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PDF LTC3541-3 Data sheet ( Hoja de datos )
| Número de pieza | LTC3541-3 | |
| Descripción | High Efficiency Buck + VLDO Regulator | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LTC3541-3 (archivo pdf) en la parte inferior de esta página. Total 20 Páginas | ||
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FEATURES
■ High Efficiency 500mA Buck Plus 300mA VLDO
Regulator
Auto Start-Up Powers VLDO/Linear Regulator
Output Prior to Buck Output
■ Independent 500mA High Efficiency Buck
(VIN: 2.7V to 5.5V)
■ 300mA VLDO Regulator with 30mA Standalone Mode
www■. DaNtoaSEhxeteetr4nUa.cloSmchottky Diodes Required
■ Fixed Buck Output Voltage: 1.8V
■ VLDO Input Voltage Range (LVIN: 1.675V to 5.5V)
■ Fixed VLDO Output Voltage: 1.575V
■ Selectable Fixed Frequency, Pulse-Skip Operation
or Burst Mode® Operation
■ Short-Circuit Protected
■ Current Mode Operation for Excellent Line and Load
Transient Response
■ Shutdown Current: <3µA
■ Constant Frequency Operation: 2.25MHz
■ Low Dropout Buck Operation: 100% Duty Cycle
■ Small, Thermally Enhanced, 10-Lead (3mm × 3mm)
APDFPNLPIaCckAagTeIOUS
■ Digital Cameras
■ Cellular Phones
■ PC Cards
■ Wireless and DSL Modems
■ Other Portable Power Systems
LTC3541-3
High Efficiency
Buck + VLDO Regulator
DESCRIPTIO
The LTC®3541-3 combines a synchronous buck DC/
DC converter with a very low dropout linear regulator
(VLDOTM regulator)andinternalfeedbackresistornetworks
to provide two output voltages from a single input voltage
with minimum external components. When configured
for dual output operation, the LTC3541-3’s auto start-up
feature will bring the 1.575V VLDO/linear regulator output
into regulation in a controlled manner prior to enabling the
1.8V buck output without the need for external pin control.
The 300mA VLDO/linear regulator output will source only
30mA until the buck output achieves regulation. The input
voltage range is ideally suited for applications powered
from a Li-Ion battery and 5V or 3.3V rails.
The synchronous buck converter provides a high efficiency
output, typically 90%. It can provide up to 500mA of output
current while switching at 2.25MHz, allowing the use of
small surface mount inductors and capacitors. A mode
select pin allows Burst Mode operation to be enabled for
higher efficiency at light load currents, or disabled for lower
noise, constant frequency operation.
The VLDO regulator provides a low noise, low voltage
output capable of providing up to 300mA of output current
using only a 2.2µF ceramic capacitor. The input supply
voltage of the VLDO regulator (LVIN) may come from the
buck regulator or a separate supply.
, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology
Corporation. VLDO is a trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Protected by U.S. Patents, including 5481178, 6611131, 6304066, 6498466, 6580258.
TYPICAL APPLICATIO
LTC3541-3 Typical Application
VIN
3V TO 5V
2.2µH
VOUT1
1.8V
10µF
SW ENVLDO
VIN MODE
LTC3541-3
ENBUCK GND
VOUT
LVIN LVOUT
PGND
VOUT2
1.575V
2.2µF
35413 TA01a
Buck (Burst) Efficiency vs Load Current
100
90
VIN = 3V
80 EFFICIENCY
70
1
0.1
60
50
POWER
LOSS
0.01
40
30
0.001
20
10
0 0.0001
1 10 100 1000
LOAD CURRENT (mA)
35413 TA01b
35413fc
1 page  
TYPICAL PERFOR A CE CHARACTERISTICS
LTC3541-3
VLDO/Linear Regulator vs
Temperature
0.410
0.408 VIN = 3.6V
0.406
0.404
0.402
0.400
0.398
0.396
www.D0a.3t9a4Sheet4U.com
0.392
0.390
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
35413 G19
Buck (Burst) and VLDO Output
Buck Reference vs Temperature
0.820
0.816
VIN = 3.6V
0.812
0.808
0.804
0.800
0.796
0.792
0.788
0.784
0.780
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
35413 G20
Buck (Pulse Skip) Load Step from
1mA to 500mA
RDS(0N) vs Temperature
0.700
0.600
0.500
0.400
SYNCH SWITCH
0.300
0.200
0.100 MAIN SWITCH
VIN = 2.5V
VIN = 3.6V
0 VIN = 5.5V
–50 –25 0 25 50 75 100 125
TEMPERATURE (°C)
35413 G10
Buck (Burst) Load Step from 1mA
to 500mA
LVOUT
10mV/DIV
AC COUPLED
VOUT
10mV/DIV
AC COUPLED
VIN = 3.6V
2µs/DIV
LVOUT = 1.5V
VOUT = 1.875V
ILOAD = 50mA
Burst Mode OPERATION
VOUT
100mV/DIV
AC COUPLED
IL
500mA/DIV
ILOAD
500mA/DIV
35413 G21
VIN = 3.6V
40µs/DIV
VOUT = 1.8V
ILOAD = 1mA TO 500mA
VLDO Load Step from 1mA to
300mA
VOUT
100mV/DIV
AC COUPLED
IL
500mA/DIV
ILOAD
500mA/DIV
35413 G11
VIN = 3.6V
40µs/DIV
VOUT = 1.8V
ILOAD = 1mA TO 500mA
VLDO Load Step from 100mA to
300mA
35413 G12
LVOUT
20mV/DIV
AC COUPLED
ILOAD
250mA/DIV
VIN = 3.6V
400µs/DIV
VOUT = 1.575V
ILOAD = 1mA TO 300mA
35413 G13
LVOUT
20mV/DIV
AC COUPLED
ILOAD
250mA/DIV
VIN = 3.6V
400µs/DIV
VOUT = 1.575V
ILOAD = 100mA TO 300mA
35413 G14
35413fc
5 Page 
OPERATIOU
Transitioning from linear regulator mode to VLDO mode,
accomplished by bringing ENBUCK from a logic low to a
logic high while ENVLDO is a logic high or as occurs during
the auto start-up sequence, is designed to be as seam-
less and transient free as possible. The precise transient
response of LVOUT due to this transition is a function of
COUT and the load current. Waveforms given in the Typical
Performance Characteristics section show typical transient
responses using the minimum COUT of 2.2µF and load
currents of 1mA and 30mA respectively. Generally, the
wwwa.mDaptlaitSuhdeeeto4Uf .acnoymtransients present will decrease as COUT
is increased. To ensure reliable operation and adherence
to the load regulation limits presented in the Electrical
Characterstics table, the load current must not exceed
the linear regulator IOUT limit of 30mA within 20ms after
ENBUCK has transitioned to a logic high. The 300mA IOUT
limit of VLDO applies thereafter. Further, for configurations
that do not use the LTC3541-3’s buck regulator to provide
the VLDO input voltage (LVIN), the user must ensure a
stable LVIN voltage is present no less than 1ms prior to
ENBUCK transitioning to a logic high.
LTC3541-3
In a similar manner, transitioning from VLDO mode to
linear regulator mode, accomplished by bringing ENBUCK
from a high low to a logic low while ENVLDO is a logic
high, is designed to be as seamless and transient free as
possible. Again, the precise transient response of LVOUT
due to this transition is a function of COUT and the load
current. Waveforms given in the Typical Performance
Characteristics section show typical transient responses
using the minimum COUT of 2.2µF and load currents of
1mA and 30mA respectively. Generally, the amplitude of
any transients present will decrease as COUT is increased.
To ensure reliable operation and adherence to the load
regulation limits presented in the Electrical Characterstics
table, the load current must not exceed the linear regulator
IOUT limit of 30mA 1ms prior to ENBUCK transitioning to
a logic low and thereafer. Further, for configurations that
do not use the LTC3541-3’s buck regulator to provide the
VLDO input voltage (LVIN), the user must continue to ensure
a stable LVIN voltage no less than 1ms after ENBUCK has
transitioned to a logic low.
35413fc
11
11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet LTC3541-3.PDF ] | |
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