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PDF LTC3874 Data sheet ( Hoja de datos )
| Número de pieza | LTC3874 | |
| Descripción | PolyPhase Step-Down Synchronous Slave Controller | |
| Fabricantes | Linear | |
| Logotipo |  |
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LTC3874
PolyPhase Step-Down
Synchronous Slave Controller with
Sub-Milliohm DCR Sensing
FEATURES
n Phase Extender for High Phase Count Voltage Rails
n Accurate Phase-to-Phase Current Sharing
n Sub-Milliohm DCR Current Sensing
n Phase-Lockable Fixed Frequency 250kHz to 1MHz
n Immediate Response to Master IC's Fault
n Up to 12 Phase Operation
n Wide VIN Range: 4.5V to 38V
n VOUT Up to 5.5V
n Proprietary Current Mode Control Loop
n Programmable CCM/DCM Operation
n Programmable Phase Shift Control
n Dual N-Channel MOSFET Gate Drivers
n 28-Lead (4mm × 5mm) QFN Package
APPLICATIONS
n High Current Distributed Power Systems
n Telecom, Datacom, and Storage Systems
n Intelligent Energy Efficient Power Regulation
DESCRIPTION
The LTC®3874 is a dual PolyPhase® current mode synchro-
nous step-down slave controller. It enables high current,
multi-phase applications when paired with a companion
master controller by extending the phase count. Compat-
ible master controllers include the LTC3866, LTC3875 and
LTC3774. The LTC3874 employs a unique architecture that
enhances the signal-to-noise ratio of the current sense
signal, allowing the use of sub-milliohm DC resistance
power inductors to maximize efficiency while reduc-
ing switching jitter. Its peak current mode architecture
allows for accurate phase to phase current sharing even
for dynamic loads.
Effectively working with a master controller, the LTC3874
supports all the programmable features as well as fault
protection. The constant operating frequency can be
synchronized to an external clock or linearly programmed
from 250KHz to 1MHz.
L, LT, LTC, LTM, Linear Technology, the Linear logo, PolyPhase 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 5481178, 5705919, 5929620, 6100678,
6144194, 6177787, 6304066, 6580258.
TYPICAL APPLICATION
VIN
4.7µF
90k
VIN INTVCC
LTC3874 TG0
PHASMD BOOST0
LOWDCR SW0
EXTVCC
BG0
FREQ
ILIM
ISENSE0+
ISENSE0–
MASTER
RUN0
CONTROLLER RUN1
GPIO0
VSENSE0+
VSENSE1+
GPIO1
PGOOD0
PGOOD1
ITH0
ITH1
SYNC
RUN0
RUN1
FAULT0
FAULT1
MODE0
MODE1
ITH0
ITH1
SYNC
TG1
BOOST1
SW1
BG1
GND
ISENSE1+
ISENSE1–
0.1µF
931Ω
0.22µF
0.1µF
931Ω
0.22µF
0.33µH
(0.32mΩ DCR)
+ 470µF
×2
VOUT
1.8V
120A
0.33µH
(0.32mΩ DCR)
+ 470µF
×2
3874 TA02
For more information www.linear.com/LTC3874
Dual Phase Efficiency and Power Loss
vs Output Current, Sub-Milliohm DCR
vs Traditional DCR
100 VIN = 12V
VOUT = 1.8V
95 CCM
14
12
90
85
80
75
70
0
EFFICIENCY
10
8
POWER LOSS
6
0.32mΩ 4
1.5mΩ
0.32mΩ
2
1.5mΩ
0
10 20 30 40 50 60
LOAD CURRENT (A)
3874 TA01b
3874f
1
1 page  
LTC3874
TYPICAL PERFORMANCE CHARACTERISTICS (TA = 25°C unless otherwise specified)
Efficiency vs Output Current
and Mode
100
90
80
70
DCM
60
50
40
CCM
VIN = 12V
VOUT = 1.2V
30
20
10
0
0.1 1 10 100
LOAD CURRENT (A)
3874 G01
Efficiency vs Output Current
and Mode
100
90
80 DCM
70
60
50 CCM
40
VIN = 12V
VOUT = 1.8V
30
20
10
0
0.1 1 10 100
LOAD CURRENT (A)
3874 G02
Dual Phase Efficiency and Power
Loss vs Output Current
100 VIN = 12V
VOUT = 1.8V
95 CCM
14
12
90
85
80
75
70
0
EFFICIENCY
10
8
POWER LOSS
6
0.32mΩ 4
1.5mΩ
0.32mΩ
2
1.5mΩ
0
10 20 30 40 50 60
LOAD CURRENT (A)
3874 G03
Load Step (Forced Continuous
Mode) 3-Phase with Master
Controller LTC3866
Load Step (Discontinuous
Conduction Mode) 3-Phase with
Master Controller LTC3866
IL(MASTER)
20A/DIV
IL(SLAVE1)
20A/DIV
IL(SLAVE0)
20A/DIV
VOUT
200mV/DIV
AC-COUPLED
VIN = 12V
VOUT = 1.2V
ILOAD 5A TO 50A
50µs/DIV
3874 G04
IL(MASTER)
20A/DIV
IL(SLAVE1)
20A/DIV
IL(SLAVE0)
20A/DIV
VOUT
200mV/DIV
AC-Coupled
VIN = 12V
VOUT = 1.2V
ILOAD 5A TO 50A
50µs/DIV
3874 G05
Inductor Current at Light Load
FORCED
CONTINUOUS
MODE
5A/DIV
DISCONTINUOUS
CONDUCTION
MODE
5A/DIV
VIN = 12V
VOUT = 1.2V
ILOAD = 2A
1µs/DIV
3874 G06
Start-Up Into a Pre-Biased Output
with Master Controller LTC3875
RUN
5V/DIV
OV
VOUT
1V/DIV
OV
VIN = 12V
VOUT = 1.0V
20ms/DIV
3874 G06a
For more information www.linear.com/LTC3874
3874f
5
5 Page 
OPERATION
3 PHASE OPERATION
0°
LTC3866
CLKOUT
CH0
240°
CH1
120°
LTC3874
SYNC
PHASMD = 1/3 INTVCC
LTC3874
4 PHASE OPERATION
6 PHASE OPERATION
CH1 CH2
0° 180°
LTC3875
CLKOUT
CH0 CH1
90° 270°
LTC3874
SYNC
CH1 CH2
0° 240°
LTC3875
CLKOUT
CH0 CH1
120° 300°
LTC3874
SYNC
CH0 CH1
60° 180°
LTC3874
SYNC
PHASMD = FLOAT
PHASMD = GND
PHASMD = INTVCC
PHASMD = GND
Figure 1. Multiphase Operation
PHASMD = 2/3 INTVCC
3874 F01
Frequency Selection and Phase-Locked Loop
(FREQ and SYNC Pins)
The selection of switching frequency is a trade-off between
efficiency and component size. Low frequency operation
increases efficiency by reducing MOSFET switching losses,
but requires larger inductance and/or capacitance to main-
tain low output ripple voltage. The switching frequency of
the LTC3874 controllers can be selected using the FREQ
pin. If the SYNC pin is not being driven by an external clock
source, the FREQ pin can be used to program the control-
ler’s operating frequency from 250kHz to 1MHz. There is a
precision 10µA current flowing out of the FREQ pin, so the
user can program the controller’s switching frequency with
a single resistor to GND. A curve is provided later in the
application section showing the relationship between the
voltage on the FREQ pin and switching frequency (Figure
5). A phase-locked loop (PLL) is integrated in the LTC3874
to synchronize the internal oscillator to an external clock
source on the SYNC pin. The PLL loop filter network is
integrated inside the LTC3874. The phase-locked loop is
capable of locking to any frequency within the range of
250kHz to 1MHz. The frequency setting resistor should
always be present to set the controller’s initial switching
frequency before locking to the external clock.
For more information www.linear.com/LTC3874
3874f
11
11 Page | ||
| Páginas | Total 28 Páginas | |
| PDF Descargar | [ Datasheet LTC3874.PDF ] | |
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