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PDF LTC3713 Data sheet ( Hoja de datos )
| Número de pieza | LTC3713 | |
| Descripción | Low Input Voltage / High Power / No RSENSE Synchronous Buck DC/DC Controller | |
| Fabricantes | Linear | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LTC3713 (archivo pdf) en la parte inferior de esta página. Total 24 Páginas | ||
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LTC3713
Low Input Voltage,
High Power, No RSENSETM
Synchronous Buck DC/DC Controller
FEATURES
s Very Low VIN(MIN): 1.5V
s True Current Mode Control
s 5V Drive for N-Channel MOSFETs Eliminates
Auxillary 5V Supply
s No Sense Resistor Required
s Uses Standard 5V Logic-Level N-Channel MOSFETs
s Adjustable Current Limit
s Adjustable Frequency
s Switch tON(MIN) < 100ns
s 2% to 90% Duty Cycle at 200kHz
s 0.8V ±1% Reference
s Power Good Output Voltage Monitor
s Programmable Soft-Start
s Output Overvoltage Protection
s Optional Short-Circuit Shutdown Timer
s Small 24-Lead SSOP Package
U
APPLICATIO S
s Telecom Card 3.3V, 2.5V, 1.8V Step-Down
s Bus Termination (DDR memory, SSTL)
s Synchronous Buck with General Purpose Boost
s Low VIN Synchronous Boost
DESCRIPTIO
The LTC®3713 is a high current, high efficiency synchro-
nous buck switching regulator controller optimized for
use with very low input supply voltages. It operates from
inputs as low as 1.5V and provides a regulated output
voltage from 0.8V up to (0.9)VIN. The controller uses
a valley current control architecture to enable high operat-
ing frequencies without requiring a sense resistor.
Operating frequency is selected by an external resistor and
is compensated for variations in VIN and VOUT. The LTC3713
uses a pair of standard 5V logic-level N-channel external
MOSFETs, eliminating the need for expensive P-channel
or low threshold devices.
Discontinuous mode operation provides high efficiency
operation at light loads. A forced continuous control
pin reduces noise and RF interference, and can assist
secondary winding regulation by disabling discontinuous
operation when the main output is lightly loaded. Fault
protection is provided by internal foldback current limit-
ing, an output overvoltage comparator and an optional
short-circuit shutdown timer.
, LTC and LT are registered trademarks of Linear Technology Corporation.
No RSENSE is a trademark of Linear Technology Corporation.
TYPICAL APPLICATIO
330k
5.6k
10k
680pF
20k
0.1µF
SHDN BOOST
ION TG
LTC3713
VFB1
SW1
SENSE+
BG
ITH PGND
SENSE–
RUN/SS INTVCC
PGOOD
VIN1
SGND
VIN2
12.1k
VFB2
SW2
CMDSH-3
0.33µF
M1
10µF
M2
22µF
×2
VIN
1.8V TO 3.3V
L1
1.8µH
+
B340A
COUT
270µF
×2
VOUT
1.25V
10A
4.7µF
37.4k
3713 F01a
MBR0520
4.7µH
COUT: PANASONIC EEFUEOD271R
L1: (A) PANASONIC ETQP6FIR8BFA
(B) TOKO D104C-1.8µH
M1, M2: (A) IRF7822, (B) IRF7811A
Figure 1. High Efficiency Step-Down Converter from 1.8V to 3.3V Input
Efficiency vs Load Current
100
VIN = 2.5V
90
A
80
B
70
60
50
40
30
20
10
0
0.01 0.04 0.10 0.40 1 3 7
LOAD CURRENT (A)
12 15
3713 F01b
3713fa
1
1 page  
TYPICAL PERFOR A CE CHARACTERISTICS
Load Regulation
0
–0.1
–0.2
–0.3
–0.4
–0.5
–0.6
FIGURE 1 CIRCUIT
–0.7
0 1 2 3 4 5 6 7 8 9 10
LOAD CURRENT (A)
3713 G11
On-Time vs VON Voltage
1000
IION = 30µA
800
600
400
200
0
0 123
VON VOLTAGE (V)
3713 G14
Maximum Current Sense
Threshold vs VRNG Voltage
300
250
200
150
100
50
0
0.5 0.75 1.0 1.25 1.5
VRNG VOLTAGE (V)
1.75 2.0
3713 G17
Frequency vs Input Voltage
350
300
LOAD = 6A
250
200
LOAD = 0A
150
100
50
0
1.5 2.0
FIGURE 1 CIRCUIT
2.5 3.0 3.5 4.0
INPUT VOLTAGE (V)
4.5 5.0
3713 G12
On-Time vs Temperature
300
IION = 30µA
250
200
150
100
50
0
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3713 G15
Maximum Current Sense
Threshold vs RUN/SS Voltage
150
VRNG = 1V
125
100
75
50
25
0
1.5
2 2.5 3
RUN/SS VOLTAGE (V)
3.5
3713 G18
LTC3713
On-Time vs ION Current
10k
VVON = 0V
1k
100
10
1
10
ION CURRENT (µA)
Current Limit Foldback
150
VRNG = 1V
125
100
3713 G13
100
75
50
25
0
0 0.2 0.4 0.6 0.8
VFB (V)
3713 G16
Maximum Current Sense
Threshold vs Temperature
150
VRNG = 1V
140
130
120
110
100
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3713 G19
3713fa
5
5 Page 
LTC3713
APPLICATIO S I FOR
SENSE+
WITHOUT
RSENSE
ATIO
SENSE+
SENSE–
VOUT
ROS2
+ VOS –
ROS1
RSENSE
3713 F02
Figure 2. Sense Voltage Offset
range with respect to zero current. This can be accom-
plished by introducing an offset into the sense voltage as
shown in Figure 2.
The first step in calculating the amount of required offset
voltage is to determine the maximum sense voltage.
VSENSE = IOUT(MAX) • RSENSE
A good rule of thumb is to set the maximum sense voltage
for a current limit that is 30% greater than the maximum
source current.
The voltage on pin VRNG should be set based on the value
of VSENSE.
VRNG = VSENSE/0.133
VOS can be calculated using the following formula:
VOS = 0.6VSENSE
The offset voltage is added as shown in Figure 2 and can
be set by choosing the values of ROS1 and ROS2:
VOS
=
VOUT • ROS1
ROS1 + ROS2
The offset voltage must be scaled to VOUT to avoid inter-
fering with the internal current limit foldback.
Power MOSFET Selection
The LTC3713 requires two external N-channel power
MOSFETs, one for the top (main) switch and one for the
bottom (synchronous) switch. Important parameters for
the power MOSFETs are the breakdown voltage V(BR)DSS,
threshold voltage V(GS)TH, on-resistance RDS(ON), reverse
transfer capacitance CRSS and maximum current IDS(MAX).
The gate drive voltage is set by the 5V INTVCC supply.
Consequently, logic-level threshold MOSFETs must be
used in LTC3713 applications.
When the bottom MOSFET is used as the current sense
element, particular attention must be paid to its
on-resistance. MOSFET on-resistance is typically speci-
fied with a maximum value RDS(ON)(MAX) at 25°C. In this
case, additional margin is required to accommodate the
rise in MOSFET on-resistance with temperature:
RDS(ON)(MAX)
=
RSENSE
ρT
The ρT term is a normalization factor (unity at 25°C)
accounting for the significant variation in on-resistance
with temperature, typically about 0.4%/°C as shown in
Figure 3. For a maximum junction temperature of 100°C,
using a value ρT = 1.3 is reasonable.
2.0
1.5
1.0
0.5
0
– 50
0 50 100
JUNCTION TEMPERATURE (°C)
150
3713 F03
Figure 3. RDS(ON) vs Temperature
The power dissipated by the top and bottom MOSFETs
strongly depends upon their respective duty cycles and
the load current. When the LTC3713 is operating in
continuous mode, the duty cycles for the MOSFETs are:
DTOP
=
VOUT
VIN
DBOT
=
VIN
– VOUT
VIN
3713fa
11
11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet LTC3713.PDF ] | |
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