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PDF LTC3834-1 Data sheet ( Hoja de datos )
| Número de pieza | LTC3834-1 | |
| Descripción | Synchronous Step-Down Controller | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC3834-1
30μA IQ Synchronous
Step-Down Controller
FEATURES
www.datasheet4u.com
■ Wide Output Voltage Range: 0.8V V OUT 10V
■ Low Operating IQ: 30μA
■ OPTI-LOOP® Compensation Minimizes COUT
■ ±1% Output Voltage Accuracy
■ Wide VIN Range: 4V to 36V
■ Phase-Lockable Fixed Frequency 140kHz to 650kHz
■ Dual N-Channel MOSFET Synchronous Drive
■ Very Low Dropout Operation: 99% Duty Cycle
■ Adjustable Output Voltage Soft-Start or Tracking
■ Output Current Foldback Limiting
■ Output Overvoltage Protection
■ Low Shutdown IQ: 4μA
■ Selectable Continuous, Pulse-Skipping or
Burst Mode® Operation at Light Loads
■ Small 16-Lead Narrow SSOP or 5mm × 3mm
DFN Package
U
APPLICATIO S
■ Automotive Systems
■ Telecom Systems
■ Battery-Operated Digital Devices
■ Distributed DC Power Systems
DESCRIPTIO
The LTC®3834-1 is a high performance step-down switch-
ing regulator controller that drives an all N-channel syn-
chronous power MOSFET stage. A constant-frequency
current mode architecture allows a phase-lockable fre-
quency of up to 650kHz.
The 30μA no-load quiescent current extends operating
life in battery powered systems. OPTI-LOOP compen-
sation allows the transient response to be optimized over
a wide range of output capacitance and ESR values. The
LTC3834-1 features a precision 0.8V reference . The 4V to
36V input supply range encompasses a wide range of bat-
tery chemistries.
The TRACK/SS pin ramps the output voltage during start-
up. Current foldback limits MOSFET heat dissipation
during short-circuit conditions. An enhanced feature set
part (LTC3834) is available.
Comparison of LTC3834 and LTC3834-1
PART #
LTC3834
CLKOUT/
PHASMD
YES
EXTVCC
YES
PGOOD
YES
LTC3834-1
NO
NO
NO
PACKAGES
FE20/4 × 5 QFN
GN16/3 × 5 DFN
, 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 APPLICATIO
High Efficiency Step-Down Converter
0.01μF
560pF
54.2k
68.1k
215k
PLLLPF
VIN
RUN TG
TRACK/SS
BOOST
ITH
LTC3834-1
SW
150pF
SGND
PLLIN/MODE
VFB
SENSE–
SENSE+
INTVCC
BG
PGND
0.22μF
10μF
3.3μH 0.012Ω
4.7μF
VIN
4V TO 36V
VOUT
3.3V
5A
150μF
38341 TA01
Efficiency and Power Loss
vs Load Current
100 10000
90
80 1000
70
60 100
50
40 10
30
20 1
10
0
0.000001
0.0001
0.01
OUTPUT CURRENT (A)
0.1
1
38341 TA01b
38341f
1
1 page  
LTC3834-1
TYPICAL PERFOR A CE CHARACTERISTICS TA = 25ºC, unless otherwise noted.
Total Input Supply Current vs
Input Voltage
www.da3t5a0sheet4u.com
FIGURE 10 CIRCUIT
300
250
200
150
300μA LOAD
100
50 NO LOAD
0
5 10 15 20 25 30 35
INPUT VOLTAGE (V)
38341 G10
Maximum Current Sense Voltage
vs ITH Voltage Cycle
100
FORCED CONTINUOUS
80
Burst Mode OPERATION
(RISING)
Burst Mode OPERATION
6O (FALLING)
PULSE SKIPPING
40
20
0
–20
–40
0
10% DUTY CYCLE
0.2 0.4 0.6 0.8 1.0 1.2 1.4
ITH PIN VOLTAGE (V)
38341 G13
INTVCC Voltages vs Temperature
6.0
5.8
5.6
5.4 INTVCC
5.2
5.0
4.8
4.6
4.4
4.2
4.0
–45 –25 –5 15 35 55 75 95
TEMPERATURE (°C)
38341 G11
SENSE Pins Total Input Bias
Current
60
30
0
–30
–60
–90
–120
–150
–180
–210
–240
–270
–300
0 1 2 3 4 5 6 7 8 9 10
VSENSE COMMON MODE VOLTAGE (V)
38341 G14
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)
38341 G12
Maximum Current Sense
Threshold vs Duty
120
100
80
60
40
20
0
0 10 20 30 40 50 60 70 80 90 100
DUTY CYCLE (%)
38341 G15
Foldback Current Limit
120
100
80
60
40
20
0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
FEEDBACK VOLTAGE (V)
38341 G16
Quiescent Current vs Temperature
40
38
36
34
32
30
28
26
24
22
–45 –30 –15 0 15 30 45 60 75 90
TEMPERATURE (°C)
38341zz G17
38341f
5
5 Page 
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OPERATIO (Refer to Functional Diagram)
The typical capture range of the LTC3834-1’s phase-
locked loop is from approximately 115kHz to 800kHz,
wwww.diatthasahegeut4aur.caonmtee to be between 140kHz and 650kHz. In
other words, the LTC3834-1’s PLL is guaranteed to lock to
an external clock source whose frequency is between
140kHz and 650kHz.
The typical input clock thresholds on the PLLIN/MODE pin
are 1.6V (rising) and 1.2V (falling).
LTC3834-1
Output Overvoltage Protection
An overvoltage comparator guards against transient over-
shoots as well as other more serious conditions that
may overvoltage the output. When the VFB pin rises to
more than 10% higher than its regulation point of
0.800V, the top MOSFET is turned off and the bottom
MOSFET is turned on until the overvoltage condition
is cleared.
APPLICATIO S I FOR ATIO
RSENSE Selection for Output Current
RSENSE is chosen based on the required output current.
The current comparator has a maximum threshold of
100mV/RSENSE and an input common mode range of
SGND to 10V. The current comparator threshold sets the
peak of the inductor current, yielding a maximum average
output current IMAX equal to the peak value less half the
peak-to-peak ripple current, I L.
Allowing a margin for variations in the IC and external
component values yields:
RSENSE
=
80mV
IMAX
When using the controller in very low dropout conditions,
the maximum output current level will be reduced due to
the internal compensation required to meet stability crite-
rion for buck regulators operating at greater than 50%
duty factor. A curve is provided to estimate this reduction
in peak output current level depending upon the operating
duty factor.
Operating Frequency and Synchronization
The choice of operating frequency, is a trade-off between
efficiency and component size. Low frequency operation
improves efficiency by reducing MOSFET switching losses,
both gate charge loss and transition loss. However, lower
frequency operation requires more inductance for a given
amount of ripple current.
The internal oscillator of the LTC3834-1 runs at a nominal
400kHz frequency when the PLLLPF pin is left floating and
the PLLIN/MODE pin is a DC low or high. Pulling the
PLLLPF to INTVCC selects 530kHz operation; pulling the
PLLLPF to SGND selects 250kHz operation.
Alternatively, the LTC3834-1 will phase-lock to a clock
signal applied to the PLLIN/MODE pin with a frequency
between 140kHz and 650kHz (see Phase-Locked Loop
and Frequency Synchronization).
Inductor Value Calculation
The operating frequency and inductor selection are inter-
related in that higher operating frequencies allow the use
of smaller inductor and capacitor values. So why would
anyone ever choose to operate at lower frequencies with
larger components? The answer is efficiency. A higher
frequency generally results in lower efficiency because of
MOSFET gate charge losses. In addition to this basic
trade-off, the effect of inductor value on ripple current and
low current operation must also be considered.
The inductor value has a direct effect on ripple current.
The inductor ripple current I L decreases with higher
inductance or frequency and increases with higher VIN:
ΔIL
=
1
(f)(L)
⎛
VOUT ⎝⎜ 1–
VOUT
VIN
⎞
⎠⎟
38341f
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11 Page | ||
| Páginas | Total 28 Páginas | |
| PDF Descargar | [ Datasheet LTC3834-1.PDF ] | |
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