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PDF LTC3859 Data sheet ( Hoja de datos )
| Número de pieza | LTC3859 | |
| Descripción | Buck/Buck/Boost Synchronous Controller | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURES
n Dual Buck Plus Single Boost Synchronous Controllers
n Outputs Remain in Regulation Through Cold Crank
Down to 2.5V
n Low Operating IQ: 55μA (One Channel On)
n Wide Bias Input Voltage Range: 4.5V to 38V
n Buck Output Voltage Range: 0.8V ≤ VOUT ≤ 24V
n Boost Output Voltage Up to 60V
n RSENSE or DCR Current Sensing
n 100% Duty Cycle for Boost Synchronous MOSFET
n Phase-Lockable Frequency (75kHz to 850kHz)
n Programmable Fixed Frequency (50kHz to 900kHz)
n Selectable Continuous, Pulse-Skipping or Low Ripple
Burst Mode® Operation at Light Loads
n Very Low Buck Dropout Operation: 99% Duty Cycle
n Adjustable Output Voltage Soft-Start or Tracking
n Low Shutdown IQ: 14μA
n Small 38-Pin 5mm × 7mm QFN and TSSOP Packages
APPLICATIONS
n Automotive Always-On and Start-Stop Systems
n Battery Operated Digital Devices
n Distributed DC Power Systems
L, LT, LTC, LTM, Burst Mode, OPTI-LOOP and μModule are registered trademarks and
No RSENSE is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners. Protected by U.S. Patents including 5481178, 5705919,
5929620, 6144194, 6177787, 6580258.
www.DataSheet4U.com
LTC3859
Low IQ, Triple Output,
Buck/Buck/Boost
Synchronous Controller
DESCRIPTION
The LTC®3859 is a high performance triple output (buck/
buck/boost) synchronous DC/DC switching regulator
controller that drives all N-channel power MOSFET stages.
Constant frequency current mode architecture allows a
phase-lockable switching frequency of up to 850kHz. The
LTC3859 operates from a wide 4.5V to 38V input supply
range. When biased from the output of the boost converter
or another auxiliary supply, the LTC3859 can operate from
an input supply as low as 2.5V after start-up.
The 55μA no-load quiescent current extends operating
runtime in battery powered systems. OPTI-LOOP com-
pensation allows the transient response to be optimized
over a wide range of output capacitance and ESR values.
The LTC3859 features a precision 0.8V reference for the
bucks, 1.2V reference for the boost and a power good
output indicator.
Independent TRACK/SS pins for each controller ramp the
output voltages during start-up. Current foldback limits
MOSFET heat dissipation during short-circuit conditions.
The PLLIN/MODE pin selects among Burst Mode opera-
tion, pulse-skipping mode, or continuous inductor current
mode at light loads.
TYPICAL APPLICATION
VOUT3
REGULATED AT 10V WHEN VIN < 10V
FOLLOWS VIN WHEN VIN > 10V
220μF
499k
1μF
VFB3
68.1k
VBIAS
TG1
VIN
2.5V TO 38V
(START-UP ABOVE 5V)
220μF
2mΩ
1.2μH
4.7μF
SW1, 2, 3
TG3 SW1
SW3 BG1
LTC3859
BG3
SENSE3–
SENSE3+
INTVCC
BOOST1, 2, 3
0.1μF
ITH1, 2, 3
SENSE1+
SENSE1–
VFB1
RUN1, 2, 3
EXTVCC
TG2
SW2
BG2
0.1μF
SENSE2+
TRACK/SS1, 2 SENSE2–
SS3 VFB2
PGND SGND
3859 TA01
4.9μH 6mΩ
VOUT1
5V
5A
68.1k 357k
220μF
6.5μH 8mΩ
VOUT2
8.5V
3A
68.1k 649k
68μF
Efficiency vs Input Voltage
100
95 VOUT2 = 8.5V
90 VOUT1 = 5V
85
80
75
70
65
60
55 FIGURE 12 CIRCUIT
ILOAD = 2A
50
0 5 10 15 20 25 30
INPUT VOLTAGE (V)
35 40
3859 TA01b
3859f
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LTC3859
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating junction
temperature range, otherwise specifications are at TJ ≈ TA = 25°C. VBIAS = 12V, VRUN1,2,3 = 5V, EXTVCC = 0V unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN TYP MAX UNITS
VINTVCCEXT
Internal VCC Voltage
VLDOEXT
INTVCC Load Regulation
VEXTVCC
EXTVCC Switchover Voltage
VLDOHYS
EXTVCC Hysteresis
Oscillator and Phase-Locked Loop
6V < VEXTVCC < 13V, IINTVCC = 0mA
ICC = 0mA to 50mA, VEXTVCC = 8.5V
EXTVCC Ramping Positive
5.0 5.4 5.6
0.7 2
4.5 4.7
200
V
%
V
mV
f25k Programmable Frequency
f65k Programmable Frequency
f105k Programmable Frequency
fLOW Low Fixed Frequency
fHIGH High Fixed Frequency
fSYNC
Synchronizable Frequency
PGOOD1 Output
RFREQ = 25k; PLLIN/MODE = DC Voltage
RFREQ = 65k; PLLIN/MODE = DC Voltage
RFREQ = 105k; PLLIN/MODE = DC Voltage
VFREQ = 0V PLLIN/MODE = DC Voltage
VFREQ = INTVCC; PLLIN/MODE = DC Voltage
PLLIN/MODE = External Clock
115
375 440 505
835
320 350 380
485 535 585
l 75
850
kHz
kHz
kHz
kHz
kHz
kHz
VPGL1
IPGOOD1
VPG1
PGOOD1 Voltage Low
PGOOD1 Leakage Current
PGOOD1 Trip Level
TPG1 Delay For Reporting a Fault
OV3 Boost Overvoltage Indicator Output
IPGOOD1 = 2mA
VPGOOD1 = 5V
VFB1 with Respect to Set Regulated Voltage
VFB1 Ramping Negative
Hysteresis
VFB1 Ramping Positive
Hysteresis
0.2 0.4
±1
–13 –10 –7
2.5
7 10 13
2.5
20
V
μA
%
%
%
%
μs
VOV3L
IOV3
VOV
OV3 Voltage Low
OV3 Leakage Current
OV3 Trip Level
BOOST3 Charge Pump
IOV3 = 2mA
VOV3 = 5V
VFB With Respect to Set Regulated Voltage
Hysteresis
0.2 0.4
±1
6 10 13
1.5
V
μA
%
%
IBST3 BOOST3 Charge Pump Available Output VBOOST3 = 16V; VSW3 = 12V;
Current
Forced Continuous Mode
65 μA
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 LTC3859 is tested under pulsed conditions such that TJ ≈ TA.
The LTC3859E is guaranteed to meet performance specifications from
0°C to 125°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 LTC3859I is guaranteed over the full
–40°C to 125°C operating junction temperature range.
Note 3: TJ is calculated from the ambient temperature TA and power
dissipation PD according to the following formula:
TJ = TA + (PD • θJA)
where θJA = 34°C/W for the QFN package and θJA = 25°C/W for the TSSOP
package.
Note 4: The LTC3859 is tested in a feedback loop that servos VITH1,2,3 to a
specified voltage and measures the resultant VFB1,2,3. The specification at
85°C is not tested in production. This specification is assured by design,
characterization and correlation to production testing at 125°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: See Minimum On-Time Considerations in the Applications
Information section.
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LTC3859
PIN FUNCTIONS (QFN/TSSOP)
TRACK/SS1, TRACK/SS2, SS3 (Pins 34, 16, 3/Pins 38,
20, 7): External Tracking and Soft-Start Input. For the buck
channels, the LTC3859 regulates the VFB1,2 voltage to the
smaller of 0.8V, or the voltage on the TRACK/SS1,2 pin. For
the boost channel, the LTC3859 regulates the VFB3 voltage
to the smaller of 1.2V, or the voltage on the SS3 pin. An
internal 1μA pull-up current source is connected to this pin.
A capacitor to ground at this pin sets the ramp time to final
regulated output voltage. Alternatively, a resistor divider on
another voltage supply connected to the TRACK/SS pins
of the buck channels allow the LTC3859 buck outputs to
track the other supply during start-up.
ITH1, ITH2, ITH3 (Pins 35, 15, 7/Pins 1, 19, 11): Error
Amplifier Outputs and Switching Regulator Compensation
Points. Each associated channel’s current comparator trip
point increases.
VFB1, VFB2, VFB3 (Pins 36, 14, 6/Pins 2, 18, 10): Receives
the remotely sensed feedback voltage for each controller
from an external resistive divider across the output.
SENSE1+, SENSE2+, SENSE3+ (Pins 37, 13, 4/Pins 3, 17,
8): The (+) Input to the Differential Current Comparators.
The ITH pin voltage and controlled offsets between the
SENSE– and SENSE+ pins in conjunction with RSENSE set the
current trip threshold. For the boost channel, the SENSE3+
pin supplies current to the current comparator.
SENSE1–, SENSE2–, SENSE3– (Pins 38, 12, 5/Pins 4,
16, 9): The (–) Input to the Differential Current Compara-
tors. When SENSE1,2– for the buck channels is greater
than INTVCC, then SENSE1,2– pin supplies current to the
current comparator.
PGND (Exposed Pad Pin 39): Driver Power Ground. Con-
nects to the sources of bottom (synchronous) N-channel
MOSFETs and the (–) terminal(s) of CIN. The exposed
pad must be soldered to the PCB for rated electrical and
thermal performance.
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| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet LTC3859.PDF ] | |
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