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PDF LTC3826 Data sheet ( Hoja de datos )
| Número de pieza | LTC3826 | |
| Descripción | 2-Phase Synchronous Step-Down Controller | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC3826
30µA IQ, Dual, 2-Phase
Synchronous Step-Down Controller
FEATURES
DESCRIPTION
wwwn.datWasihdeeet4Ouu.ctopmut Voltage Range: 0.8V ≤ VOUT ≤ 10V
n Ultralow Operating IQ: 30μA (One Channel On)
n Out-of-Phase Controllers Reduce Required Input
Capacitance and Power Supply Induced Noise
n OPTI-LOOP® Compensation Minimizes COUT
n ±1% Output Voltage Accuracy
n Wide VIN Range: 4V to 36V Operation
n Phase-Lockable Fixed Frequency 140kHz to 650kHz
n Selectable Continuous, Pulse Skipping or Low Ripple
Burst Mode® Operation at Light Loads
n Dual N-Channel MOSFET Synchronous Drive
n Very Low Dropout Operation: 99% Duty Cycle
n Adjustable Output Voltage Soft-Start or Tracking
n Output Current Foldback Limiting
n Power Good Output Voltage Monitor
n Output Overvoltage Protection
n Low Shutdown IQ: 4μA
n Internal LDO Powers Gate Drive from VIN or VOUT
n Small 5mm × 5mm QFN Package
APPLICATIONS
n Automotive Systems
n Battery-Operated Digital Devices
n Distributed DC Power Systems
The LTC®3826 is a high performance dual step-down
switching regulator controller that drives all N-channel
synchronous power MOSFET stages. A constant frequency
current mode architecture allows a phase-lockable fre-
quency of up to 650kHz. Power loss and noise due to the
ESR of the input capacitor are minimized by operating the
two controller output stages out of phase.
The 30μA no-load quiescent current extends operating
life 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
LTC3826 features a precision 0.8V reference and a power
good output indicator. A wide 4V to 36V input supply range
encompasses all battery chemistries.
Independent TRACK/SS pins for each controller ramp the
output voltage 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 cur-
rent mode at light loads. For a leaded package version
(28-lead SSOP), see the LTC3826-1 data sheet.
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
Burst Mode and OPTI-LOOP are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners. Protected by U.S. Patents,
including 5481178, 5929620, 6177787, 6144194, 5408150, 6580258, 6304066, 5705919.
TYPICAL APPLICATION
VOUT1
3.3V
5A
High Efficiency Dual 8.5V/3.3V Step-Down Converter
3.3μH
0.015Ω
62.5k
150μF
0.1μF
VIN
TG1
INTVCC
TG2
BOOST1
SW1
BG1
LTC3826
SENSE1+
BOOST2
SW2
BG2
PGND
SENSE2+
SENSE1–
SENSE2–
VFB1
VFB2
ITH1 ITH2
20k 220pF TRACK/SS1 SGND TRACK/SS2
15k 0.1μF
0.1μF
4.7μF
0.1μF
22μF
50V
VIN
4V TO 36V
7.2μH
220pF
15k
0.015Ω
192.5k
20k
VOUT2
8.5V
3.5A
150μF
3826 TA01
Efficiency and Power Loss
vs Load Current
100 10000
90
80 1000
70
60 100
50
40 10
30
20 1
10
0
0.00001 0.0001 0.001
FIGURE 13 CIRCUIT
0.1
0.01 0.1 1 10
OUTPUT CURRENT (A)
3826 TA01b
3826fc
1
1 page  
TYPICAL PERFORMANCE CHARACTERISTICS
LTC3826
Efficiency and Power Loss
vs Output Current
www.dat1a0s0heet4u.com
Burst Mode OPERATION
90 PULSE SKIPPING MODE
80
FORCED
CONTINUOUS
70
10000
1000
60 100
50
40 10
30
20 1
10
0
0.00001 0.0001 0.001 0.01
VIN = 12V
VOUT = 3.3V 0.1
0.1 1 10
OUTPUT CURRENT (A)
FIGURE 13 CIRCUIT
3826 G01
Efficiency vs Output Current
100
VOUT = 3.3V
90
80
70
60
50
40
30
20
10
0
0.00001 0.0001 0.001 0.01
VIN = 12V
VIN = 5V
0.1 1 10
OUTPUT CURRENT (A)
FIGURE 13 CIRCUIT
3826 G02
Efficiency vs Input Voltage
98
96
94
92
90
88
86
84
82
0 5 10 15 20 25 30
INPUT VOLTAGE (V)
FIGURE 13 CIRCUIT
35 40
3826 G03
Load Step
(Burst Mode Operation)
VOUT
100mV/DIV
AC
COUPLED
IL
2A/DIV
20μs/DIV
FIGURE 13 CIRCUIT
VOUT = 3.3V
Load Step
(Forced Continuous Mode)
VOUT
100mV/DIV
AC
COUPLED
IL
2A/DIV
Load Step
(Pulse Skipping Mode)
VOUT
100mV/DIV
AC
COUPLED
IL
2A/DIV
3826 G04
20μs/DIV
FIGURE 13 CIRCUIT
VOUT = 3.3V
3826 G05
20μs/DIV
FIGURE 13 CIRCUIT
VOUT = 3.3V
3826 G06
Inductor Current at Light Load
FORCED
CONTINUOUS
MODE
2A/DIV
Burst Mode
OPERATION
PULSE
SKIPPING
MODE
2μs/DIV
FIGURE 13 CIRCUIT
VOUT = 3.3V
ILOAD = 100μA
3826 G07
Soft-Start-Up
VOUT2
2V/DIV
VOUT1
2V/DIV
20ms/DIV
FIGURE 13 CIRCUIT
3826 G08
Tracking Start-Up
VOUT2
2V/DIV
VOUT1
2V/DIV
20ms/DIV
FIGURE 13 CIRCUIT
3826 G09
3826fc
5
5 Page 
LTC3826
OPERATION (Refer to Functional Diagram)
Main Control Loop
The LTC3826 uses a constant frequency, current mode
wwws.dtaetpas-hdeoewt4nu.caormchitecture with the two controller channels
operating 180 degrees out of phase. During normal opera-
tion, each 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 left open or tied to a voltage less
than 4.7V, an internal 5.25V low dropout linear regulator
supplies INTVCC power from VIN. If EXTVCC is taken above
4.7V, the 5.25V regulator is turned off and a 7.5V low
dropout linear regulator is enabled that supplies INTVCC
power from EXTVCC. If EXTVCC is less than 7.5V (but
greater than 4.7V), the 7.5V regulator is in dropout and
INTVCC is approximately equal to EXTVCC. When EXTVCC
is greater than 7.5V (up to an absolute maximum rating
of 10V), INTVCC is regulated to 7.5V. Using the EXTVCC
pin allows the INTVCC power to be derived from a high
efficiency external source such as one of the LTC3826
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
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 (RUN1, RUN2 and TRACK/
SS1, TRACK/SS2 Pins)
The two channels of the LTC3826 can be independently
shut down using the RUN1 and RUN2 pins. Pulling either
of these pins below 0.7V shuts down the main control
loop for that controller. Pulling both pins low disables
both controllers and most internal circuits, including the
INTVCC regulator, and the LTC3826 draws only 4μA of
quiescent current.
Releasing either RUN pin allows an internal 0.5μA current
to pull up the pin and enable that controller. Alternatively,
the RUN pin may be externally pulled up or driven directly
by logic. Be careful not to exceed the Absolute Maximum
rating of 7V on this pin.
The start-up of each controller’s output voltage VOUT is
controlled by the voltage on the TRACK/SS1 and TRACK/
SS2 pin. When the voltage on the TRACK/SS pin is less
than the 0.8V internal reference, the LTC3826 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 1μA 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), 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. Typi-
cally, this requires connecting to the TRACK/SS pin an
3826fc
11
11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet LTC3826.PDF ] | |
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