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PDF LTC3788-1 Data sheet ( Hoja de datos )
| Número de pieza | LTC3788-1 | |
| Descripción | Dual Output Synchronous Boost Controller | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC3788-1
2-Phase, Dual Output
Synchronous Boost Controller
FEATURES
DESCRIPTION
n Synchronous Operation for Highest Efficiency and
Reduced Heat Dissipation
n Wide Input Range: 4.5V to 38V (40V Abs Max) and
Operates Down to 2.5V After Start-Up
n Output Voltages Up to 60V
n ±1% 1.2V Reference Voltage
n RSENSE or Inductor DCR Current Sensing
n 100% Duty Cycle Capability for Synchronous MOSFET
n Low Quiescent Current: 125μA
n Phase-Lockable Frequency (75kHz to 850kHz)
n Programmable Fixed Frequency (50kHz to 900kHz)
n Adjustable Output Voltage Soft-Start
n Power Good Output Voltage Monitor
n Low Shutdown Current IQ: < 8μA
n Internal LDO Powers Gate Drive from VBIAS or EXTVCC
n Available in a Narrow SSOP Package
APPLICATIONS
n Industrial
n Automotive
n Medical
n Military
www.DataSheet4U.com
The LTC®3788-1 is a high performance 2-phase dual
synchronous boost converter controller that drives all
N-channel power MOSFETs. Synchronous rectification
increases efficiency, reduces power losses and eases
thermal requirements, allowing the LTC3788-1 to be used
in high power boost applications.
A constant-frequency current mode architecture allows
a phase-lockable frequency of up to 850kHz. OPTI-LOOP
compensation allows the transient response to be optimized
over a wide range of output capacitance and ESR values.
The LTC3788-1 features a precision 1.2V reference and a
power good output indicator. A 4.5V to 38V input supply
range encompasses a wide range of system architectures
and battery chemistries.
Independent SS pins for each controller ramp the output
voltages during start-up. The PLLIN/MODE pin selects
among Burst Mode operation, pulse-skipping mode or
continuous inductor current mode at light loads.
For a leadless 32-pin QFN package with additional features
of adjustable current limit, clock out, phase modulation
and two PGOOD outputs, see the LTC3788 data sheet.
L, LT, LTC, LTM, Linear Technology, OPTI-LOOP, Burst Mode and the Linear logo are registered
trademarks and No RSENSE and ThinSOT are trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners. Protected by U. S. Patents,
including 5408150, 5481178, 5705919, 5929620, 6144194, 6177787, 6580258.
TYPICAL APPLICATION
VIN 4.5V TO 12V START-UP VOLTAGE
OPERATES THROUGH TRANSIENTS DOWN TO 2.5V
VIN
VOUT
12V AT 5A
3mΩ
1.25μH
110k
220μF
12.1k
4.7μF
4.7μF
4mΩ
220μF
TG1 VBIAS INTVCC TG2
0.1μF
BOOST1
BOOST2
SW1 SW2
LTC3788-1
BG1 BG2
0.1μF
3.3μH
VOUT
24V AT 3A
SENSE1+
SENSE2+
SENSE1–
SENSE2–
RUN1
PGND
15nF
2.7k
VFB1
RUN2
PGOOD1
VFB2
FREQ
EXTVCC
PLLIN/MODE
ITH1 SS1 SGND SS2 ITH2
100pF
0.1μF
0.1μF
232k
15nF
220pF 8.66k 12.1k
220μF
37881 TA01a
Efficiency and Power Loss
vs Load Current
100 10000
90
80 1000
70
60 100
50
40 10
30
20
10
0
0.00001 0.0001 0.001
VIN = 12V
1
VOUT = 24V
Burst Mode OPERATION
FIGURE 9 CIRCUIT
0.1
0.01 0.1 1 10
OUTPUT CURRENT (A)
37881 TA01b
37881f
1
1 page  
TYPICAL PERFORMANCE CHARACTERISTICS
LTC3788-1
Efficiency and Power Loss
vs Output Current
100
10000
90
80 1000
70
60 100
50
40 10
30
20
10
0
0.01
VIN = 12V
1
VOUT = 24V
FIGURE 9 CIRCUIT
0.1
0.1 1 10
OUTPUT CURRENT (A)
BURST EFFICIENCY
PULSE-SKIPPING
EFFICIENCY
CCM EFFICIENCY
37881 G01
BURST LOSS
PULSE-SKIPPING
LOSS
CCM LOSS
Efficiency vs Input Voltage
100
ILOAD = 2A
99 FIGURE 9 CIRCUIT
98
97 VOUT = 12V
96
VOUT = 24V
95
94
93
www.DataSheet4U.com 92
91
90
0
5 10 15 20
INPUT VOLTAGE (V)
25
37881 G03
Load Step
Burst Mode Operation
Efficiency and Power Loss
vs Output Current
100
10000
90
80 1000
70
60 100
50
40 10
30
20
10
0
0.00001 0.0001 0.001
VIN = 12V
1
VOUT = 24V
Burst Mode OPERATION
FIGURE 9 CIRCUIT
0.1
0.01 0.1 1 10
OUTPUT CURRENT (A)
BURST EFFICIENCY
BURST LOSS
37881 G02
Load Step
Forced Continuous Mode
LOAD STEP
2A/DIV
INDUCTOR
CURRENT
5A/DIV
VOUT
500mV/DIV
VIN = 12V
200μs/DIV
VOUT = 24V
FIGURE 9 CIRCUIT
Load Step
Pulse-Skipping Mode
37881 G04
LOAD STEP
2A/DIV
INDUCTOR
CURRENT
5A/DIV
VOUT
500mV/DIV
LOAD STEP
2A/DIV
INDUCTOR
CURRENT
5A/DIV
VOUT
500mV/DIV
VIN = 12V
200μs/DIV
VOUT = 24V
FIGURE 9 CIRCUIT
37881 G05
VIN = 12V
200μs/DIV
VOUT = 24V
FIGURE 9 CIRCUIT
37881 G06
37881f
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5 Page 
LTC3788-1
OPERATION (Refer to Block Diagram)
Main Control Loop
The LTC3788-1 uses a constant-frequency, current mode
step-up architecture with the two controller channels oper-
ating 180 degrees out-of-phase. During normal operation,
each external bottom MOSFET is turned on when the clock
for that channel sets the RS latch, and is turned off when
the main current comparator, ICMP, resets the RS latch.
The peak inductor current at which ICMP trips and resets
the latch is controlled by the voltage on the ITH pin, which
is the output of the error amplifier EA. The error amplifier
compares the output voltage feedback signal at the VFB
pin, (which is generated with an external resistor divider
connected across the output voltage, VOUT, to ground) to
the internal 1.200V reference voltage. When the load cur-
rent increases, it causes a slight decrease in VFB relative
to the reference, which causes the EA to increase the ITH
voltage until the average inductor current matches the
new load current.
After the bottom MOSFET is turned off each cycle, the
top MOSFET is turned on until either the inductor current
starts to reverse, as indicated by the current comparator
IR, or the beginning of the next clock cycle.
INTVCC/EXTVCC Power
Power for the top and bottom MOSFET drivers and most
wwwo.DthatearShineetet4rUn.acol mcircuitry is derived from the INTVCC pin.
When the EXTVCC pin is left open or tied to a voltage less
than 4.8V, the VBIAS LDO (low dropout linear regulator)
supplies 5.4V from VBIAS to INTVCC. If EXTVCC is taken
above 4.8V, the VBIAS LDO is turned off and an EXTVCC
LDO is turned on. Once enabled, the EXTVCC LDO supplies
5.4V from EXTVCC to INTVCC. Using the EXTVCC pin allows
the INTVCC power to be derived from a high efficiency
external source such as one of the LTC3788-1 switching
regulator outputs.
Shutdown and Start-Up
(RUN1, RUN2 and SS1, SS2 Pins)
The two channels of the LTC3788-1 can be independently
shut down using the RUN1 and RUN2 pins. Pulling either of
these pins below 1.28V shuts down the main control loop
for that controller. Pulling both pins below 0.7V disables
both controllers and most internal circuits, including the
INTVCC LDO’s. In this state, the LTC3788-1 draws only
8μA of quiescent current.
The RUN pin may be externally pulled up or driven directly
by logic. When driving the RUN pin with a low impedance
source, do not exceed the absolute maximum rating of
8V. The RUN pin has an internal 11V voltage clamp that
allows the RUN pin to be connected through a resistor to a
higher voltage (for example, VIN), as long as the maximum
current into the RUN pin does not exceed 100μA.
The start-up of each controller’s output voltage VOUT is
controlled by the voltage on the SS pin for that channel.
When the voltage on the SS pin is less than the 1.2V
internal reference, the LTC3788-1 regulates the VFB volt-
age to the SS pin voltage instead of the 1.2V reference.
This allows the SS pin to be used to program a soft-start
by connecting an external capacitor from the SS pin to
SGND. An internal 10μA pull-up current charges this
capacitor creating a voltage ramp on the SS pin. As the
SS voltage rises linearly from 0V to 1.2V (and beyond
up to INTVCC), the output voltage VOUT rises smoothly
to its final value.
Light Load Current Operation—Burst Mode Operation,
Pulse-Skipping or Continuous Conduction
(PLLIN/MODE Pin)
The LTC3788-1 can be enabled to enter high efficiency
Burst Mode operation, constant-frequency pulse-skip-
ping mode or forced continuous conduction mode at
low load currents. To select Burst Mode operation, tie
the PLLIN/ MODE pin to a ground (e.g., SGND). To se-
lect forced continuous operation, tie the PLLIN/MODE
pin to INTVCC. To select pulse-skipping mode, tie the
PLLIN/MODE pin to a DC voltage greater than 1.2V and
less than INTVCC – 0.5V.
When a controller is enabled for Burst Mode operation, the
minimum peak current in the inductor is set to approxi-
mately 30% of the maximum sense voltage even though
the voltage on the ITH pin indicates a lower value. If the
average inductor current is higher than the load current,
the error amplifier EA will decrease the voltage on the ITH
pin. When the ITH voltage drops below 0.425V, the internal
sleep signal goes high (enabling sleep mode) and both
external MOSFETs are turned off.
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11 Page | ||
| Páginas | Total 28 Páginas | |
| PDF Descargar | [ Datasheet LTC3788-1.PDF ] | |
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