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PDF LTC3610 Data sheet ( Hoja de datos )
| Número de pieza | LTC3610 | |
| Descripción | 12A Monolithic Synchronous Step-Down DC/DC Converter | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURES
■ 12A Output Current
■ Wide VIN Range = 4V to 24V
■ Internal N-Channel MOSFETs
■ True Current Mode Control
■ Optimized for High Step-Down Ratios
■ tON(MIN) ≤100ns
■ Extremely Fast Transient Response
■ Stable with Ceramic COUT
■ ±1% 0.6V Voltage Reference
■ Power Good Output Voltage Monitor
■ Adjustable On-Time/Switching Frequency
■ Adjustable Current Limit
■ Programmable Soft-Start
■ Output Overvoltage Protection
■ Optional Short-Circuit Shutdown Timer
■ Low Shutdown IQ: 15μA
■ Available in a 9mm × 9mm 64-Pin QFN Package
APPLICATIONS
■ Point of Load Regulation
■ 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.
LTC3610
24V, 12A Monolithic
Synchronous Step-Down
DC/DC Converter
DESCRIPTION
The LTC®3610 is a high efficiency, monolithic synchronous
step-down DC/DC converter that can deliver up to 12A
output current from a 4V to 24V (28V maximum) input
supply. It uses a valley current control architecture to de-
liver very low duty cycle operation 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 LTC3610 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. The regulator current limit is user programmable.
A power good output voltage monitor indicates when
the output is in regulation. The LTC3610 is available in a
compact 9mm × 9mm QFN package.
TYPICAL APPLICATION
High Efficiency Step-Down Converter
0.1μF
100pF
470pF
31.83k
VON
RUN/SS
ION
VIN
LTC3610
SW
ITH BOOST
SGND INTVCC
FCB
VRNG
PGOOD PGND
EXTVCC VFB
3610 TA01a
604k
0.47μH
0.22μF
10μF
×3
VIN
4V TO 24V
100μF
×2
VOUT
2.5V
12A
4.7μF
30.1k
9.5k
Efficiency vs Load Current
100
95
90
85
80
75
70
65
60
55
50
0.01
VIN = 5V
VIN = 12V
10000
1000
100
POWER LOSS 12V
POWER LOSS 5V
10
VOUT = 2.5V
1
0.1 1 10
LOAD CURRENT (A)
3610 TA01b
3610fd
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TYPICAL PERFORMANCE CHARACTERISTICS
LTC3610
Transient Response
Transient Response
(Discontinuous Mode)
Start-Up
VOUT
100mV/DIV
IL
5A/DIV
ILOAD
5A/DIV
40μs/DIV
LOAD STEP 0A TO 8A
VIN = 12V
VOUT = 2.5V
FCB = 0V
FIGURE 6 CIRCUIT
VOUT
100mV/DIV
3610 G01
IL
5A/DIV
ILOAD
5A/DIV
40μs/DIV
ILOAD = 1A TO 7A
VIN = 12V
VOUT = 2.5V
FCB = INTVCC
FIGURE 6 CIRCUIT
RUN/SS
2V/DIV
3610 G02
VOUT
1V/DIV
IL
5A/DIV
40ms/DIV
VIN = 12V
VOUT = 2.5V
RLOAD = 0.5Ω
FIGURE 6 CIRCUIT
3610 G03
Efficiency vs Load Current
100
DISCONTINUOUS
MODE
90
80
CONTINUOUS
MODE
70
60
50
0.001
VIN = 12V
VOUT = 2.5V
EXTVCC = 5V
FIGURE 6 CIRCUIT
0.01 0.1
1
LOAD CURRENT (A)
10
3610 G04
Efficiency vs Input Voltage
100
FCB = 5V
FIGURE 6 CIRCUIT
95
ILOAD = 10A
90
ILOAD = 1A
85
80
5
10 15 20
INPUT VOLTAGE (V)
25
3610 G05
Frequency vs Input Voltage
640
ILOAD = 10A
600
560
520
ILOAD = 0A
480
440
FCB = 0V
FIGURE 6 CIRCUIT
400
5 10
15
20
INPUT VOLTAGE (V)
25
3610 G06
Frequency vs Load Current
650
600
550 CONTINUOUS MODE
500
450
400
350
300 DISCONTINUOUS MODE
250
200
150
100
50
0
0 2 4 6 8 10 12
LOAD CURRENT (A)
3610 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 12
LOAD CURRENT (A)
3610 G08
ITH Voltage vs Load Current
2.5
FIGURE 6 CIRCUIT
2.0
1.5
CONTINUOUS
MODE
1.0
DISCONTINUOUS
0.5 MODE
0
0 3 6 9 12
LOAD CURRENT (A)
3610 G09
3610fd
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LTC3610
APPLICATIONS INFORMATION
The basic LTC3610 application circuit is shown on the
front page of this data sheet. External component selection
is primarily determined by the maximum load current.
The LTC3610 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 LTC3610 has an open-drain PGOOD output that
indicates when the output voltage is within ±10% of the
regulation point. The LTC3610 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 LTC3610 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 0.5V to 1V, or it can
be simply tied to ground force a default value equivalent
to 0.7V. When setting current limit, ensure that the junc-
tion temperature does not exceed the maximum rating of
125°C. 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 LTC3610 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 (10pF)
IION
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.
3610fd
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11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet LTC3610.PDF ] | |
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