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PDF LTC3834 Data sheet ( Hoja de datos )
| Número de pieza | LTC3834 | |
| Descripción | Synchronous Step-Down Controller | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LTC3834 (archivo pdf) en la parte inferior de esta página. Total 28 Páginas | ||
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FEATURES
www.datasheet4u.com
n Wide Output Voltage Range: 0.8V ≤ VOUT ≤ 10V
n Low Operating Quiescent Current: 30μA
n OPTI-LOOP® Compensation Minimizes COUT
n ±1% Output Voltage Accuracy
n Wide VIN Range: 4V to 36V
n Phase-Lockable Fixed Frequency 140kHz to 650kHz
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 Clock Output for PolyPhase® Applications
n Output Overvoltage Protection
n Low Shutdown IQ: 4μA
n Internal LDO Powers Gate Drive from VIN or VOUT
n Selectable Continuous, Pulse Skipping or
Burst Mode® Operation at Light Loads
n Small 20-Lead TSSOP or 4mm × 5mm QFN Package
APPLICATIONS
n Automotive Systems
n Telecom Systems
n Battery-Operated Digital Devices
n Distributed DC Power Systems
LTC3834
30µA IQ Synchronous
Step-Down Controller
DESCRIPTION
The LTC®3834 is a high performance step-down switching
regulator controller that drives an all N-channel synchro-
nous power MOSFET stage. A constant-frequency current
mode architecture allows a phase-lockable frequency of
up to 650kHz.
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
LTC3834 features a precision 0.8V reference and a power
good output indicator. The 4V to 36V input supply range
encompasses a wide range of battery chemistries.
The TRACK/SS pin ramps the output voltage during
start-up. Current foldback limits MOSFET heat dissipa-
tion during short-circuit conditions. A reduced feature set
version of the part (LTC3834-1) is available in a smaller,
lower pin count package.
Comparison of LTC3834 and LTC3834-1
PART #
LTC3834
CLKOUT/
PHASMD
Yes
EXTVCC
Yes
PGOOD
Yes
PACKAGES
FE20/4mm × 5mm QFN
LTC3834-1 No No No GN16/3mm × 5mm DFN
L, LT, LTC, LTM, Burst Mode, PolyPhase 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 5408150, 5481178, 5705919, 5929620, 6304066,
6498466, 6580258, 6611131.
TYPICAL APPLICATION
High Efficiency Synchronous Step-Down Converter
0.01μF
560pF
54.2k
68.1k
215k
150pF
CLKOUT
PLLLPF
RUN
VIN
TG
PGOOD
TRACK/SS
BOOST
ITH
LTC3834
SW
SGND
PLLIN/MODE
VFB
SENSE–
SENSE+
INTVCC
EXTVCC
BG
PGND
0.22μF
4.7μF
VIN
4V TO 36V
10μF
3.3μH 0.012Ω
VOUT
3.3V
5A
150μF
3834 TA01
100
90
80
70
60
50
40
30
20
10
0
0.000001
0.0001
0.01
OUTPUT CURRENT (A)
10000
1000
100
10
1
0.1
1
3834 TA01b
3834fb
1
1 page  
LTC3834
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted.
Load Step (Burst Mode Operation)
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Load Step
(Forced Continuous Mode)
VOUT
100mV/DIV
AC
COUPLED
VOUT
100mV/DIV
AC
COUPLED
Load Step (Pulse Skipping Mode)
VOUT
100mV/DIV
AC
COUPLED
IL
2A/DIV
IL
2A/DIV
IL
2A/DIV
VOUT = 3.3V
20μs/DIV
FIGURE 11 CIRCUIT
3834 G04
VOUT = 3.3V
20μs/DIV
FIGURE 11 CIRCUIT
Inductor Current at Light Load
FORCED
CONTINUOUS
MODE
2A/DIV
Burst Mode
OPERATION
Soft Start-Up
VOUT
1V/DIV
3834 G05
VOUT = 3.3V
20μs/DIV
FIGURE 11 CIRCUIT
Tracking Start-Up
3834 G06
MASTER
2V/DIV
VOUT
2V/DIV
PULSE
SKIPPING
MODE
VOUT = 3.3V
2μs/DIV
ILOAD = 100μA
FIGURE 11 CIRCUIT
3834 G07
20ms/DIV
FIGURE 11 CIRCUIT
3834 G08
20ms/DIV
FIGURE 11 CIRCUIT
3834 G09
Total Input Supply Current vs
Input Voltage
350
FIGURE 11 CIRCUIT
300
250
200
150
300μA LOAD
100
50 NO LOAD
0
5 10 15 20 25 30 35
INPUT VOLTAGE (V)
3834 G10
EXTVCC Switchover and INTVCC
Voltages vs Temperature
6.0
5.8
5.6
5.4 INTVCC
5.2
5.0
4.8 EXTVCC RISING
4.6
4.4 EXTVCC FALLING
4.2
4.0
–45 –25 –5 15 35 55 75 95
TEMPERATURE (°C)
3834 G11
INTVCC Line Regulation
5.5
5.4
5.3
5.2
5.1
5.0
0
5 10 15 20 25 30 35 40
INPUT VOLTAGE (V)
3834 G12
3834fb
5
5 Page 
LTC3834
OPERATION (Refer to Functional Diagram)
When the RUN pin is pulled low to disable the LTC3834, or
when VIN drops below its undervoltage lockout threshold
wwwo.dfat3a.s7hVe,ett4hue.coTmRACK/SS pin is pulled low by an internal
MOSFET. When in undervoltage lockout, the controller is
disabled and the external MOSFETs are held off.
Light Load Current Operation (Burst Mode Operation,
Pulse-Skipping or Continuous Conduction)
(PLLIN/MODE Pin)
The LTC3834 can be enabled to enter high efficiency
Burst Mode operation, constant-frequency pulse-skipping
mode, or forced continuous conduction mode at low load
currents. To select Burst Mode operation, tie the PLLIN/
MODE pin to a DC voltage below 0.8V (e.g., SGND). To
select forced continuous operation, tie the PLLIN/MODE
pin to INTVCC. To select pulse skipping mode, tie the
PLLIN/MODE pin to a DC voltage greater than 0.8V and
less than INTVCC – 0.5V.
When the LTC3834 is enabled for Burst Mode operation,
the peak current in the inductor is set to approximately
one-tenth of the maximum sense voltage even though the
voltage on the ITH pin indicates a lower value. If the aver-
age inductor current is lower than the load current, the
error amplifier EA will decrease the voltage on the ITH pin.
When the ITH voltage drops below 0.4V, the internal sleep
signal goes high (enabling “sleep” mode) and both external
MOSFETs are turned off. The ITH pin is then disconnected
from the output of the EA and “parked” at 0.425V.
In sleep mode, much of the internal circuitry is turned off,
reducing the quiescent current that the LTC3834 draws to
only 30μA. In sleep mode, the load current is supplied by
the output capacitor. As the output voltage decreases, the
EA’s output begins to rise. When the output voltage drops
enough, the ITH pin is reconnected to the output of the
EA, the sleep signal goes low, and the controller resumes
normal operation by turning on the top external MOSFET
on the next cycle of the internal oscillator.
When the LTC3834 is enabled for Burst Mode operation,
the inductor current is not allowed to reverse. The reverse
current comparator (RICMP) turns off the bottom external
MOSFET just before the inductor current reaches zero,
preventing it from reversing and going negative, thus
operating in discontinuous operation.
In forced continuous operation, the inductor current is
allowed to reverse at light loads or under large transient
conditions. The peak inductor current is determined by the
voltage on the ITH pin, just as in normal operation. In this
mode, the efficiency at light loads is lower than in Burst
Mode operation. However, continuous operation has the
advantages of lower output ripple and less interference
to audio circuitry. In forced continuous mode, the output
ripple is independent of load current.
When the PLLIN/MODE pin is connected for pulse skip-
ping mode or clocked by an external clock source to
use the phase-locked loop (see Frequency Selection and
Phase-Locked Loop section), the LTC3834 operates in
PWM pulse skipping mode at light loads. In this mode,
constant-frequency operation is maintained down to ap-
proximately 1% of designed maximum output current.
At very light loads, the current comparator ICMP may
remain tripped for several cycles and force the external top
MOSFET to stay off for the same number of cycles (i.e.,
skipping pulses). The inductor current is not allowed to
reverse (discontinuous operation). This mode, like forced
continuous operation, exhibits low output ripple as well as
low audio noise and reduced RF interference as compared
to Burst Mode operation. It provides higher low current
efficiency than forced continuous mode, but not nearly as
high as Burst Mode operation.
3834fb
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11 Page | ||
| Páginas | Total 28 Páginas | |
| PDF Descargar | [ Datasheet LTC3834.PDF ] | |
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