|
|
PDF LTC3891 Data sheet ( Hoja de datos )
| Número de pieza | LTC3891 | |
| Descripción | 60V Synchronous Step-Down Controller | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
|
Hay una vista previa y un enlace de descarga de LTC3891 (archivo pdf) en la parte inferior de esta página. Total 30 Páginas | ||
|
No Preview Available !
LTC3891
Low IQ, 60V Synchronous
Step-Down Controller
FEATURES
n Wide VIN Range: 4V to 60V (65V Abs Max)
n Low Operating IQ: 50μA
n Wide Output Voltage Range: 0.8V ≤ VOUT ≤ 24V
n RSENSE or DCR Current Sensing
n Phase-Lockable Frequency (75kHz to 750kHz)
n Programmable Fixed Frequency (50kHz to 900kHz)
n Selectable Continuous, Pulse-Skipping or Low Ripple
Burst Mode® Operation at Light Load
n Selectable Current Limit
n Very Low Dropout Operation: 99% Duty Cycle
n Adjustable Output Voltage Soft-Start or Tracking
n Power Good Output Voltage Monitor
n Output Overvoltage Protection
n Low Shutdown IQ: < 14μA
n Internal LDO Powers Gate Drive from VIN or EXTVCC
n No Current Foldback During Start-Up
n Small 20-Pin 3mm × 4mm QFN and TSSOP Packages
APPLICATIONS
n Automotive Always-On Systems
n Battery Powered Digital Devices
n Distributed DC Power Systems
DESCRIPTION
The LTC®3891 is a high performance step-down switching
regulator DC/DC controller that drives an all N-channel
synchronous power MOSFET stage. A constant fre-
quency current mode architecture allows a phase-lockable
frequency of up to 750kHz.
The 50μA no-load quiescent current extends operating run
time in battery-powered systems. OPTI-LOOP® compensa-
tion allows the transient response to be optimized over
a wide range of output capacitance and ESR values. The
LTC3891 features a precision 0.8V reference and power
good output indicator. A wide 4V to 60V input supply range
encompasses a wide range of intermediate bus voltages
and battery chemistries. The output voltage of the LTC3891
can be programmed between 0.8V to 24V.
The TRACK/SS pin ramps the output voltages during
start-up. Current foldback limits MOSFET heat dissipation
during short-circuit conditions. The PLLIN/MODE pin se-
lects among Burst Mode operation, pulse-skipping mode,
or continuous conduction mode at light loads.
L, LT, LTC, LTM, OPTI-LOOP, Burst Mode, Linear Technology and the Linear logo are registered
trademarks of Linear Technology Corporation. All other trademarks are the property of their
respective owners. Patents, including 5481178, 5705919, 6611131, 6498466, 6580258,
7230497.
TYPICAL APPLICATION
VIN
4V TO 60V
High Efficiency 3.3V Step-Down Converter
22µF
VIN LTC3891 INTVCC
2.2µF
41.2k
2200pF
10k
100pF
0.1µF
FREQ
ITH
TRACK/SS
SGND
TG
BOOST
SW
BG
SENSE+
SENSE–
VFB
PGOOD
0.1µF
4.7µH
100k
INTVCC
8mΩ
150µF
VOUT
3.3V
5A
100k
31.6k
3891 TA01a
Efficiency and Power Loss vs
Output Current
100 VIN = 12V
90 VOUT = 3.3V
80
10000
1000
70
60 100
50
40 10
30
20 1
10
0
0.0001
0.001 0.01 0.1
1
OUTPUT CURRENT (A)
0.1
10
3891 TA01b
3891fa
1
1 page  
ELECTRICAL CHARACTERISTICS
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: The LTC3891 is tested under pulsed load conditions such that
TJ ≈ TA. The LTC3891E is guaranteed to meet performance specifications
from 0°C to 85°C. Specifications over the –40°C to 125°C operating
junction temperature range are assured by design, characterization and
correlation with statistical process controls. The LTC3891I is guaranteed
over the –40°C to 125°C operating junction temperature range, the
LTC3891H is guaranteed over the –40°C to 150°C operating junction
temperature range and the LTC3891MP is tested and guaranteed over
the –55°C to 150°C operating junction temperature range. High junction
temperatures degrade operating lifetimes; operating lifetime is derated
for junction temperatures greater than 125°C. Note that the maximum
ambient temperature consistent with these specifications is determined by
specific operating conditions in conjunction with board layout, the rated
package thermal impedance and other environmental factors.
Note 3: The junction temperature (TJ, in °C) is calculated from the ambient
temperature (TA, in °C) and power dissipation (PD, in Watts) according to
the formula:
TJ = TA + (PD • θJA), where θJA is 43°C/W for the QFN or 38°C/W for the
TSSOP.
LTC3891
Note 4: The LTC3891 is tested in a feedback loop that servos VITH to a
specified voltage and measures the resultant VFB. The specification at
85°C is not tested in production and is assured by design, characterization
and correlation to production testing at other temperatures (125°C for
the LTC3891E/LTC3891I, 150°C for the LTC3891H/LTC3891MP). For the
LTC3891MP, the specification at –40°C is not tested in production and is
assured by design, characterization and correlation to production testing
at –55°C.
Note 5: Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency. See Applications Information.
Note 6: Rise and fall times are measured using 10% and 90% levels. Delay
times are measured using 50% levels
Note 7: The minimum on-time condition is specified for an inductor
peak-to-peak ripple current ≥ 40% of IMAX (See Minimum On-Time
Considerations in the Applications Information section).
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency and Power Loss vs
Output Current
100 VIN = 12V
90 VOUT = 3.3V
BURST EFFICIENCY
80
10000
1000
70 FCM LOSS
60
100
50
40
PULSE-SKIPPING
LOSS
BURST LOSS
10
30
20
FCM EFFICIENCY
1
10
0
0.0001
PULSE-SKIPPING
EFFICIENCY
0.001 0.01 0.1
1
OUTPUT CURRENT (A)
0.1
10
FIGURE 12 CIRCUIT
3891 G01
Efficiency vs Output Current
100
90 VOUT = 8.5V
80
VOUT = 3.3V
70
60
50
40
30
20
Burst Mode OPERATION
10
0
VIN = 12V
0.0001 0.001 0.01 0.1
OUTPUT CURRENT (A)
1
FIGURES 12, 14 CIRCUITS
10
3891 G02
Efficiency vs Input Voltage
100
98
96 VOUT = 8.5V
94
92
90
88 VOUT = 3.3V
86
84
82
80
ILOAD = 2A
0 5 10 15 20 25 30 35 40 45 50 55 60
INPUT VOLTAGE (V)
FIGURES 12, 14 CIRCUITS
3891 G03
3891fa
5
5 Page 
LTC3891
OPERATION
Main Control Loop
The LTC3891 uses a constant frequency, current mode
step-down architecture. During normal operation, the
external top 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 0.800V 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 top MOSFET is turned off each cycle, the bottom
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
other internal circuitry is derived from the INTVCC pin.
When the EXTVCC pin is tied to a voltage less than 4.7V,
the VIN LDO (low dropout linear regulator) supplies 5.1V
from VIN to INTVCC. If EXTVCC is taken above 4.7V, the VIN
LDO is turned off and an EXTVCC LDO is turned on. Once
enabled, the EXTVCC LDO supplies 5.1V 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 LTC3891 switching regulator outputs.
The top MOSFET driver is biased from the floating bootstrap
capacitor, CB, which normally recharges during each 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 detector
detects this and forces the top MOSFET off for about one
twelfth of the clock period every tenth cycle to allow CB
to recharge.
Shutdown and Start-Up (RUN, TRACK/SS Pins)
The LTC3891 can be shut down using the RUN pin. Pulling
this pin below 1.16V shuts down the main control loop.
Pulling the RUN pin below 0.7V disables the controller
and most internal circuits, including the INTVCC LDOs.
In this state, the LTC3891 draws only 14μA of quiescent
current.
Releasing the RUN pin allows a small internal current to
pull up the pin to enable the controller. The RUN pin has
a 7μA pull-up which is designed to be large enough so
that the RUN pin can be safely floated (to always enable
the controller) without worry of condensation or other
small board leakage pulling the pin down. This is ideal
for always-on applications where the controller is enabled
continuously and never shut down.
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), so long as the maximum
current into the RUN pin does not exceed 100μA.
The RUN pin can also be implemented as a UVLO by
connecting it to the output of an external resistor divider
network off VIN (see Applications Information section).
The start-up of the controller’s output voltage VOUT is
controlled by the voltage on the TRACK/SS pin. When the
voltage on the TRACK/SS pin is less than the 0.8V internal
reference, the LTC3891 regulates the VFB voltage to the
TRACK/SS pin voltage instead of the 0.8V reference. This
allows the TRACK/SS pin to be used to program a soft-start
by connecting an external capacitor from the TRACK/SS
pin to SGND. An internal 10μA pull-up current charges
this capacitor creating a voltage ramp on the TRACK/SS
pin. As the TRACK/SS voltage rises linearly from 0V to
0.8V (and beyond up to 5V), the output voltage VOUT rises
smoothly from zero to its final value. Alternatively the
TRACK/SS pin can be used to cause the start-up of VOUT
to track that of another supply. Typically, this requires
connecting to the TRACK/SS pin an external resistor
divider from the other supply to ground (see Applications
Information section).
3891fa
11
11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet LTC3891.PDF ] | |
Hoja de datos destacado
| Número de pieza | Descripción | Fabricantes |
| LTC3890 | 2-Phase Synchronous Step-Down DC/DC Controller | Linear Technology |
| LTC3890-1 | 2-Phase Synchronous Step-Down DC/DC Controller |  Linear |
| LTC3890-2 | 2-Phase Synchronous Step-Down DC/DC Controller | Linear Technology |
| LTC3890-3 | 2-Phase Synchronous Step-Down DC/DC Controller | Linear |
| 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 |