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PDF LM3687 Data sheet ( Hoja de datos )
| Número de pieza | LM3687 | |
| Descripción | Step-Down DC-DC Converter | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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December 4, 2007
LM3687
Step-Down DC-DC Converter with Integrated Low Dropout
Regulator and Startup Mode
General Description
The LM3687 is a step-down DC-DC converter with an inte-
grated 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 out-
put voltages and combined load current up to 750mA in post
www.DataSheerte4gUu.claotmion mode or 1100mA in independent mode of opera-
tion, over an input voltage range from 2.7V to 5.5V. There are
several different fixed output voltage combinations available
(refer to table 'Voltage Options').
The Linear Regulator being driven from the fixed output volt-
age of the buck converter (post regulation) translates to high
efficiency.
The device offers superior features and performance for mo-
bile 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.
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
micro SMD 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.
Features
DC-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 micro SMD 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
© 2007 National Semiconductor Corporation 202101
www.national.com
1 page  
Absolute Maximum Ratings (Notes 2, 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
VIN_LIN, VBATT pins: Voltage to GND,
VIN_LIN≤ VBATT
VIN_LIN pin to VBATT pin
Enable pins,
Feedback pin,
SW pin
Continuous Power Dissipation
(Note 3)
Junction Temperature (TJ-MAX )
Storage Temperature Range
Package Peak Reflow Temperature
www.DataS(Phbe-efrt4eUe,.c1o0m-20 sec.) (Note 4)
ESD Rating (Note 5)
Human Body Model:
Machine Model
-0.2V to 6.0V
0.2V
(GND-0.2V) to
(VBATT+0.2V) with
6.0V max
Internally Limited
150°C
-65°C to + 150°C
260°C
2.0kV
200V
Operating Ratings
(Notes 1, 2)
Input Voltage Range VBATT
(Note 12)
Input Voltage Range VIN_LIN
Junction Temperature (TJ) Range
Ambient Temperature (TA) Range
(Note 6)
2.7V to 5.5V
≥( VOUT_LIN(NOM) + 1.5V
and
≥VOUT_DCDC(NOM) +
1.0V)
(VOUT_LIN(NOM) + 0.25V)
to 4.5V
-30°C to + 125°C
-30°C to + 125°C
Thermal Properties
Junction-to-Ambient Thermal
Resistance (θJA), for 4 layer board
(Note 7)
Micro SMD 9
70°C/W
ESD Caution Notice
National Semiconductor recommends that all integrated circuits be handled with appropriate precautions. Failure to observe proper
ESD handling techniques can result in damage.
Electrical Characteristics (Notes 2, 8) Typical values and limits appearing in standard typeface are for TA =
25°C. Limits appearing in boldface type apply over the full operating temperature range: -30°C ≤ TJ ≤ +125°C. Unless otherwise
noted, VIN_LIN = VOUT_LIN(NOM) + 0.3V, VBATT = 3.6V, IOUT_LIN = 1mA, VEN_DCDC = VEN_LIN = VBATT, CVBATT = 4.7µF, CVOUT_DCDC =
10µF, CVOUT_LIN = 2.2µF, CVIN_LIN = 1.0µF, L = 2.2µH.
DC-DC Converter (Note 11)
Symbol
Parameter
Conditions
Typical
VFB_DCDC
Feedback Voltage
Accuracy
Line Regulation
PWM Mode
VOUT_DCDC + 1.0V ≤ VBATT ≤ 5.5V, IOUT_DCDC
= 150mA
0.06
Limit
Min Max
-2.5 +2.5
Units
%
%/V
RDSON(P)
Load Regulation
100mA ≤ IOUT_DCDC ≤ 750mA
Pin-Pin Resistance for
PFET
0.0005
280
%/mA
500 mΩ
RDSON(N)
ILIM_DCDC
FOSC
Pin-Pin Resistance for
NFET
Switch Peak Current Open loop (Note 14)
Limit
Internal Oscillator
Frequency
PWM Mode
200 400 mΩ
1172 994 1380 mA
1.8 1.3 2.3 MHz
5 www.national.com
5 Page 
Efficiency DC-DC vs. Output Current
LDO disabled
Startup into no load
www.DataSheet4U.com
Startup into load
20210134
20210115
VBATT Line Transient Response (PWM Mode)
VIN_LIN Line Transient Response
20210116
Load Transient Response DC-DC
(PWM Mode: 100mA to 750mA)
20210117
20210118
11
20210119
www.national.com
11 Page | ||
| Páginas | Total 22 Páginas | |
| PDF Descargar | [ Datasheet LM3687.PDF ] | |
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