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PDF LTC3405A-1.375 Data sheet ( Hoja de datos )
| Número de pieza | LTC3405A-1.375 | |
| Descripción | 1.375V / 1.5MHz - 300mA Synchronous Step-Down Regulators in ThinSOT | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTCw3w4w.0Da5taAShe-e1t4U..3co7m 5
1.375V, 1.5MHz, 300mA
Synchronous Step-Down
Regulators in ThinSOT
FEATURES
■ High Efficiency: Up to 90%
■ Very Low Quiescent Current: Only 20µA
During Operation
■ 300mA Output Current at VIN = 3V
■ 2.5V to 5.5V Input Voltage Range
■ 1.5MHz Constant Frequency Operation
■ No Schottky Diode Required
■ Low Dropout Operation: 100% Duty Cycle
■ Stable with Ceramic Capacitors
■ Shutdown Mode Draws < 1µA Supply Current
■ ±3% Output Voltage Accuracy
■ Current Mode Operation for Excellent Line and
Load Transient Response
■ Overtemperature Protected
■ Low Profile (1mm) ThinSOTTM Package
U
APPLICATIO S
■ Cellular Telephones
■ Personal Information Appliances
■ Wireless and DSL Modems
■ Digital Still Cameras
■ MP3 Players
■ Portable Instruments
DESCRIPTIO
The LTC®3405A-1.375 is a high efficiency monolithic
synchronous buck regulator using a constant frequency,
current mode architecture. Supply current during opera-
tion is only 20µA and drops to <1µA in shutdown. The 2.5V
to 5.5V input voltage range makes the LTC3405A-1.375
ideally suited for single Li-Ion battery-powered applica-
tions. 100% duty cycle provides low dropout operation,
extending battery life in portable systems.
Switching frequency is internally set at 1.5MHz, allowing
the use of small surface mount inductors and capacitors.
The LTC3405A-1.375 is specifically designed to work well
with ceramic output capacitors, achieving very low output
voltage ripple and a small PCB footprint.
The internal synchronous switch increases efficiency and
eliminates the need for an external Schottky diode. The
LTC3405A-1.375 is available in a low profile (1mm)
ThinSOT package.
For other output voltages, refer to the LTC3405A and
LTC3405A-1.5/LTC3405A-1.8 data sheets.
, LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode
is a registered trademark of Linear Technology Corporation. ThinSOT is a trademark of
Linear Technology Corporation. All other trademarks are the property of their respective
owners. Protected by U.S. Patents, including 5481178, 6580258, 6304066, 6127815,
6498466, 6611131.
TYPICAL APPLICATIO
VIN
2.7V
TO 5.5V
CIN
4.7µF
CER
VIN SW
LTC3405A-1.375
4.7µH
RUN
MODE VOUT
GND
3405A1375 F01
COUT
4.7µF
CER
VOUT
1.375V
300mA
Figure 1a. High Efficiency Step-Down Converter
100
90
80
70
60
50
40
30
0.1
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
VIN = 5.5V
1 10 100
OUTPUT CURRENT (mA)
1000
3405A1375 F01b
Figure 1b. Efficiency vs Load Current
3405a1375f
1
1 page  
LTCw3w4w.0Da5taAShe-e1t4U..3co7m 5
TYPICAL PERFOR A CE CHARACTERISTICS TA = 25°C unless otherwise noted.
(From Figure 1a)
Load Step
VOUT
100mV/DIV
AC
COUPLED
IL
200mA/DIV
ILOAD
200mA/DIV
VIN = 3.6V
20µs/DIV
ILOAD = 20mA TO 250mA
PULSE SKIPPING MODE
Load Step
VOUT
100mV/DIV
AC
COUPLED
IL
200mA/DIV
ILOAD
200mA/DIV
3405A1375 G17
VIN = 3.6V
20µs/DIV
ILOAD = 20mA TO 250mA
Burst Mode OPERATION
Load Step
VOUT
100mV/DIV
AC
COUPLED
IL
200mA/DIV
ILOAD
200mA/DIV
3405A1375 G18
VIN = 3.6V
20µs/DIV
ILOAD = 0mA TO 250mA
Burst Mode OPERATION
3405A1375 G19
PI FU CTIO S
RUN (Pin 1): Run Control Input. Forcing this pin above
1.5V enables the part. Forcing this pin below 0.3V shuts
down the device. In shutdown, all functions are disabled
drawing <1µA supply current. Do not leave RUN floating.
GND (Pin 2): Ground Pin.
SW (Pin 3): Switch Node Connection to Inductor. This pin
connects to the drains of the internal main and synchro-
nous power MOSFET switches.
VIN (Pin 4): Main Supply Pin. Must be closely decoupled
to GND, Pin 2, with a 2.2µF or greater ceramic capacitor.
VOUT (Pin 5): Output Voltage Feedback Pin. An internal
resistive divider divides the output voltage down for com-
parison to the internal 0.9V reference voltage.
MODE (Pin 6): Mode Select Input. To select pulse skip-
ping mode, tie to VIN. Grounding this pin selects Burst
Mode operation. Do not leave this pin floating.
3405a1375f
5
5 Page 
APPLICATIO S I FOR ATIO
Substituting VOUT = 1.375V, VIN = 4.2V, ∆IL = 60mA and
f = 1.5MHz in equation (3) gives:
L
=
1.375V
1.5MHz(60mA)
⎛
⎝⎜1−
1.375V
4.2V
⎞
⎠⎟
≅
10µH
VOUT
PIN 1
L1 SW
VIA TO VIN
LTC3405A-1.375
VIN
COUT
GND
CIN
3405A1518 F04
Figure 4. LTC3405A-1.375 Suggested Layout
For best efficiency choose a 200mA or greater inductor
with less than 0.3Ω series resistance.
CIN will require an RMS current rating of at least 0.125A
≅ ILOAD(MAX)/2 at temperature and COUT will require an
ESR of less than 0.5Ω. In most cases, a ceramic capacitor
will satisfy this requirement.
Figure 5 shows the complete circuit along with its effi-
ciency curve.
VIN
2.7V
TO 4.2V
CIN***
2.2µF
CER
4
VIN
3 10µH*
SW
VOUT
1.375V
LTC3405A-1.375
1
RUN
6
MODE
5
VOUT
COUT**
10µF
CER
GND * MURATA LQHMCN10002
** MURATA 0603 GRM188R60G106ME47B
2 *** MURATA 0603 GRM188R61A225KE34B
3405A1375 F05a
Figure 5a. Small Footprint Application
LTCw3w4w.0Da5taAShe-e1t4U..3co7m 5
100
90
80
70
60
50
40
30
20
10
0
0.1
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
1 10 100
LOAD CURRENT (mA)
1000
3405A1375 F05b
Figure 5b. LTC3405A-1.375 Small Footprint Efficiency
VOUT
100mV/DIV
AC
COUPLED
IL
200mA/DIV
ILOAD
200mA/DIV
VIN = 3.6V
20µs/DIV
ILOAD = 100mA TO 300mA
Burst Mode OPERATION
Figure 5c.
3405A1375 F05c
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
3405a1375f
11
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| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet LTC3405A-1.375.PDF ] | |
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