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PDF LTC3614 Data sheet ( Hoja de datos )
| Número de pieza | LTC3614 | |
| Descripción | 4MHz Monolithic Synchronous Step-Down DC/DC Converter | |
| Fabricantes | Linear | |
| Logotipo |  |
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Features
n 4A Output Current
n 2.25V to 5.5V Input Voltage Range
n Low Output Ripple Burst Mode® Operation: IQ = 75µA
n ±1% Output Voltage Accuracy
n Output Voltage Down to 0.6V
n High Efficiency: Up to 95%
n Low Dropout Operation: 100% Duty Cycle
n Programmable Slew Rate on SW Node Reduces
Noise and EMI
n Adjustable Switching Frequency: Up to 4MHz
n Optional Active Voltage Positioning (AVP) with
Internal Compensation
n Selectable Pulse-Skipping/Forced Continuous/Burst
Mode Operation with Adjustable Burst Clamp
n Programmable Soft-Start
n Inputs for Start-Up Tracking or External Reference
n DDR Memory Mode, IOUT = ±3A
n Available in a 24-Pin 3mm × 5mm QFN
Thermally Enhanced Package
Applications
n Point-of-Load Supplies
n Distributed Power Supplies
n Portable Computer Systems
n DDR Memory Termination
n Handheld Devices
LTC3614
4A, 4MHz Monolithic
Synchronous Step-Down
DC/DC Converter
Description
The LTC®3614 is a low quiescent current monolithic syn-
chronous buck regulator using a current mode, constant
frequency architecture. The no-load DC supply current
in sleep mode is only 75µA while maintaining the output
voltage (Burst Mode operation) at no load, dropping to
zero current in shutdown. The 2.25V to 5.5V input supply
voltage range makes the LTC3614 ideally suited for single
Li-Ion as well as fixed low voltage input applications. 100%
duty cycle capability provides low dropout operation,
extending the operating time in battery-powered systems.
The operating frequency is externally programmable up to
4MHz, allowing the use of small surface mount inductors.
For switching-noise-sensitive applications, the LTC3614
can be synchronized to an external clock at up to 4MHz.
Forced continuous mode operation in the LTC3614 reduces
noise and RF interference. Adjustable compensation allows
the transient response to be optimized over a wide range
of loads and output capacitors.
The internal synchronous switch increases efficiency and
eliminates the need for an external catch diode, saving
external components and board space. The LTC3614
is offered in a leadless 24-pin 3mm × 5mm thermally
enhanced QFN package.
L, LT, LTC, LTM, Linear Technology, the Linear logo 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, 5994885, 6304066, 6498466, 6611131.
Typical Application
VIN
2.7V TO 5.5V
SVIN
PVIN
RUN SRLIM/DDR
TRACK/SS
RT/SYNC
LTC3614
SW
PGOOD
SGND
ITH PGND
MODE
VFB
210k
10µF
×4
330nH
665k
VOUT
2.5V
4A
47µF
×2
3614 TA01a
Efficiency and Power Loss
vs Load Current
100
90
80 1
70
60 0.1
50
40 0.01
30
20
10
0 VOUT = 2.5V
1 10
VIN = 2.8V
VIN = 3.3V
VIN = 5V
0
100 1000 10000
OUTPUT CURRENT (mA)
3614 TA01b
For more information www.linear.com/LTC3614
3614fc
1
1 page  
LTC3614
Typical Performance Characteristics VIN = 3.3V, RT/SYNC = SVIN unless otherwise noted.
Efficiency vs Load Current
Burst Mode Operation (VMODE = 0V)
100 VOUT = 1.8V
90
80
70
60
50
40
30
20 VIN = 2.5V
10 VIN = 3.3V
0 VIN = 5V
1 10 100 1000 10000
OUTPUT CURRENT (mA)
3614 G01
Efficiency vs Input Voltage
Burst Mode Operation
(VMODE = 0V)
100 VOUT = 1.8V
90
80
70
60
50
40
30
2.5
IOUT = 6mA
IOUT = 600mA
IOUT = 2A
3 3.5 4 4.5 5 5.5
INPUT VOLTAGE (V)
3614 G04
Efficiency vs Load Current
Burst Mode Operation (VMODE = 0V)
100
90
VOUT = 1.2V
80
70
60
50
40
30
20 VIN = 2.5V
10 VIN = 3.3V
0 VIN = 5V
1 10 100 1000 10000
OUTPUT CURRENT (mA)
3614 G02
Efficiency vs Frequency
Burst Mode Operation
(VMODE = 0V), IOUT = 2A
95
94
93
VIN = 3.3V
VOUT = 1.8V
92
91
90
89
88
87
86
85
84
83
150nH
330nH
470nH
82
0.5 1 1.5 2 2.5 3 3.5 4 4.5
FREQUENCY (MHz)
3614 G05
Efficiency vs Load Current
100 VOUT = 1.8V
90
80
70
60
50
40
30
20 Burst Mode OPERATION
10 PULSE-SKIPPING
0 FORCED CONTINUOUS
1 10 100 1000 10000
OUTPUT CURRENT (mA)
3614 G03
Load Regulation
(VOUT = 1.8V)
1.5 FORCED CONTINUOUS MODE
1.3 PULSE-SKIPPING MODE
INTERNAL Burst Mode OPERATION
1.1
0.9
0.7
0.5
0.3
0.1
–0.1
–0.3
0
1000
2000
3000
OUTPUT CURRENT (mA)
4000
3614 G06
Line Regulation
0.3
Burst Mode Operation
Pulse-Skipping Mode Operation
0.2
0.1
VOUT
20mV/DIV
VOUT
20mV/DIV
0
–0.1
–0.2
–0.3
2.20 2.75
3.30 3.85 4.40
INPUT VOLTAGE (V)
4.95 5.50
3614 G07
IL
1A/DIV
VOUT = 1.8V
IOUT = 150mA
VMODE = 0V
20µs/DIV
3614 G08
IL
1A/DIV
VOUT = 1.8V
IOUT = 150mA
VMODE = 3.3V
20µs/DIV
3614 G09
For more information www.linear.com/LTC3614
3614fc
5
5 Page 
LTC3614
Operation
Main Control Loop
The LTC3614 is a monolithic, constant frequency, current
mode step-down DC/DC converter. During normal opera-
tion, the internal top power switch (P-channel MOSFET) is
turned on at the beginning of each clock cycle. Current in
the inductor increases until the current comparator trips
and turns off the top power switch. The peak inductor cur-
rent at which the current comparator trips is controlled by
the voltage on the ITH pin. The error amplifier adjusts the
voltage on the ITH pin by comparing the feedback signal
from a resistor divider on the VFB pin with an internal 0.6V
reference. When the load current increases, it causes a
reduction in the feedback voltage relative to the reference.
The error amplifier raises the ITH voltage until the average
inductor current matches the new load current. Typical
voltage range for the ITH pin is from 0.1V to 0.8V with
0.45V corresponding to zero current.
When the top power switch shuts off, the synchronous
power switch (N-channel MOSFET) turns on until either
the bottom current limit is reached or the next clock cycle
begins. The bottom current limit is typically set at –8A for
forced continuous mode and 0A for Burst Mode operation
and pulse-skipping mode.
The operating frequency defaults to 2.25MHz when
RT/SYNC is connected to SVIN, or can be set by an ex-
ternal resistor connected between the RT/SYNC pin and
ground, or by a clock signal applied to the RT/SYNC pin.
The switching frequency can be set from 300kHz to 4MHz.
Overvoltage and undervoltage comparators pull the
PGOOD output low if the output voltage varies more than
±7.5% (typical) from the set point.
Mode Selection
The MODE pin is used to select one of four different
operating modes:
Mode Selection Voltage
SVIN
SVIN – 0.3V
SVIN • 0.58
PS PULSE-SKIPPING MODE ENABLE
FC FORCED CONTINUOUS MODE ENABLE
1.1V
0.8V
0.45V
0.3V
SGND
BM
EXT
Burst Mode ENABLE—EXTERNAL CLAMP,
CONTROLLED BY VOLTAGE APPLIED AT
MODE PIN
BM Burst Mode ENABLE—INTERNAL CLAMP
3614 OP01
Burst Mode Operation—Internal Clamp
Connecting the MODE pin to SGND enables Burst Mode
operation with an internal clamp. In Burst Mode operation
the internal power switches operate intermittently at light
loads. This increases efficiency by minimizing switching
losses. During the intervals when the switches are idle,
the LTC3614 enters sleep state where many of the internal
circuits are disabled to save power. During Burst Mode
operation, the minimum peak inductor current is internally
clamped and the voltage on the ITH pin is monitored by
the burst comparator to determine when sleep mode is
enabled and disabled. When the average inductor current
is greater than the load current, the voltage on the ITH pin
drops. As the ITH voltage falls below the internal clamp,
the burst comparator trips and enables sleep mode. Dur-
ing sleep mode, both power MOSFETs are held off and
the load current is solely supplied by the output capacitor.
When the output voltage drops, the top power switch is
turned back on and the internal circuits are re-enabled.
This process repeats at a rate that is dependent on the
load current.
For more information www.linear.com/LTC3614
3614fc
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11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet LTC3614.PDF ] | |
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