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PDF LTC3545-1 Data sheet ( Hoja de datos )
| Número de pieza | LTC3545-1 | |
| Descripción | Triple 800mA Synchronous Step-Down Regulator-2.25MHz | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC3545/LTC3545-1
Triple 800mA Synchronous
Step-Down Regulator–2.25MHz
FEATURES
DESCRIPTION
■ Three 800mA Outputs
■ High Efficiency: Up to 95%
■ 2.25V to 5.5V Input Voltage Range
■ Low Ripple (<20mVP-P) Burst Mode® Operation
IQ: 58μA
■ 2.25MHz Constant Frequency Operation or
■ Synchronizable to External 1MHz to 3MHz Clock
www■.DaPtoawSheereGt4oUo.cdomIndicators Ease Supply Sequencing
■ 0.6V Reference Allows Low Output Voltages
■ Current Mode Operation/Excellent Transient Response
■ Low Profile 16-Lead 3mm × 3mm QFN Package
APPLICATIONS
■ Smart Phones
■ Wireless and DSL Modems
■ Digital Still Cameras
■ Portable Instruments
■ Point of Load Regulation
L, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Protected by U.S. Patents including 6580258, 5481178, 6127815, 6498466, 6611131.
The LTC®3545/LTC3545-1 are triple, high efficiency,
monolithic synchronous buck regulators using a constant
frequency, current mode architecture. The regulators op-
erate independently with separate run pins. The 2.25V to
5.5V input voltage range makes the LTC3545/LTC3545-1
well suited for single Li-Ion battery-powered applications.
Low ripple pulse skip mode or high efficiency Burst Mode
operation is externally selectable. PWM pulse skip mode
operation provides very low output ripple voltage while
Burst Mode operation increases efficiency at low output
loads.
Switching frequency is internally set to 2.25MHz, or the
switching frequency can be synchronized to an external
1MHz to 3MHz clock. Power good indicators easily allow
power on sequencing between the three regulators.
The internal synchronous switches increase efficiency and
eliminate external Schottky diodes. Low output voltages are
supported with the 0.6V feedback reference voltage.
The LTC3545-1 replaces the SYNC/MODE function with a
third PGOOD pin and forces Burst Mode operation.
TYPICAL APPLICATION
High Efficiency Triple Step-Down Converter with Power Sequencing
VOUT1
1.8V
C1
10μF
VIN
2.25V TO 5.5V
C4 10μF
C5
10μF
GNDA
R8 R7
500k 500k
RUN1
VIN PVIN
PGND
L2
1.5μH
SW2
PGOOD1
RUN2
PGOOD2
VFB2
R4
226k
RUN3 LTC3545
L1
1.5μH
C6
20pF
SYNC/MODE
SW1
L3
1.5μH
SW3
R1
511k
VFB1
R2 GNDA
255k
VFB3
PGND
R6
200k
C7
20pF
R3
226k
C8
20pF
R5
301k
VOUT2
1.2V
C2
10μF
VOUT3
1.5V
C3
10μF
3545 TA01
Efficiency and Loss vs Load Current
100 1
90
80
0.1
70
60
50 0.01
40
30
20
10
0
0.0001
0.001
0.001
0.01
VIN = 2.5V
VIN = 3.6V
VIN = 4.2V
0.0001
0.1 1
LOAD CURRENT (A)
TA = 25°C
VOUT = 2V
Burst Mode OPERATION
fOSC = 2.25MHz
SINGLE CHANNEL
3545 TA01b
35451fb
1
1 page  
LTC3545/LTC3545-1
TYPICAL PERFORMANCE CHARACTERISTICS
Supply Current vs Temperature,
Pulse Skipping
450
400
350
300
250
www.Da2t0a0ShVeFBe3t=4U0..6c2o5Vm
ILOAD = 0mA
CHANNEL 3 ONLY
150
–50 0
50
VIN = 5.5V
VIN = 4.5V
VIN = 3.5V
VIN = 2.5V
100 150
TEMPERATURE (°C)
3545 G07
Channel 1 Load Step Response
Efficiency vs Load Current,
Burst Mode Operation
100
90
80
70
60
50
40
VIN = 2.7V
VIN = 3.6V
30 VIN = 4.2V
20
TA = 25°C
VOUT = 1.8V
10 CHANNEL 3, OTHER CHANNELS OFF
fOSC = 2.25MHz
0
0.1 1 10 100
LOAD CURRENT (mA)
1000
3545 G08
Channel 2 Load Step Response
Efficiency vs Load Current,
Pulse Skipping Operation
100
90
80
70
60
50
40
30
20
10
0
0.1
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
TA = 25°C
VOUT = 1.8V
CHANNEL 3, OTHER CHANNELS OFF
fOSC = 2.25MHz
1 10 100
LOAD CURRENT (mA)
1000
3545 G09
Channel 3 Load Step Response
VOUT1
100mV/DIV
IL
500mA/DIV
ILOAD
500mA/DIV
TA = 25°C
10μs/DIV
VIN = 3.6V
VOUT = 1.2V
LOAD STEP 0mA TO 600mA
Burst Mode OPERATION
VOUT2
100mV/DIV
IL
500mA/DIV
ILOAD
500mA/DIV
3545 G10
TA = 25°C
10μs/DIV
VIN = 3.6V
VOUT = 1.5V
LOAD STEP 0mA TO 600mA
Burst Mode OPERATION
VOUT3
100mV/DIV
IL
500mA/DIV
ILOAD
500mA/DIV
3545 G11
TA = 25°C
10μs/DIV
VIN = 3.6V
VOUT = 1.8V
LOAD STEP 0mA TO 600mA
Burst Mode OPERATION
3545 G12
35451fb
5
5 Page 
LTC3545/LTC3545-1
OPERATION
SOFT-START
Soft-start reduces surge currents on VIN and output
overshoot during start-up. Soft-start on the LTC3545/
LTC3545-1 is implemented by internally ramping the refer-
ence signal fed to the error amplifier over approximately a
1ms period. Figure 1 shows the behavior of the regulator
channels during start-up.
Short-Circuit Protection
wwwS.Dhaotrat-Schierectu4iUt.pcroomtection is achieved by monitoring the in-
ductor current. When the current exceeds a predetermined
level, the main switch is turned off, and the synchronous
switch is turned on long enough to allow the current in the
inductor to decay below the fault threshold. This prevents
a catastrophic inductor current run-away condition, but
will still provide current to the output. Output voltage
regulation in this condition is not achieved.
DROPOUT OPERATION
As the input supply voltage decreases to a value approach-
ing the output voltage, the duty cycle increases toward the
maximum on-time. Further reduction of the supply voltage
forces the main switch to remain on for more than one
cycle until it reaches 100% duty cycle. The output volt-
age will then be determined by the input voltage minus
the voltage drop across the P-channel MOSFET and the
inductor. An important detail to remember is that at low
input supply voltages, the RDS(ON) of the P-channel switch
increases (see Typical Performance Characteristics).
Therefore, the user should calculate the power dissipation
when the LTC3545/LTC3545-1 is used at 100% duty cycle
with low input voltage (See Thermal Considerations in the
Applications Information section).
VOUT1
VOUT2
VOUT3
(ALL 1V/DIV)
RUNX
2V/DIV
TA = 25°C
200μs/DIV
VIN = 3.6V
ILOAD = 0mA, ALL CHANNELS
3545 F01
Figure 1. Start-Up from Shutdown, No Load
35451fb
11
11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet LTC3545-1.PDF ] | |
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