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PDF LTC3727LX-1 Data sheet ( Hoja de datos )
| Número de pieza | LTC3727LX-1 | |
| Descripción | 2-Phase Synchronous Step-Down Switching Regulator | |
| Fabricantes | Linear | |
| Logotipo |  |
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FEATURES
■ Wide Output Voltage Range: 0.8V ≤ VOUT ≤ 14V
■ Out-of-Phase Controllers Reduce Required Input
Capacitance and Power Supply Induced Noise
■ OPTI-LOOP® Compensation Minimizes COUT
■ ±1.5% Output Voltage Accuracy
■ Power Good Output Voltage Monitor
■ Phase-Lockable Fixed Frequency 250kHz to 550kHz
■ Dual N-Channel MOSFET Synchronous Drive
■ Wide VIN Range: 4V to 32V Operation
■ Very Low Dropout Operation: 99% Duty Cycle
■ Adjustable Soft-Start Current Ramping
■ Foldback Output Current Limiting
■ Output Overvoltage Protection
■ Low Shutdown IQ: 20µA
■ Selectable Constant-Frequency or Burst Mode®
Operation
■ Small 28-Lead SSOP and 5mm × 5mm QFN Packages
U
APPLICATIO S
■ Telecom Systems
■ Automotive Systems
■ Distributed DC Power Systems
LTC3727LX-1
High Efficiency, 2-Phase
Synchronous Step-Down
Switching Regulator
DESCRIPTIO
The LTC®3727LX-1 is a high performance dual step-down
switching regulator controller that drives all N-channel
synchronous power MOSFET stages. A constant-frequency
current mode architecture allows phase-lockable frequency
of up to 550kHz. Power loss and noise due to the ESR of
the input capacitors are minimized by operating the two
controller output stages out of phase.
OPTI-LOOP compensation allows the transient response
to be optimized over a wide range of output capacitance and
ESR values. There is a precision 0.8V reference and a power
good output indicator. A wide 4V to 28V (32V maximum)
input supply range encompasses all battery chemistries.
Table 1
PART
NUMBER
VIN VREF ACCURACY LATCH-
RANGE OVERTEMPERATURE OFF
LTC3727LX-1 4V to 32V
±1.5%
No
LTC3727 4V to 36V
±1%
Yes
LTC3727-1 4V to 36V
±1%
No
LTC3727A-1 4V to 36V
±1%
No
MINIMUM
ON-TIME
120ns
180ns
180ns
120ns
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. Burst
Mode and OPTI-LOOP are registered trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners. Protected by U.S. Patents, including
5481178, 5929620, 6177787, 6144194, 6100678, 5408150, 6580258, 6304066, 5705919.
TYPICAL APPLICATIO
8µH
0.015Ω
VOUT1
5V
5A
+
47µF
6V
SP
105k
1%
+
4.7µF
M1
0.1µF
M2
1000pF
220pF
20k
1% 15k
VIN PGOOD INTVCC
TG1 TG2
BOOST1
SW1
BOOST2
SW2
LTC3727LX-1
BG1 BG2
PLLIN
SENSE1+
PGND
SENSE2+
SENSE1–
SENSE2–
VOSENSE1
VOSENSE2
ITH1 ITH2
RUN/SS1 SGND RUN/SS2
0.1µF
0.1µF
1µF
CERAMIC
0.1µF
M3
M4
VIN
22µF 18V TO 28V
50V
CERAMIC
15µH
1000pF
220pF
15k
280k
1%
20k
1%
0.015Ω
VOUT2
12V
4A
+ 56µF
15V
SP
M1, M2, M3, M4: FDS6680A
Figure 1. High Efficiency Dual 12V/5V Step-Down Converter
3727LX1 F01
3727lx1fa
1
1 page  
TYPICAL PERFOR A CE CHARACTERISTICS
Supply Current vs Input Voltage
and Mode (Figure 13)
1000
800
BOTH
CONTROLLERS ON
600
400
200
0
0
SHUTDOWN
10 20
INPUT VOLTAGE (V)
30 32
3727LX1 G04
Maximum Current Sense Threshold
vs Duty Factor
150
125
100
75
50
25
0
0 20 40 60 80 100
DUTY FACTOR (%)
3727LX1 G07
Current Sense Threshold
vs ITH Voltage
150
125
100
75
50
25
0
–25
–50
0
0.5 1.0 1.5 2.0 2.5
VITH (V)
3727LX1 G10
EXTVCC Voltage Drop
160
VEXTVCC = 8.5V
140
120
100
80
60
40
20
0
0 10 20 30
CURRENT (mA)
40 50
3727LX1 G05
Maximum Current Sense Threshold
vs Percent of Nominal Output
Voltage (Foldback)
150
135
120
105
90
75
60
45
30
15
0
0 20 40 60 80 100
PERCENT OF NOMINAL OUTPUT VOLTAGE (%)
3727LX1 G08
Load Regulation
0.0
–0.1
FCB = 0V
VIN = 15V
FIGURE 1
–0.2
–0.3
–0.4
0
1 2 34
LOAD CURRENT (A)
5
3727LX1 G11
LTC3727LX-1
Internal 7.5V LDO Line Regulation
7.7
ILOAD = 1mA
7.6
7.5
7.4
7.3
7.2
7.1
7.0
6.9
6.8
0 5 10 15 20 25 30 32
INPUT VOLTAGE (V)
3727LX1 G06
Maximum Current Sense Threshold
vs VRUN/SS (Soft-Start)
150
VSENSE(CM) = 1.6V
125
100
75
50
01 2 34 5 6
VRUN/SS (V)
3727LX1 G09
VITH vs VRUN/SS
2.5
VOSENSE = 0.7V
2.0
1.5
1.0
0.5
0
012 34
VRUN/SS (V)
56
3727LX1 G12
3727lx1fa
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5 Page 
U
OPERATIO (Refer to Functional Diagram)
Power Good (PGOOD) Pin
The PGOOD pin is connected to an open drain of an
internal MOSFET. The MOSFET turns on and pulls the
pin low when either output is not within ±7.5% of the
nominal output level as determined by the resistive
feedback divider. When both outputs meet the ±7.5%
requirement, the MOSFET is turned off within 10µs and
the pin is allowed to be pulled up by an external resistor
to a source of up to 7V.
THEORY AND BENEFITS OF 2-PHASE OPERATION
The LTC3727LX-1 dual high efficiency DC/DC controller
brings the considerable benefits of 2-phase operation to
portable applications. Notebook computers, PDAs, hand-
held terminals and automotive electronics will all benefit
from the lower input filtering requirement, reduced elec-
tromagnetic interference (EMI) and increased efficiency
associated with 2-phase operation.
When constant-frequency dual switching regulators oper-
ate both channels in phase (i.e., single-phase operation),
both switches turn on at the same time, causing current
pulses of up to twice the amplitude of those for one
regulator to be drawn from the input capacitor and battery.
These large amplitude current pulses increased the total
RMS current flowing from the input capacitor, requiring
LTC3727LX-1
the use of more expensive input capacitors and increasing
both EMI and losses in the input capacitor and battery.
With 2-phase operation, the two channels of the dual-
switching regulator are operated 180 degrees out of
phase. This effectively interleaves the current pulses
drawn by the switches, greatly reducing the overlap time
where they add together. The result is a significant reduc-
tion in total RMS input current, which in turn allows less
expensive input capacitors to be used, reduces shielding
requirements for EMI and improves real world operating
efficiency.
Figure 3 compares the input waveforms for a representa-
tive single-phase dual switching regulator to the new
LTC3727LX-1 2-phase dual switching regulator. An actual
measurement of the RMS input current under these con-
ditions shows that 2-phase operation dropped the input
current from 2.53ARMS to 1.55ARMS. While this is an
impressive reduction in itself, remember that the power
losses are proportional to IRMS2, meaning that the actual
power wasted is reduced by a factor of 2.66. The reduced
input ripple voltage also means less power is lost in the
input power path, which could include batteries, switches,
trace/connector resistances and protection circuitry. Im-
provements in both conducted and radiated EMI also
directly accrue as a result of the reduced RMS input
current and voltage.
5V SWITCH
20V/DIV
3.3V SWITCH
20V/DIV
INPUT CURRENT
5A/DIV
INPUT VOLTAGE
500mV/DIV
IIN(MEAS) = 2.53ARMS
(a)
3727LX1 F03a
IIN(MEAS) = 1.55ARMS
(b)
3727LX1 F03b
Figure 3. Input Waveforms Comparing Single-Phase (a) and 2-Phase (b) Operation for
Dual Switching Regulators Converting 12V to 5V and 3.3V at 3A Each. The Reduced Input
Ripple with the LTC3727LX-1 2-Phase Regulator Allows Less Expensive Input Capacitors,
Reduces Shielding Requirements for EMI and Improves Efficiency
3727lx1fa
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11 Page | ||
| Páginas | Total 28 Páginas | |
| PDF Descargar | [ Datasheet LTC3727LX-1.PDF ] | |
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