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PDF LTC3787 Data sheet ( Hoja de datos )
| Número de pieza | LTC3787 | |
| Descripción | PolyPhase Synchronous Boost Controller | |
| Fabricantes | Linear Technology Corporation | |
| Logotipo |  |
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DataSheet.in
LTC3787
PolyPhase Synchronous
Boost Controller
Features
n 2-Phase Operation Reduces Required Input and
Output Capacitance and Power Supply Induced Noise
n Synchronous Operation for Highest Efficiency and
Reduced Heat Dissipation
n Wide VIN Range: 4.5V to 38V (40V Abs Max) and
Operates Down to 2.5V After Start-Up
n Output Voltage Up to 60V
n ±1% 1.200V Reference Voltage
n RSENSE or Inductor DCR Current Sensing
n 100% Duty Cycle Capability for Synchronous MOSFET
n Low Quiescent Current: 135μA
n Phase-Lockable Frequency (75kHz to 850kHz)
n Programmable Fixed Frequency (50kHz to 900kHz)
n Power Good Output Voltage Monitor
n Low Shutdown Current, IQ < 8µA
n Internal LDO Powers Gate Drive from VBIAS or EXTVCC
n Thermally Enhanced Low Profile 28-Pin 4mm × 5mm
QFN Package and Narrow SSOP Package
Applications
n Industrial
n Automotive
n Medical
n Military
Description
The LTC®3787 is a high performance PolyPhase® single
output synchronous boost converter controller that drives
two N-channel power MOSFET stages out-of-phase.
Multiphase operation reduces input and output capacitor
requirements and allows the use of smaller inductors than
the single-phase equivalent. Synchronous rectification in-
creases efficiency, reduces power losses and eases thermal
requirements, enabling high power boost applications.
A 4.5V to 38V input supply range encompasses a wide
range of system architectures and battery chemistries.
When biased from the output of the boost converter or
another auxiliary supply, the LTC3787 can operate from
an input supply as low as 2.5V after start-up. The operat-
ing frequency can be set for a 50kHz to 900kHz range or
synchronized to an external clock using the internal PLL.
PolyPhase operation allows the LTC3787 to be configured
for 2-, 3-, 4-, 6- and 12-phase operation.
The SS pin ramps the output voltage during start-up. The
PLLIN/MODE pin selects Burst Mode® operation, pulse-
skipping mode or forced continuous mode at light loads.
L, LT, LTC, LTM, Linear Technology, Burst Mode, OPTI-LOOP, PolyPhase 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
12V to 24V/10A 2-Phase Synchronous Boost Converter
VIN 4.5V TO 24V START-UP VOLTAGE
OPERATES THROUGH TRANSIENTS DOWN TO 2.5V
VIN
4mΩ
4.7µF
4.7µF
TG1 VBIAS INTVCC TG2
3.3µH
BOOST1
0.1µF
SW1
BOOST2
0.1µF
SW2
BG1 LTC3787
SENSE1+
BG2
232k
SENSE1–
SENSE2+
VFB
FREQ
SENSE2–
PLLIN/MODE
PGND
12.1k
15nF
8.66k
ITH SS SGND
100pF
0.1µF
4mΩ
47µF
3.3µH
VOUT
24V AT 10A
220µF
3787 TA01a
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
VOUT = 24V
1
Burst Mode OPERATION
FIGURE 10 CIRCUIT
0.1
0.01 0.1 1 10
OUTPUT CURRENT (A)
BURST EFFICIENCY
BURST LOSS
3787 TA01b
3787f
1 page  
DataSheet.in
Typical Performance Characteristics
LTC3787
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 10 CIRCUIT
0.1
0.1 1 10
OUTPUT CURRENT (A)
3787 G01
BURST EFFICIENCY
BURST LOSS
PULSE-SKIPPING
PULSE-SKIPPING
EFFICIENCY
LOSS
FORCED CONTINUOUS
FORCED CONTINUOUS
MODE EFFICIENCY
MODE LOSS
Efficiency vs Load Current
100 VIN = 12V
99 ILOAD = 2A
98 FIGURE 10 CIRCUIT
97
96 VOUT = 12V
95
VOUT = 24V
94
93
92
91
90
0
5 10 15 20
INPUT VOLTAGE (V)
25
3787 G03
Load Step
Burst Mode Operation
LOAD STEP
5A/DIV
INDUCTOR
CURRENT
5A/DIV
VOUT
500mV/DIV
VIN = 12V
200µs/DIV
VOUT = 24V
LOAD STEP FROM 100mA TO 5A
FIGURE 10 CIRCUIT
3787 G05
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
VOUT = 24V
1
Burst Mode OPERATION
FIGURE 10 CIRCUIT
0.1
0.01 0.1 1 10
OUTPUT CURRENT (A)
BURST EFFICIENCY
BURST LOSS
3787 G02
Load Step
Forced Continuous Mode
LOAD STEP
5A/DIV
INDUCTOR
CURRENT
5A/DIV
VOUT
500mV/DIV
VIN = 12V
200µs/DIV
VOUT = 24V
LOAD STEP FROM 100mA TO 5A
FIGURE 10 CIRCUIT
Load Step
Pulse-Skipping Mode
LOAD STEP
5A/DIV
INDUCTOR
CURRENT
5A/DIV
VOUT
500mV/DIV
VIN = 12V
200µs/DIV
VOUT = 24V
LOAD STEP FROM 100mA TO 5A
FIGURE 10 CIRCUIT
3787 G04
3787 G06
3787f
5 Page 
DataSheet.in
Block Diagram
PHASMD
CLKOUT
FREQ
20µA
CLK2
VCO CLK1
PFD
PLLIN/
MODE
100k
ILIM
VIN
EXTVCC
+
4.8V –
5.4V
LDO
EN
SYNC
DET
CURRENT
LIMIT
5.4V
LDO
EN
INTVCC
SHDN
–+
3.8V
SGND
LTC3787
DUPLICATE FOR SECOND CONTROLLER CHANNEL
S
RQ
SHDN
SWITCHING
LOGIC
AND
CHARGE
PUMP
BOOST
TG
SW
INTVCC
BG
0.425V
+
–
SLEEP
–
ICMP+
–+
2.8V
0.7V
SLOPE COMP
+
+ – –IREV
2mV
SENSE –
SENSE+
SENS LO
+
– 2.5V
+
EA – 1.2V
– SS
VFB
0.5µA/
4.5µA
11V
SHDN
RUN
SENS
LO
+
OV –
1.32V
ITH
10µA
SS
1.32V
VFB
1.08V
CSS
+
–
+
–
PGOOD
INTVCC
DB
CB
PGND
L
VOUT
COUT
RSENSE
VIN
CIN
CC
CC2 RC
3787 BD
Operation
Main Control Loop
The LTC3787 uses a constant-frequency, current mode
step-up architecture with the two controller channels
operating 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. In a boost converter,
the required inductor current is determined by the load
current, VIN and VOUT. When the load current 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 in each channel matches the new
requirement based on 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.
3787f
11
11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet LTC3787.PDF ] | |
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