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PDF LTC3611 Data sheet ( Hoja de datos )
| Número de pieza | LTC3611 | |
| Descripción | 32V Monolithic Synchronous Step-Down DC/DC Converter | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURES
n 10A Output Current
n Wide VIN Range = 4.5V to 32V (36V Maximum)
n Internal N-Channel MOSFETs
n True Current Mode Control
n Optimized for High Step-Down Ratios
n t0N(MIN) ≤ 100ns
n Extremely Fast Transient Response
n Stable with Ceramic COUT
n ±1% 0.6V Voltage Reference
n Power Good Output Voltage Monitor
n Adjustable On-Time/Switching Frequency (>1MHz)
n Adjustable Current Limit
n Programmable Soft-Start
n Output Overvoltage Protection
n Optional Short-Circuit Shutdown Timer
n Low Shutdown IQ: 15μA
n Available in a 9mm × 9mm 64-Pin QFN Package
APPLICATIONS
n Point of Load Regulation
n Distributed Power Systems
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners. Protected by U.S. Patents including
5481178, 6100678, 6580258, 5847554, 6304066.
LTC3611
10A, 32V Monolithic
Synchronous Step-Down
DC/DC Converter
DESCRIPTION
The LTC®3611 is a high efficiency, monolithic synchronous
step-down DC/DC converter that can deliver up to 10A
output current from a 4.5V to 32V (36V maximum) input
supply. It uses a constant on-time valley current mode
control architecture to deliver very low duty cycle opera-
tion at high frequency with excellent transient response.
The operating frequency is selected by an external resistor
and is compensated for variations in VIN and VOUT.
The LTC3611 can be configured for discontinuous or
forced continuous operation at light load. Forced continu-
ous operation reduces noise and RF interference while
discontinuous mode provides high efficiency by reducing
switching losses at light loads.
Fault protection is provided by internal foldback current
limiting, an output overvoltage comparator and an optional
short-circuit shutdown timer. Soft-start capability for sup-
ply sequencing is accomplished using an external timing
capacitor. Theregulatorcurrentlimitisuserprogrammable.
A power good output voltage monitor indicates when
the output is in regulation. The LTC3611 is available in a
compact 9mm × 9mm QFN package.
TYPICAL APPLICATION
High Efficiency Step-Down Converter
0.1μF VOUT
100pF
680pF
12.5k
INTVCC
39.2k
11k
VON
RUN/SS
ION
VIN
LTC3611
SW
ITH BOOST
SGND INTVCC
FCB
VRNG
PGOOD PGND
EXTVCC VFB
3611 TA01a
182k
1μH
0.22μF
10μF
×3
VIN
4.5V TO 32V
100μF
×2
VOUT
2.5V
10A
4.7μF
30.1k
9.5k
Efficiency and Power Loss vs
Load Current
100
VOUT = 2.5V
90
80 VIN = 5V
70
VIN = 25V
10000
1000
60
50 100
POWER LOSS,
40 VIN = 5V
30
20 POWER LOSS,
10 VIN = 25V
10
0
0.01
0.1 1
LOAD CURRENT (A)
1
10
3611 TA01b
3611fb
1
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TYPICAL PERFORMANCE CHARACTERISTICS
LTC3611
Efficiency vs Load Current
100
DISCONTINUOUS
90
80
70
60
50
0.01
CONTINUOUS
VIN = 12V
VOUT = 2.5V
EXTVCC = 5V
FIGURE 6 CIRCUIT
0.1 1
LOAD CURRENT (A)
10
3611 G04
Efficiency vs Input Voltage
100
FCB = 5V
FIGURE 6 CIRCUIT
95
90
ILOAD = 10A
85
ILOAD = 1A
80
5
10 15 20 25 30 35
INPUT VOLTAGE (V)
3611 G05
Frequency vs Input Voltage
640
ILOAD = 10A
600
560
520
480 ILOAD = 0A
440
FCB = 0V
FIGURE 6 CIRCUIT
400
5 10 15
20
25
INPUT VOLTAGE (V)
30 35
3611 G06
Frequency vs Load Current
650
600
550 CONTINUOUS MODE
500
450
400 DISCONTINUOUS MODE
350
300
250
200
150
100
50
0
02 4 6 8
LOAD CURRENT (A)
10
3611 G07
Load Regulation
0.80 FIGURE 6 CIRCUIT
0.60
0.40
0.20
0
–0.20
–0.40
–0.60
–0.80
0
2 4 6 8 10
LOAD CURRENT (A)
3611 G08
Load Current vs ITH Voltage and
VRNG
25
20
VRNG = 1V
15
0.7V
10 0.5V
5
0
–5
–10
0 0.5 1 1.5 2 2.5 3
ITH VOLTAGE (V)
3611 G10
On-Time vs ION Current
10000
VVON = 0V
1000
100
10
1
10
ION CURRENT (μA)
100
3611 G11
ITH Voltage vs Load Current
2.5
FIGURE 6 CIRCUIT
2.0
1.5 CONTINUOUS
MODE
1.0
DISCONTINUOUS
MODE
0.5
0
0 5 10 15
LOAD CURRENT (A)
3611 G09
On-Time vs VON Voltage
1000
ION = 30μA
800
600
400
200
0
0 123
VON VOLTAGE (V)
3611 G12
3611fb
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LTC3611
APPLICATIONS INFORMATION
The basic LTC3611 application circuit is shown on the front
page of this data sheet. External component selection is
primarily determined by the maximum load current. The
LTC3611 uses the on-resistance of the synchronous power
MOSFET for determining the inductor current. The desired
amount of ripple current and operating frequency also
determines the inductor value. Finally, CIN is selected for its
ability to handle the large RMS current into the converter
and COUT is chosen with low enough ESR to meet the
output voltage ripple and transient specification.
VON and PGOOD
The LTC3611 has an open-drain PGOOD output that
indicates when the output voltage is within ±10% of the
regulation point. The LTC3611 also has a VON pin that
allows the on-time to be adjusted. Tying the VON pin high
results in lower values for RON which is useful in high VOUT
applications. The VON pin also provides a means to adjust
the on-time to maintain constant frequency operation in
applications where VOUT changes and to correct minor
frequency shifts with changes in load current.
VRNG Pin and ILIMIT Adjust
The VRNG pin is used to adjust the maximum inductor
valley current, which in turn determines the maximum
average output current that the LTC3611 can deliver. The
maximum output current is given by:
IOUT(MAX) = IVALLEY(MAX) + 1/2 ΔIL,
The IVALLEY(MAX) is shown in the figure “Maximum Valley
Current Limit vs VRNG Voltage” in the Typical Performance
Characteristics.
An external resistor divider from INTVCC can be used to
set the voltage on the VRNG pin from 1V to 1.4V, or it can
be simply tied to ground force a default value equivalent
to 0.7V. Do not float the VRNG pin.
Operating Frequency
The choice of operating frequency is a tradeoff between
efficiency and component size. Low frequency operation
improves efficiency by reducing MOSFET switching losses
but requires larger inductance and/or capacitance in order
to maintain low output ripple voltage.
The operating frequency of LTC3611 applications is de-
termined implicitly by the one-shot timer that controls the
on-time tON of the top MOSFET switch. The on-time is set
by the current into the ION pin and the voltage at the VON
pin according to:
tON
=
VVON
IION
(10pF)
Tying a resistor RON from VIN to the ION pin yields an
on-time inversely proportional to VIN. The current out of
the ION pin is:
IION
=
VIN
RON
For a step-down converter, this results in approximately
constant frequency operation as the input supply varies:
f=
VVON
VOUT
RON(10pF)
[Hz]
To hold frequency constant during output voltage changes,
tie the VON pin to VOUT or to a resistive divider from VOUT
when VOUT > 2.4V. The VON pin has internal clamps that
limit its input to the one-shot timer. If the pin is tied below
0.7V, the input to the one-shot is clamped at 0.7V. Similarly,
if the pin is tied above 2.4V, the input is clamped at 2.4V.
In high VOUT applications, tying VON to INTVCC so that
the comparator input is 2.4V results in a lower value for
RON. Figures 1a and 1b show how RON relates to switching
frequency for several common output voltages.
3611fb
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11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet LTC3611.PDF ] | |
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