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PDF LTC3609 Data sheet ( Hoja de datos )
| Número de pieza | LTC3609 | |
| Descripción | 6A Monolithic Synchronous Step-Down DC/DC Converter | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURES
n 6A Output Current
n Wide VIN Range = 4V to 32V (36V Maximum)
n Internal N-Channel MOSFETs
n True Current Mode Control
n Optimized for High Step-Down Ratios
n tON(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
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 7mm × 8mm 52-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.
LTC3609
32V, 6A Monolithic
Synchronous Step-Down
DC/DC Converter
DESCRIPTION
The LTC®3609 is a high efficiency, monolithic synchronous
step-down DC/DC converter that can deliver up to 6A output
current from a 4V to 32V (36V maximum) input supply. It
uses a valley current control architecture to deliver 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 LTC3609 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 LTC3609 is available in a
compact 7mm × 8mm QFN package.
TYPICAL APPLICATION
High Efficiency Step-Down Converter
0.1μF VOUT
100pF
1000pF
15.8k
VON
RUN/SS
ION
VIN
LTC3609
SW
ITH BOOST
187k
1.2μH
0.22μF
10μF
x3
VIN
4V TO 32V
100μF
x2
VOUT
2.5V
6A
SGND INTVCC
FCB
VRNG
PGOOD PGND
EXTVCC VFB
3609 TA01a
4.7μF
30.1k
9.53k
Efficiency and Power Loss vs
Load Current
100
90 EFFICIENCY
10000
80
1000
70
60
50 100
POWER LOSS
40
30
20
10 VOUT = 2.5V
EXTVCC = 5V
0
0.01 0.1
1
LOAD CURRENT (A)
10
VIN = 12V
VIN = 25V
1
10
3609 TA01b
3609f
1
1 page  
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TYPICAL PERFORMANCE CHARACTERISTICS
LTC3609
Efficiency vs Load Current
100
90
80
70
VOUT = 5V
VOUT = 3.3V
60 VOUT = 2.5V
50
VOUT = 1.8V
VOUT = 1.5V
40
VOUT = 1.2V
VOUT = 1V
30
20
10 VIN = 12V
FREQUENCY = 550kHz
0
0.01 0.1
1
LOAD CURRENT (A)
10
3609 G04
Efficiency vs Input Voltage
100
FCB = 5V
FIGURE 6 CIRCUIT
95
ILOAD = 6A
90
ILOAD = 1A
85
80
5
8 11 14 17 20 23 26 29 32
INPUT VOLTAGE (V)
3609 G05
Frequency vs Input Voltage
650
600
ILOAD = 6A
550
500
ILOAD = 1A
450
FCB = 0V
FIGURE 6 CIRCUIT
400
5 8 11 14 17 20 23 26
INPUT VOLTAGE (V)
29 32
3609 G06
Frequency vs Load Current
700
600 CONTINUOUS MODE
500
400
300
DISCONTINUOUS MODE
200
100
0
02468
LOAD CURRENT (A)
3609 G07
Load Regulation
0.80
FIGURE 6 CIRCUIT
0.60
0.40
0.20
0
–0.20
–0.40
–0.60
–0.80
0
246
LOAD CURRENT (A)
8
3609 G08
ITH Voltage vs Load Current
2.5
FIGURE 6 CIRCUIT
2.0
1.5
CONTINUOUS
MODE
1.0
0.5 DISCONTINUOUS
MODE
0
0246
LOAD CURRENT (A)
8
3609 G09
Load Current vs ITH Voltage at
Different VRNG
15
VRNG = 1.2V
10
5 VRNG = 0.7V
0 VRNG = 1V
–5
On-Time vs ION Current
10000
VVON = 0V
1000
100
–10
0
0.5 1.0 1.5
ITH VOLTAGE (V)
2.0 2.5
3609 G10
10
1
10
ION CURRENT (μA)
100
3609 G11
On-Time vs VON Voltage
1000
ION = 30μA
800
600
400
200
0
0 12
VON VOLTAGE (V)
3
3609 G12
3609f
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LTC3609
APPLICATIONS INFORMATION
The basic LTC3609 application circuit is shown on the
front page of this data sheet. External component selection
is primarily determined by the maximum load current.
The LTC3609 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 LTC3609 has an open-drain PGOOD output that
indicates when the output voltage is within ±10% of the
regulation point. The LTC3609 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 LTC3609 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 0.7V to 1.2V, 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 LTC3609 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.
3609f
11
11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet LTC3609.PDF ] | |
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