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PDF LTC3727A-1 Data sheet ( Hoja de datos )
| Número de pieza | LTC3727A-1 | |
| Descripción | 2-Phase Synchronous Step-Down Switching Regulators | |
| Fabricantes | Linear Technology | |
| 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% 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 36V 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 Package
U
APPLICATIO S
■ Telecom Systems
■ Automotive Systems
■ Battery-Operated Digital Devices
LTC3727A-1www.DataSheet4U.com
High Efficiency, 2-Phase
Synchronous Step-Down
Switching Regulators
DESCRIPTIO
The LTC®3727A-1 is a high performance dual step-down
switching regulator controller that drives all N-channel
synchronous power MOSFET stages. A constant fre-
quency 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.
The LTC3727A-1 is an improved version of the LTC3727
family of parts. It has smaller output ripple while in the
drop-out condition and shorter minimum on-time.
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 30V (36V maximum)
input supply range encompasses all battery chemistries.
A RUN/SS pin for each controller provides soft-start.
Current foldback limits MOSFET heat dissipation during
short-circuit conditions. Output overvoltage protection
circuitry protects the controller until VOUT returns to
normal.
, LTC and LT 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
BOOST2
SW1 SW2
LTC3727A-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
3727 F01
3727a1f
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
3727 G04
Maximum Current Sense Threshold
vs Duty Factor
150
125
100
75
50
25
0
0 20 40 60 80 100
DUTY FACTOR (%)
3727 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)
3727 G10
EXTVCC Voltage Drop
160
VEXTVCC = 8.5V
140
120
100
80
60
40
20
0
0 10 20 30
CURRENT (mA)
40 50
3727 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 (%)
3727 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
3727 G11
LTC3727A-1www.DataSheet4U.com
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 35
INPUT VOLTAGE (V)
3727 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)
3727 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
3727 G12
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U
OPERATIO (Refer to Functional Diagram)
Continuous Current (PWM) Operation
Tying the FCB pin to ground will force continuous current
operation. This is the least efficient operating mode, but
may be desirable in certain applications. The output can
source or sink current in this mode. When sinking current
while in forced continuous operation, current will be
forced back into the main power supply.
INTVCC/EXTVCC Power
Power for the top and bottom MOSFET drivers and most
other internal circuitry is derived from the INTVCC pin.
When the EXTVCC pin is left open, an internal 7.5V low
dropout linear regulator supplies INTVCC power. If EXTVCC
is taken above 7.3V, the 7.5V regulator is turned off and an
internal switch is turned on connecting EXTVCC to INTVCC.
This allows the INTVCC power to be derived from a high
efficiency external source such as the output of the regu-
lator itself or a secondary winding, as described in the
Applications Information section.
Output Overvoltage Protection
An overvoltage comparator, OV, guards against transient
overshoots (>7.5%) as well as other more serious condi-
tions that may overvoltage the output. In this case, the top
MOSFET is turned off and the bottom MOSFET is turned on
until the overvoltage condition is cleared.
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.
LTC3727A-1www.DataSheet4U.com
THEORY AND BENEFITS OF 2-PHASE OPERATION
The LTC3727A-1 dual high efficiency DC/DC controller
brings the considerable benefits of 2-phase operation to
portable applications. Notebook computers, PDAs,
handheld terminals and automotive electronics will all
benefit from the lower input filtering requirement, reduced
electromagnetic interference (EMI) and increased effi-
ciency associated with 2-phase operation.
Traditionally, constant-frequency dual switching regula-
tors operated both channels in phase (i.e., single-phase
operation). This means that both switches turned 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 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
LTC3727A-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
3727a1f
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| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet LTC3727A-1.PDF ] | |
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