|
|
PDF LTC3853 Data sheet ( Hoja de datos )
| Número de pieza | LTC3853 | |
| Descripción | Multiphase Synchronous Step-Down Controller | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
|
Hay una vista previa y un enlace de descarga de LTC3853 (archivo pdf) en la parte inferior de esta página. Total 30 Páginas | ||
|
No Preview Available !
LTC3853
Triple Output,
Multiphase Synchronous
Step-Down Controller
FEATURESwww.datasheet4u.com
DESCRIPTION
n Triple, 120° Phased Controllers Reduce Required
Input Capacitance and Power Supply Induced Noise
n Configurable as a 180° Dual Phase Controller Plus a
Single Phase Controller
n The Third Phase Can Regulate Up to a 13.5V Output
n High Efficiency: Up to 92%
n RSENSE or DCR Current Sensing
n ±0.75% 0.8V Output Voltage Accuracy
n Phase-Lockable Fixed Frequency 250kHz to 750kHz
n Supports Pre-Biased Outputs
n Dual N-Channel MOSFET Synchronous Drive
n Wide VIN Range: 4.5V to 24V Operation (28V Abs Max)
n Adjustable Soft-Start Current Ramping or Tracking
n Foldback Output Current Limiting
n Output Overvoltage Protection
n Dual Power Good Output Voltage Monitors
n 40-Lead 6mm × 6mm QFN Package
L, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners. Protected by U.S. Patents,
including 5481178, 5705919, 5929620, 6100678, 6144194, 6177787, 6304066, 6580258.
The LTC®3853 is a high performance triple output step-
down switching regulator controller that drives all N-chan-
nel synchronous power MOSFET stages. Power loss and
supply noise are minimized by operating the output stages
out of phase. The part can be configured as a dual phase
controller plus a single phase controller if needed. The
part can also be configured to provide a single 3-phase
output for even higher output currents.
A wide 4.5V to 24V (28V maximum) input voltage sup-
ply range encompasses most battery chemistries and
intermediate bus voltages. Phase 3 can regulate output
voltages up to 13.5V. A constant frequency current mode
architecture allows for a phase-lockable frequency up to
750kHz.
Independent TK/SS pins for each output ramps the output
voltages and can be configured for coincident or ratiometric
tracking. Current foldback limits MOSFET heat dissipation
during short-circuit conditions. The MODE/PLLIN pin
selects among Burst Mode® operation, pulse-skipping or
continuous inductor current modes.
TYPICAL APPLICATION
High Efficiency Triple 5V/3.3V/1.2V Step-Down Converter
2.2μH
2.2k
0.1μF
VOUT1
5V
5A
105k
+ 100μF
10V
220pF
20k
4.7μF
VIN
INTVCC
TG1
PGOOD12
PGOOD3
TG2
BOOST1,2,3
SW1 SW2
BG1 LTC3853 BG2
fIN
500kHz
MODE/PLLIN
PGND
ILIM FREQ/PLLFLTR
SENSE1+
SENSE1–
SENSE2+
SENSE2–
VFB2
1500pF
15k
VFB1
ITH1,2,3
RUN1,2,3
TG3
VFB3
SGND
SW3
BG3
SENSE3+
SENSE3–
TK/SS1,2,3
0.1μF
0.1μF
SW1,2,3
10nF
10k
2.2μH
2.2k
0.1μF
63.4k
20k
VOUT2
3.3V
5A
+
100μF
6V
VIN
7V TO 24V
22μF
50V
1μH
1k
0.1μF
10k
20k
VOUT3
1.2V
5A
+ 100μF
6V
3853f
1
1 page  
TYPICAL PERFORMANCE CHARACTERISTICS
LTC3853
Efficiency vs Output Current
and Mode
www.da1ta00sheet4u.com
90
80
70
BURST
60
50
DCM CCM
40
30
20
10
0
1.00E-02
VIN = 12V
VOUT = 1.8V
FIGURE 15 MODIFIED
WITH DCR SENSING
1.00E-01
1.00E+00
LOAD CURRENT (mA)
1.00E+01
3853 G01
Efficiency vs Output Current
and Mode
100
90
80
BURST
70
60
50
CCM
40 DCM
30
20
10
0
1.00E-02
VIN = 12V
VOUT = 3.3V
FIGURE 15 MODIFIED
WITH DCR SENSING
1.00E-01
1.00E+00
LOAD CURRENT (mA)
1.00E+01
3853 G02
Efficiency and Power Loss
vs Input Voltage
100 2.0
95
90 EFFICIENCY
85
1.8
1.6
1.4
1.2
80 1.0
75 POWER LOSS
0.8
0.6
70
65
VOUT = 3.3V
IOUT = 2A
FIGURE 15 MODIFIED
0.4
0.2
WITH DCR SENSING
60 0
0 5 10 15 20 25 30
INPUT VOLTAGE (V)
3853 G03
Load Step
(Burst Mode Operation)
Load Step
(Forced Continuous Mode)
ILOAD
2A/DIV
ILOAD
2A/DIV
IL
2A/DIV
VOUT
100mV/DIV
AC COUPLED
VIN = 12V
40μs/DIV
VOUT = 3.3V
ILOAD = 0A TO 3A
FIGURE 15 CIRCUIT
3853 G04
IL
2A/DIV
VOUT
100mV/DIV
AC COUPLED
VIN = 12V
40μs/DIV
VOUT = 3.3V
ILOAD = 0A TO 3A
FIGURE 15 CIRCUIT
3853 G05
Load Step
(Pulse Skip Mode)
ILOAD
2A/DIV
IL
2A/DIV
VOUT
100mV/DIV
AC COUPLED
VIN = 12V
40μs/DIV
VOUT = 3.3V
ILOAD = 0A TO 3A
FIGURE 15 CIRCUIT
3853 G06
Inductor Current at Light Load
FORCED
CONTINUOUS
MODE
2A/DIV
Burst Mode
OPERATION
2A/DIV
PULSE SKIPPING
MODE
2A/DIV
VIN = 12
1μs/DIV
VOUT = 1.8V
ILOAD = 100mA
FIGURE 15 CIRCUIT
3853 G07
3853f
5
5 Page 
LTC3853
OPERATION
Main Control Loop
The LTC3853 is a constant-frequency, current mode
wwws.dtaetpas-hdeoewt4nu.ccoomntroller with three channels operating 120
degrees out-of-phase. During normal operation, each
top MOSFET is turned on when the clock for that channel
sets the RS latch, and turned off when the main current
comparator, ICMP, resets the RS latch. The peak inductor
current at which ICMP resets the RS latch is controlled by
the voltage on the ITH pin, which is the output of each error
amplifier, EA. The VFB pin receives the voltage feedback
signal, which is compared to the internal reference voltage
by the EA. When the load current increases, it causes a
slight decrease in VFB relative to the 0.8V reference, which
in turn causes the ITH voltage to increase until the average
inductor current matches the new load current. After the
top MOSFET has turned off, the bottom MOSFET is turned
on until either the inductor current starts to reverse, as
indicated by the reverse current comparator IREV, or the
beginning of the next cycle.
INTVCC/EXTVCC/DRVCC12 Power
Power for the top and bottom MOSFET drivers of phase 3
and most other internal circuitry is derived from the
INTVCC pin. DRVCC12 provides driver power for phase 1
and phase 2. This pin must be externally tied to INTVCC.
If EXTVCC is taken above 4.7V, the 5V regulator is turned
off and an internal switch is turned on connecting EXTVCC.
Using the EXTVCC pin allows the INTVCC power to be derived
from a high efficiency external source such as one of the
LTC3853 switching regulator outputs.
Each top MOSFET driver is biased from the floating boot-
strap capacitor, CB, which normally recharges during each
off cycle through an external diode when the top MOSFET
turns off. If the input voltage, VIN, decreases to a voltage
close to VOUT, the loop may enter dropout and attempt to
turn on the top MOSFET continuously. The dropout detec-
tor detects this and forces the top MOSFET off for about
one-twelfth of the clock period every fifth cycle to allow
CB to recharge. However, it is recommended that there is
always a load be present during the drop-out transition
to ensure CB is recharged.
Shutdown and Start-Up (RUN1, RUN2, RUN3 and
TK/SS1, TK/SS2, TK/SS3 Pins)
The three channels of the LTC3853 can be independently
shut down using the RUN1, RUN2 and RUN3 pins. Pulling
any of these pins below 1.2V shuts down the main control
loop for that controller. Pulling all pins low disables all
three controllers and most internal circuits, including the
INTVCC regulator. Releasing any RUN pin allows an internal
0.5μA current to pull up the pin and enable that control-
ler. Alternatively, the RUN pin may be externally pulled up
or driven directly by logic. Be careful not to exceed the
absolute maximum rating of 6V on this pin.
The start-up of each controller’s output voltage VOUT is
controlled by the voltage on the TK/SS1, TK/SS2 and
TK/SS3 pins. When the voltage on the TK/SS pin is less
than the 0.8V internal reference, the LTC3853 regulates
the VFB voltage to the TK/SS pin voltage instead of the
0.8V reference. This allows the TK/SS pin to be used to
program a soft-start by connecting an external capacitor
from the TK/SS pin to SGND. An internal 1.3μA pull-up
current charges this capacitor, creating a voltage ramp
on the TK/SS pin. As the TK/SS voltage rises linearly
from 0V to 0.8V (and beyond), the output voltage VOUT
rises smoothly from zero to its final value. Alternatively
the TK/SS pin can be used to cause the start-up of VOUT
to “track” that of another supply. Typically, this requires
connecting to the TK/SS pin an external resistor divider
from the other supply to ground (see the Applications
Information section). When the corresponding RUN pin
is pulled low to disable a controller, or when INTVCC drops
below its undervoltage lockout threshold of 3.35V, the
TK/SS pin is pulled low by an internal MOSFET. When in
undervoltage lockout, all controllers are disabled and the
external MOSFETs are held off.
Light Load Current Operation (Burst Mode Operation,
Pulse Skipping or Continuous Conduction)
The LTC3853 can be enabled to enter high efficiency Burst
Mode operation, constant-frequency pulse skipping mode,
or forced continuous conduction mode. To select forced
continuous operation, tie the MODE/PLLIN pin to a DC
3853f
11
11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet LTC3853.PDF ] | |
Hoja de datos destacado
| Número de pieza | Descripción | Fabricantes |
| LTC3850 | 2-Phase Synchronous Step-Down Switching Controller | Linear Technology |
| LTC3850-1 | 2-Phase Synchronous Step-Down Switching Controller | Linear Technology |
| LTC3850-2 | 2-Phase Synchronous Step-Down Switching Controller | Linear Technology |
| LTC3851 | Synchronous Step-Down Switching Regulator Controller | Linear Technology |
| Número de pieza | Descripción | Fabricantes |
| SLA6805M | High Voltage 3 phase Motor Driver IC. |
 Sanken |
| SDC1742 | 12- and 14-Bit Hybrid Synchro / Resolver-to-Digital Converters. |
 Analog Devices |
|
DataSheet.es es una pagina web que funciona como un repositorio de manuales o hoja de datos de muchos de los productos más populares, |
| DataSheet.es | 2020 | Privacy Policy | Contacto | Buscar |