671 is available in a SOT23-5 package with Pb and
No Pb (Lead free) versions. A high switching frequency - 2
MHz (typ) - allows use of tiny surface-mount components.
Only three external surface-mount components, an inductor
and two ceramic capacitors, are required.
n 2 MHz PWM fixed switching frequency (typ)
n Automatic PFM/PWM mode switching
n Available in fixed output voltages and adjustable version
n SOT23-5 package
n Internal synchronous rectification for high efficiency
n Internal soft start
n 0.01 µA typical shutdown current
n Operates from a single Li-Ion cell or 3 cell NiMH/NiCd
batteries
n Only three tiny surface-mount external components
required (one inductor, two ceramic capacitors)
n Current overload and Thermal shutdown protection
Applications
n Mobile phones
n PDAs
n MP3 players
n W-LAN
n Portable instruments
n Digital still cameras
n Portable Hard disk drives
Features
n 16 µA typical quiescent current
n 600 mA maximum load capability
Typical Application Circuits
FIGURE 1. Typical Application Circuit
20108401
© 2004 National Semiconductor Corporation DS201084
www.national.com
1 page  
Electrical Characteristics (Notes 2, 9, 10) Limits in standard typeface are for TJ = 25˚C. Limits in boldface
type apply over the full operating junction temperature range (−25˚C ≤ TJ ≤ +125˚C). Unless otherwise noted, specifications
apply to the LM3671 Typical Application Circuit (Figure. 1) with VIN = EN = 3.6V, VOUT = 1.5V (Continued)
Note 8: Refer to datasheet curves for closed loop data and its variation with regards to supply voltage and temperature. Electrical Characteristic table reflects open
loop data (FB=0V and current drawn from SW pin ramped up until cycle by cycle current limit is activated). Closed loop current limit is the peak inductor current
measured in the application circuit by increasing output current until output voltage drops by 10%.
Note 9: Min and Max limits are guaranteed by design, test or statistical analysis. Typical numbers are not guaranteed, but do represent the most likely norm.
Note 10: The parameters in the electrical characteristic table are tested at VIN= 3.6V unless otherwise specified. For performance over the input voltage range refer
to datasheet curves.
Note 11: Input voltage range for all voltage options is 2.8V to 5.5V. The voltage range recommended (Fixed Voltage parts) for ideal applications performance with
500mA or higher output current is given below.
VIN = 2.8V to 4.5V for VOUT = 1.2V, 1.25V, 1.375V, 1.5V and 1.6V.
VIN = 3.0V to 4.5V for VOUT = 1.8V and 1.875V.
Dissipation Rating Table
θJA
250˚C/W
TA≤ 25˚C
Power Rating
400mW
TA= 60˚C
Power Rating
260mW
TA= 85˚C
Power Rating
160mW
5 www.national.com
5 Page 
Operation Description (Continued)
20108422
FIGURE 6. Typical PFM Operation
During PFM operation, the converter positions the output
voltage slightly higher than the nominal output voltage during
PWM operation, allowing additional headroom for voltage
drop during a load transient from light to heavy load. The
PFM comparators sense the output voltage via the feedback
pin and control the switching of the output FETs such that the
output voltage ramps between ~0.6% and ~1.7% above the
nominal PWM output voltage. If the output voltage is below
the ‘high’ PFM comparator threshold, the PMOS power
switch is turned on. It remains on until the output voltage
reaches the ‘high’ PFM threshold or the peak current ex-
ceeds the IPFM level set for PFM mode. The typical peak
current in PFM mode is: IPFM = 112mA + VIN/27Ω .
Once the PMOS power switch is turned off, the NMOS
power switch is turned on until the inductor current ramps to
zero. When the NMOS zero-current condition is detected,
the NMOS power switch is turned off. If the output voltage is
below the ‘high’ PFM comparator threshold (see Figure 7),
the PMOS switch is again turned on and the cycle is re-
peated until the output reaches the desired level. Once the
output reaches the ‘high’ PFM threshold, the NMOS switch is
turned on briefly to ramp the inductor current to zero and
then both output switches are turned off and the part enters
an extremely low power mode. Quiescent supply current
during this ‘sleep’ mode is 16µA (typ), which allows the part
to achieve high efficiencies under extremely light load con-
ditions. When the output drops below the ‘low’ PFM thresh-
old, the cycle repeats to restore the output voltage (average
voltage in pfm mode) to ∼1.15% above the nominal PWM
output voltage.
If the load current should increase during PFM mode (see
Figure 7) causing the output voltage to fall below the ‘low2’
PFM threshold, the part will automatically transition into
fixed-frequency PWM
sitions from PWM to
PmFoMdem. WodheenatV~IN3=5m2.A8Votuhtepuptacrturtrraenn-t
and from
PWM to
PFM
PFM
to PWM
transition
mhoadpepeants~8a5t m~A50,mwAheanndVIPN=F3M.6Vto,
PtoWPMFMtrantrsaintiosintiohnaphpaepnpseants~1a0t 0~m6A5m, wAheanndVIPNF=M4.5tVo,
PWM
PWM
transition happens at ~115mA.
FIGURE 7. Operation in PFM Mode and Transfer to PWM Mode
20108403
SHUTDOWN MODE
Setting the EN input pin low (<0.4V) places the LM3671 in
shutdown mode. During shutdown the PFET switch, NFET
switch, reference, control and bias circuitry of the LM3671
are turned off. Setting EN high (>1.0V) enables normal
operation. While turning on the device with EN, soft start is
activated. It is recommended to set EN pin low to turn off the
LM3671 during system power up and undervoltage condi-
11 www.national.com
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LM3671.PDF ] | |
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