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PDF LTC3814-5 Data sheet ( Hoja de datos )
| Número de pieza | LTC3814-5 | |
| Descripción | 60V Current Mode Synchronous Step-Up Controller | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC3814-5
60V Current Mode
Synchronous Step-Up Controller
FEATURES
■ High Output Voltages: Up to 60V
■ Large 1Ω Gate Drivers
■ No Current Sense Resistor Required
■ Dual N-Channel MOSFET Synchronous Drive
■ ±0.5% 0.8V Voltage Reference
■ Fast Transient Response
■ Programmable Soft-Start
■ Generates 5.5V Driver Supply
■ Power Good Output Voltage Monitor
■ Adjustable Off-Time/Frequency: tOFF(MIN) < 100ns
■ Adjustable Cycle-by-Cycle Current Limit
■ Undervoltage Lockout On Driver Supply
■ Output Overvoltage Protection
■ Thermally Enhanced 16-Pin TSSOP Package
APPLICATIONS
■ 24V Fan Supplies
■ 48V Telecom and Base Station Power Supplies
■ Networking Equipment, Servers
■ Automotive and Industrial Control Systems
DESCRIPTION
The LTC3814-5 is a synchronous step-up switching regula-
tor controller that can generate output voltages up to 60V.
The LTC3814-5 uses a constant off-time peak current
control architecture to deliver very high duty cycles with
accurate cycle-by-cycle current limit without requiring a
sense resistor.
A precise internal reference provides ±0.5% DC accuracy.
A high bandwidth (25MHz) error amplifier provides very
fast line and load transient response. Large 1Ω gate driv-
ers allow the LTC3814-5 to drive large power MOSFETs
for higher current applications. The operating frequency
is selected by an external resistor and is compensated for
variations in VIN. A shutdown pin allows the LTC3814-5 to
be turned off reducing the supply current to <230µA.
PARAMETER
Maximum VOUT
MOSFET Gate Drive
INTVCC UV+
INTVCC UV –
LTC3813
100V
6.35V to 14V
6.2V
6V
LTC3814-5
60V
4.5V to 14V
4.2V
4V
, 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, 5847554, 6304066, 6476589, 6580258, 6677210, 6774611.
TYPICAL APPLICATIONS
High Efficiency High Voltage Step-Up Converter
VOUT
PGOOD
263k
100k
1000pF
0.01µF
100k
100pF
ION NDRV
PGOOD
BOOST
LTC3814-5
VRNG
TG
VOFF
SW
RUN/SS
EXTVCC
INTVCC
ITH
BG
VFB SGND PGND
+
4.7µH
VIN
4.5V TO 14V
22µF
0.1µF
M1
Si7848DP
VOUT
24V
4A
D1
M2 MBR1100
Si7848DP
1µF
29.4k+
270µF
×2
1k
38145 TA01
Efficiency vs Load Current
100
VIN = 12V
95
90 VIN = 5V
85
80
0
1 2 34
LOAD (A)
38145 TA01b
38145f
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TYPICAL PERFORMANCE CHARACTERISTICS
LTC3814-5
Efficiency vs Load Current
100
VOUT = 50V
VIN = 36V
95 VIN = 24V
VIN = 12V
90
85
Frequency vs Input Voltage
300
FRONT PAGE CIRCUIT
280
ILOAD = 0A
260
ILOAD = 1A
240
220
Frequency vs Load Current
300
FRONT PAGE CIRCUIT
280
VIN = 12V
260
240
VIN = 5V
220
80
012345
LOAD (A)
38145 G04
ITH Voltage vs Load Current
3
FRONT PAGE CIRCUIT
VIN = 12V
VRNG = 1V
2
1
0
012345
LOAD CURRENT (A)
38145 G07
200
5
7 9 11 13 15
INPUT VOLTAGE (V)
38145 G05
Current Sense Threshold
vs ITH Voltage
400
VRNG = 2V
300
200 1.4V
1V
100 0.7V
0.5V
0
–100
–200
–300
–400
0 0.5 1 1.5 2
ITH VOLTAGE (V)
2.5 3
38145 G08
200
0
123
LOAD CURRENT (A)
4
38145 G06
Off-Time vs IOFF Current
10000
VOFF = INTVCC
1000
100
10
10
100 1000
IOFF CURRENT (µA)
10000
38145 G09
Off-Time vs Temperature
680
IOFF = 300µA
660
640
620
600
580
560
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
38145 G10
Maximum Current Sense
Threshold vs VRNG Voltage
400
300
200
100
0
0.5 1 1.5 2
VRNG VOLTAGE (V)
38145 G11
Maximum Current Sense
Threshold vs Temperature
240
VRNG = INTVCC
230
220
210
200
190
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
38145 G12
38145f
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LTC3814-5
OPERATION
IC/Driver Supply Power
The LTC3814-5’s internal control circuitry and top and bot-
tom MOSFET drivers operate from a supply voltage (INTVCC
pin) in the range of 4.5V to 14V. If the input supply voltage
or another available supply is within this voltage range it
can be used to supply IC/driver power. If a supply in this
range is not available, two internal regulators are available
to generate a 5.5V supply from the input or output. An
internal low dropout regulator is good for voltages up to
15V, and the second, a linear regulator controller, controls
the gate of an external NMOS to generate the 5.5V supply.
Since the NMOS is external, the user has the flexibility to
choose a BVDSS as high as necessary.
APPLICATIONS INFORMATION
The basic LTC3814-5 application circuit is shown on the
first page of this data sheet. External component selection
is primarily determined by the maximum input voltage and
load current and begins with the selection of the power
MOSFET switches. The LTC3814-5 uses the on-resistance
of the synchronous power MOSFET for determining the
inductor current. The desired amount of ripple current and
operating frequency largely determines the inductor value.
Next, COUT is selected for its ability to handle the large RMS
current and is chosen with low enough ESR to meet the
output voltage ripple and transient specification. Finally,
loop compensation components are selected to meet the
required transient/phase margin specifications.
Duty Cycle Considerations
For a boost converter, the duty cycle of the main switch
is:
D
=
1−
VIN
VOUT
; DMAX
=
1−
VIN(MIN)
VOUT
The maximum VOUT capability of the LTC3814-5 is inversely
proportional to the minimum desired operating frequency
and minimum off-time:
VOUT(MAX)
=
VIN(MIN)
f MIN• tOFF(MIN)
≤
60V
Maximum Sense Voltage and the VRNG Pin
The control circuit in the LTC3814-5 measures the input
current by using the RDS(ON) of the bottom MOSFET or
by using a sense resistor in the bottom MOSFET source,
so the output current needs to be reflected back to the
input in order to dimension the power MOSFET properly
and to choose the maximum sense voltage. Based on the
fact that, ideally, the output power is equal to the input
power, the maximum average input current and average
inductor current is:
IIN(MAX)
=
IL,AVG(MAX)
=
IO(MAX)
1− DMAX
The current mode control loop will not allow the induc-
tor peak to exceed VSENSE(MAX)/RSENSE. In practice, one
should allow some margin for variations in the LTC3814-
5 and external component values, and a good guide for
selecting the maximum sense voltage when VDS sensing
is used is:
VSENSE(MAX)
=
1.7
• RDS(ON) • IO(MAX)
1− DMAX
VSENSE is set by the voltage applied to the VRNG pin. Once
VSENSE is chosen, the required VRNG voltage is calculated
to be:
VRNG = 5.78 • (VSENSE(MAX) + 0.026)
An external resistive divider from INTVCC can be used
to set the voltage of the VRNG pin between 0.5V and 2V
resulting in nominal sense voltages of 60mV to 320mV.
Additionally, the VRNG pin can be tied to SGND or INTVCC
in which case the nominal sense voltage defaults to 95mV
or 215mV, respectively.
38145f
11
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| Páginas | Total 28 Páginas | |
| PDF Descargar | [ Datasheet LTC3814-5.PDF ] | |
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