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PDF LTC3780 Data sheet ( Hoja de datos )
| Número de pieza | LTC3780 | |
| Descripción | 4-Switch Buck-Boost Controller | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LTC3780 (archivo pdf) en la parte inferior de esta página. Total 28 Páginas | ||
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LTC3780
FEATURES
■ Single Inductor Architecture Allows VIN Above,
Below or Equal to VOUT
■ Wide VIN Range: 4V to 36V Operation
■ Synchronous Rectification: Up to 98% Efficiency
■ Current Mode Control
■ ±1% Output Voltage Accuracy: 0.8V < VOUT < 30V
■ Phase-Lockable Fixed Frequency: 200kHz to 400kHz
■ Power Good Output Voltage Monitor
■ Internal LDO for MOSFET Supply
■ Quad N-Channel MOSFET Synchronous Drive
■ VOUT Disconnected from VIN During Shutdown
■ Adjustable Soft-Start Current Ramping
■ Foldback Output Current Limiting
■ Selectable Low Current Modes
■ Output Overvoltage Protection
■ Available in 24-Lead SSOP and Exposed Pad
(5mm × 5mm) 32-Lead QFN Packages
U
APPLICATIO S
■ Automotive Systems
■ Telecom Systems
■ DC Power Distribution Systems
■ High Power Battery-Operated Devices
www■.DaItnaSdhuesettr4iUa.lcComontrol
High Efficiency, Synchronous,
4-Switch Buck-Boost Controller
DESCRIPTIO
The LTC®3780 is a high performance buck-boost switch-
ing regulator controller that operates from input voltages
above, below or equal to the output voltage. The constant
frequency current mode architecture allows a phase-
lockable frequency of up to 400kHz. With a wide 4V to 30V
(36V maximum) input and output range and seamless
transfers between operating modes, the LTC3780 is ideal
for automotive, telecom and battery-powered systems.
The operating mode of the controller is determined through
the FCB pin. For boost operation, the FCB mode pin can
select among Burst Mode® operation, Discontinuous mode
and Forced Continuous mode. During buck operation, the
FCB mode pin can select among Skip-Cycle mode, Discon-
tinuous mode and Forced Continuous mode. Burst Mode
operation and Skip-Cycle mode provide high efficiency
operation at light loads while Forced Continuous mode
and Discontinuous mode operate at a constant frequency.
Fault protection is provided by an output overvoltage
comparator and internal foldback current limiting. A Power
Good output pin indicates when the output is within 7.5%
of its designed set point.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Protected by U.S. Patents, including 5481178, 6304066, 5929620, 5408150, 6580258,
patent pending on current mode architecture and protection
TYPICAL APPLICATIO
High Efficiency Buck-Boost Converter
VIN
4V TO 36V
22µF
50V
CER
+
4.7µF
0.1µF
VIN PGOOD INTVCC
TG2 TG1
BOOST2 BOOST1
2200pF
20k
SW2 SW1
LTC3780
BG2 BG1
ITH
SS
0.1µF
PLLIN
RUN
VOSENSE
SGND
FCB
SENSE+ SENSE– PGND
1µF
CER
0.1µF
ON/OFF
105k
1%
7.5k
1000pF
0.010Ω
2µH
100µF
16V
CER
VOUT
12V
5A
3780 TA01
Efficiency and Power Loss
VOUT = 12V, ILOAD = 5A
100 10
9
95 8
90 7
6
85 5
4
80 3
75 2
1
70
05
0
10 15 20 25 30 35
VIN (V)
3780 TA01b
3780f
1
1 page  
LTC3780
TYPICAL PERFOR A CE CHARACTERISTICS TA = 25°C unless otherwise noted.
Efficiency vs Output Current
(Boost Operation)
100
BURST
90
DCM
80
70
CCM
60
50
40
0.01
VIN = 6V
VOUT = 12V
0.1 1
ILOAD (A)
10
3780 G01
Supply Current vs Input Voltage
2500
2000
VFCB = 0V
1500
STANDBY
1000
500
SHUTDOWN
0
www.DataS0heet45U.co1m0 15 20 25
INPUT VOLTAGE (V)
30 35
3780 G04
INTVCC and EXTVCC Switch
Voltage vs Temperature
6.05
6.00
INTVCC VOLTAGE
5.95
5.90
5.85
5.80
5.75
5.70
5.65 EXTVCC SWITCHOVER THRESHOLD
5.60
5.55
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3780 G07
Efficiency vs Output Current
100
BURST
90
80
DCM
CCM
70
60
50
40
0.01
VIN = 12V
VOUT = 12V
0.1 1
ILOAD (A)
10
3780 G02
Internal 6V LDO Line Regulation
6.5
6.0
5.5
5.0
4.5
4.0
3.5
05
10 15 20 25 30 35
INPUT VOLTAGE (V)
3780 G05
EXTVCC Switch Resistance
vs Temperature
5
4
3
2
1
0
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3780 G08
Efficiency vs Output Current
(Buck Operation)
100
90
SC
80
CCM
70
DCM
60
50
40
0.01
VIN = 18V
VOUT = 12V
0.1 1
ILOAD (A)
10
3780 G03
EXTVCC Voltage Drop
120
100
80
60
40
20
0
1 10 20 30 40
CURRENT (mA)
50
3780 G06
Load Regulation
0
–0.1
VIN = 18V
–0.2
VIN = 12V
–0.3
VIN = 6V
–0.4
FCB = 0V
VOUT = 12V
–0.5
01 2 34
LOAD CURRENT (A)
5
3780 G09
3780f
5
5 Page 
U
OPERATIO
MAIN CONTROL LOOP
The LTC3780 is a current mode controller that provides an
output voltage above, equal to or below the input voltage.
The LTC proprietary topology and control architecture
employs a current-sensing resistor in Buck or Boost modes.
The sensed inductor current is controlled by the voltage on
the ITH pin, which is the output of the amplifier EA. The
VOSENSE pin receives the voltage feedback signal, which is
compared to the internal reference voltage by the EA.
The top MOSFET drivers are biased from floating booststrap
capacitors CA and CB (Figure 11), which are normally
recharged through an external diode when the top MOSFET
is turned off. Schottky diodes across the synchronous
switch D and synchronous switch B are not required, but
provide a lower drop during the dead time. The addition of
the Schottky diodes will typically improve peak efficiency
by 1% to 2% at 400kHz.
The main control loop is shut down by pulling the RUN pin
low. When the RUN pin voltage is higher than 1.5V, an
internal 1.2µA current source charges soft-start capacitor
CSS at the SS pin. The ITH voltage is then clamped to the
LTC3780
SS voltage while CSS is slowly charged during start-up.
This “soft-start” clamping prevents abrupt current from
being drawn from the input power supply.
POWER SWITCH CONTROL
Figure 1 shows a simplified diagram of how the four power
switches are connected to the inductor, VIN, VOUT and
GND. Figure 2 shows the regions of operation for the
LTC3780 as a function of duty cycle D. The power switches
are properly controlled so the transfer between modes is
continuous. When VIN approaches VOUT, the Buck-Boost
region is reached; the mode-to-mode transition time is
typically 200ns.
Buck Region (VIN > VOUT)
Switch D is always on and Switch C is always off during
this mode. At the start of every cycle, Synchronous Switch
B is turned on first. Inductor current is sensed when
Synchronous Switch B is turned on. After the sensed
inductor current falls below the reference voltage, which is
proportional to VITH, Synchronous Switch B is turned off
www.DataSheet4U.com
VIN VOUT
TG2 A
D TG1
SW2 L SW1
BG2 B
C BG1
RSENSE
3780 F01
Figure 1. Simplified Diagram of the Output Switches
98%
DMAX
BOOST
DMIN
BOOST
DMAX
BUCK
3%
DMIN
BUCK
A ON, B OFF
PWM C, D SWITCHES
BOOST REGION
FOUR SWITCH PWM BUCK/BOOST REGION
D ON, C OFF
PWM A, B SWITCHES
BUCK REGION
3780 F02
Figure 2. Operating Mode vs Duty Cycle
3780f
11
11 Page | ||
| Páginas | Total 28 Páginas | |
| PDF Descargar | [ Datasheet LTC3780.PDF ] | |
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