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PDF LTC3703-5 Data sheet ( Hoja de datos )
| Número de pieza | LTC3703-5 | |
| Descripción | 60V Synchronous Switching Regulator Controller | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC3703-5www.DataSheet4U.com
60V Synchronous
Switching Regulator Controller
FEATURES
s High Voltage Operation: Up to 60V
s Large 1Ω Gate Drivers (with 5V Supply)
s No Current Sense Resistor Required
s Step-Up or Step-Down DC/DC Converter
s Dual N-Channel MOSFET Synchronous Drive
s Excellent Transient Response and DC Line Regulation
s Programmable Constant Frequency: 100kHz to
600kHz
s ±1% Reference Accuracy
s Synchronizable up to 600kHz
s Selectable Pulse Skip Mode Operation
s Low Shutdown Current: 25µA Typ
s Programmable Current Limit
s Undervoltage Lockout
s Programmable Soft-Start
s 16-Pin Narrow SSOP and 28-Pin SSOP Packages
U
APPLICATIO S
s 48V Telecom and Base Station Power Supplies
s Networking Equipment, Servers
s Automotive and Industrial Control
, LTC and LT are registered trademarks of Linear Technology Corporation.
*U.S. Patent Numbers: 5408150, 5055767, 6677210, 5847554, 5481178, 6304066, 6580258;
Others Pending.
DESCRIPTIO
The LTC®3703-5 is a synchronous step-down switching
regulator controller that can directly step-down voltages
from up to 60V, making it ideal for telecom and automotive
applications. The LTC3703-5 drives external logic level
N-channel MOSFETs using a constant frequency (up to
600kHz), voltage mode architecture.
A precise internal reference provides 1% DC accuracy. A
high bandwidth error amplifier and patented* line feed
forward compensation provide very fast line and load
transient response. Strong 1Ω gate drivers allow the
LTC3703-5 to drive multiple MOSFETs for higher current
applications. The operating frequency is user program-
mable from 100kHz to 600kHz and can also be synchro-
nized to an external clock for noise-sensitive applications.
Current limit is programmable with an external resistor
and utilizes the voltage drop across the synchronous
MOSFET to eliminate the need for a current sense resistor.
For applications requiring up to 100V operation, refer to
the LTC3703 data sheet.
PARAMETER
Maximum VIN
MOSFET Gate Drive
VCC UV+
VCC UV–
LTC3703-5
60V
4.5V to 15V
3.7V
3.1V
LTC3703
100V
9.3V to 15V
8.7V
6.2V
TYPICAL APPLICATIO
High Efficiency High Voltage Step-Down Converter
VCC
5V
1000pF
30k
10k
470pF
21.5k
1%
12k
100Ω
2200pF
113k
1%
0.1µF
MODE/SYNC VIN
FSET BOOST
COMP
TG
LTC3703-5
FB SW
IMAX
VCC
INV DRVCC
RUN/SS
BG
GND BGRTN
+
22µF
MMDL770T1
VIN
6V TO 60V
+
Si7850DP
22µF
×2
0.1µF
8µH
10Ω
10µF
1µF
Si7850DP
270µF +
16V
D1
MBR1100
VOUT
5V
5A
37035 TA04
Efficiency vs Load Current
100
VIN = 12V
95
VIN = 24V
VIN = 42V
90
85
80
0
1 2 34
LOAD CURRENT (A)
5
37053 TA04b
37035f
1
1 page  
TYPICAL PERFOR A CE CHARACTERISTICS
LTC3703-5www.DataSheet4U.com
Driver Peak Source Current
vs Temperature
1.2
VCC = 5V
1.1
1.0
0.9
0.8
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80 100
37035 G10
Driver Pull-Down RDS(ON)
vs Supply Voltage
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
2.5
5 7.5 10 12.5 15
DRVCC/BOOST VOLTAGE (V)
37035 G13
RUN/SS Pull-Up Current
vs VCC Voltage
5
4
3
2
1
0
0 2.5 5 7.5 10 12.5 15
VCC VOLTAGE (V)
37035 G16
Driver Pull-Down RDS(ON)
vs Temperature
1.6
VCC = 5V
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80 100
37035 G11
Rise/Fall Time
vs Gate Capacitance
200
VCC = 5V
150
RISE TIME
100
50
FALL TIME
0
0 5 10 15 20
GATE CAPACITANCE (nF)
37035 G14
RUN/SS Sink Current
vs SW Voltage
25
IMAX = 0.3V
20
15
10
5
0
–5
–10
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
|SW| VOLTAGE (V)
37035 G17
Driver Peak Source Current
vs Supply Voltage
3.0
2.5
2.0
1.5
1.0
0.5
0
0 2.5 5 7.5 10 12.5 15
DRVCC/BOOST VOLTAGE (V)
37035 G12
RUN/SS Pull-Up Current
vs Temperature
5
VCC = 5V
4
3
2
1
0
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80 100
15735 G15
Max % DC vs RUN/SS Voltage
100
90
80
70
60
50
40
30
20
10
0
–10
0.5
1.0 1.5 2.0 2.5
RUN VOLTAGE (V)
3.0
37035 G18
37035f
5
5 Page 
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OPERATIO (Refer to Functional Diagram)
For maximum protection, the LTC3703-5 current limit
consists of a steady-state limit circuit and an instanta-
neous limit circuit. The steady-state limit circuit is a gm
amplifier that pulls a current from the RUN/SS pin propor-
tional to the difference between the SW and IMAX voltages.
This current begins to discharge the capacitor at RUN/SS,
reducing the duty cycle and controlling the output voltage
until the current regulates at the limit. Depending on the
size of the capacitor, it may take many cycles to discharge
the RUN/SS voltage enough to properly regulate the
output current. This is where the instantaneous limit
circuit comes into play. The instantaneous limit circuit is
a cycle-by-cycle comparator which monitors the bottom
MOSFET’s drain voltage and keeps the top MOSFET from
turning on whenever the drain voltage is 50mV above the
programmed max drain voltage. Thus the cycle-by-cycle
comparator will keep the inductor current under control
until the gm amplifier gains control.
Pulse Skip Mode
The LTC3703-5 can operate in one of two modes select-
able with the MODE/SYNC pin—Pulse Skip Mode or
forced continuous mode. Pulse Skip Mode is selected
when increased efficiency at light loads is desired. In this
mode, the bottom MOSFET is turned off when inductor
current reverses to minimize the efficiency loss due to
reverse current flow. As the load is decreased (see Fig-
ure␣ 5), the duty cycle is reduced to maintain regulation
until its minimum on-time (~200ns) is reached. When the
load decreases below this point, the LTC3703-5 begins to
LTC3703-5www.DataSheet4U.com
skip cycles to maintain regulation. The frequency drops
but this further improves efficiency by minimizing gate
charge losses. In forced continuous mode, the bottom
MOSFET is always on when the top MOSFET is off,
allowing the inductor current to reverse at low currents.
This mode is less efficient due to resistive losses, but has
the advantage of better transient response at low currents,
constant frequency operation, and the ability to maintain
regulation when sinking current. See Figure 4 for a com-
parison of the effect on efficiency at light loads for each
mode. The MODE/SYNC threshold is 0.8V ±7.5%, allow-
ing the MODE/SYNC to act as a feedback pin for regulating
a second winding. If the feedback voltage drops below
0.8V, the LTC3703-5 reverts to continuous operation to
maintain regulation in the secondary supply.
100
VIN = 12V
90
VIN = 42V
80
70
60
50
VIN = 12V
40
VIN = 42V
30
20
10
0
10
VOUT = 5V
FORCED CONTINUOUS
PULSE SKIP MODE
100 1000
LOAD (mA)
10000
37035 F04
Figure 4. Efficiency in Pulse Skip/Forced Continuous Modes
PULSE SKIP MODE
FORCED CONTINUOUS
DECREASING
LOAD
CURRENT
37035 F05
Figure 5. Comparison of Inductor Current Waveforms for Pulse Skip Mode and Forced Continuous Operation
37035f
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11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet LTC3703-5.PDF ] | |
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