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PDF LTC3708 Data sheet ( Hoja de datos )
| Número de pieza | LTC3708 | |
| Descripción | No RSENSE Low EMI / Synchronous DC/DC Controller with Output Tracking | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LTC3708 (archivo pdf) en la parte inferior de esta página. Total 30 Páginas | ||
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U.com Fast 2-Phase, NoLTRC3708SENSE
FEATURaEStaSheet4 DESCRIPTBIOuckOCutopnuttroTrllaecr kwinitgh■ Very Low Duty Factor Operation (tON(MIN) < 85ns)
.D■ No RSENSETM Option for Maximum Efficiency
w■ Very Fast Transient Response
w■ Programmable Output Voltage Up/Down Tracking
w■ 2-Phase Operation Reduces Input Capacitance
m■ 0.6V ±1% Output Voltage Reference
■ External Frequency Synchronization
o■ Monotonic Soft-Start
.c■ Onboard High Current MOSFET Drivers
■ Wide VIN Range: Up to 36V
■ Adjustable Cycle-by-Cycle Current Limit
U■ Instant Output Overvoltage Protection
t4■ Optional Short-Circuit Shutdown Timer
■ Power Good Output with 100µs Masking
e■ Available in 5mm × 5mm QFN Package
APPLICATIOUS he■ Digital Signal Processors
taS■ Network Servers
The LTC®3708 is a dual, 2-phase synchronous step-down
switching regulator with output voltage up/down tracking
capability. The IC allows either coincident or ratiometric
tracking. Multiple LTC3708s can be daisy-chained in
applications requiring more than two voltages to be tracked.
Power supply sequencing is accomplished using an exter-
nal soft-start timing capacitor.
The LTC3708 uses a constant on-time, valley current mode
control architecture to deliver very low duty factors with-
out requiring a sense resistor. Operating frequency is
selected by an external resistor and is compensated for
variations in input supply voltage. An internal phase-locked
loop allows the IC to be synchronized to an external clock.
Fault protection is provided by an output overvoltage
comparator and an optional short-circuit shutdown timer.
The regulator current limit level is user programmable. A
wide supply range allows voltages as high as 36V to be
stepped down to 0.6V output.
, LTC and LT are registered trademarks of Linear Technology Corporation.
No RSENSE is a trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATIO .DaHigh Efficiency Dual Output Step-Down Converter
VIN
5V 3.3V TO 28V
10µF
10Ω 1µF
4.7µF 100k
50V ×4
ww mVOUT1
2.5V
w o15A
POSCAP +
.c330µF
4V ×2
U12.1k
www.DataSheet4 16.04k
L1
1.4µH
B340A
19.1k
VIN
1.5M
6.04k
0.01µF
M1
0.22µF
M3
33k 10k
0.01µF
180pF 0.1µF
VCC DRVCC PGOOD
TG1 TG2
BOOST1
BOOST2
SW1
SENSE1+
SW2
SENSE2+
M2
0.22µF
BG1 LTC3708 BG2
SENSE1–
PGND1
SENSE2–
PGND2
M4
VFB1
TRACK2
ION1
ITH1
INTLPF
RUN/SS
SGND
VRNG1
VFB2
FCB
ION2
ITH2
EXTLPF
TRACK1
VRNG2
fIN
1k
100k
33k
0.1µF
25k 5V 180pF
L1: PANASONIC ETQP3HIR4BF
L2: PANASONIC ETQP2HIR2BF
M1, M2: RENESAS HAT2168
M3, M4: RENESAS HAT2165
L2
1.2µH
B340A
VOUT2
1.8V
+ POSCAP 15A
470µF
2.5V ×2
12.1k
1M
VIN
0.01µF
6.04k
3708 TA01
100
95
90
85
80
75
70
0.01
VOUT1 (0.5V/DIV)
VOUT2 (0.5V/DIV)
2ms/DIV
3708 TA01b
9.0
7.5
6.0
20VIN TO 2.5VOUT
5VIN TO 2.5VOUT
20VIN TO 1.8VOUT
5VIN TO 1.8VOUT
4.5
3.0
1.5
0.1 1
LOAD CURRENT (A)
0
10
3708 TA01c
3708f
1 page  
TYPICAL PERFOR A CE CHARACTERISTICS
LTC3708
Soft-Start (Figure 17 Circuit)
VOUT1
2V/DIV
VOUT2
2V/DIV
RUN/SS
5V/DIV
IL1
5A/DIV
Power Loss vs Input Voltage
6
IOUT = 15A
5
VOUT = 2.5V
4
3
VOUT = 1.8V
2
5ms/DIV
Power Loss vs Load Current
3.5
VIN = 5V
3.0
VOUT = 2.5V
2.5
VOUT = 1.8V
2.0
1.5
1.0
0.5
0
10 100 1000 10000 100000
LOAD (mA)
3707 G07
On-Time vs ION Current
10000
1000
100
10
1
10 100
ION CURRENT (µA)
1000
3708 G10
3708 G05
1
0
5
Frequency vs Input Voltage
260
240 IOUT = 15A
10 15
20
INPUT VOLTAGE (V)
25
3708 G06
Frequency vs Load Current
250
200
220
EXTERNAL SYNCHRONIZATION (ANY IOUT)
200 IOUT = 0A
180
160
5
10 15 20
INPUT VOLTAGE (V)
25
3708 G08
On-Time vs Temperature
300
ION = 30µA
250
200
150
ION = 60µA
100
50
0
–50 –25 0 25 50 75 100 125 150
TEMPERATURE (°C)
3708 G11
150
100
FORCED CONTINUOUS MODE
50 EXTERNAL
SYNCHRONIZATION
DISCONTINUOUS MODE
0
0 5 10 15
LOAD CURRENT (A)
3708 G09
Current Sense Threshold
vs ITH Voltage
300
VRNG =
250
200
150
100
2V
1.4V
1V
0.7V
50 0.5V
0
–50
–100
–150
–200
0
0.5 1 1.5
ITH VOLTAGE (V)
2 2.5
3708 G12
3708f
5
5 Page 
U
OPERATIO (Refer to Functional Diagram)
DRVCC
Power for the top and bottom MOSFET drivers is derived
from the DRVCC pin. The top MOSFET driver is powered
from a floating bootstrap capacitor CB. This capacitor is
normally recharged from DRVCC through an external Schot-
tky diode DB when the top MOSFET is turned off.
2-Phase Operation
For the LTC3708 to operate optimally as a 2-phase con-
troller, the resistors connected to the ION pins must be
selected such that the free-running frequency of each
channel is close to that of the other. An internal phase-
locked loop (PLL) will then ensure that channel 2 operates
at the same frequency as channel 1, but phase shifted by
180°. The loop filter connected to the INTLPF pin provides
stability to the PLL. For external clock synchronization, a
second PLL is incorporated to adjust the on-time of
channel 1 until its frequency is the same as the external
clock. Compensation for the external PLL is through the
EXTLPF pin.
The loop filter components tied to the INTLPF and EXTLPF
pins are used to compensate the internal PPL and external
PLL respectively. The typical value ranges are:
INTLPF: RIPLL = 2kΩ to 10kΩ, CIPLL = 10nF to 100nF
EXTLPF: REPLL ≤ 1kΩ, CEPLL = 10nF to 100nF
For noise suppression, a capacitor with a value of 1nF or
less should be placed from INTLPF to ground and EXTLPF
to ground.
LTC3708
The LTC3708’s 2-phase operation brings considerable
benefits to portable applications and automatic electron-
ics. It lowers the input filtering requirement, reduces
electromagnetic interference (EMI) and increases the power
conversion efficiency. Until the introduction of the 2-phase
operation, dual switching regulators operated both chan-
nels in phase (i.e., single phase operation). This means
that both controlling switches turned on at the same time,
causing current pulses of up to twice the amplitude of
those for one regulator to be drawn from the input capaci-
tor or battery. Such operation results in higher input RMS
current, larger and/or more expensive input capacitors,
more power loss and worse EMI in the input source
(whether a wall adapter or a battery).
In contrast to single phase operation, the two channels of
a 2-phase switching regulator are operated 180 degrees
out of phase. This effectively interleaves the current pulses
drawn by the switches, greatly reducing the overlap time
where they add together. The result is a significant reduc-
tion in total RMS input current, which in turn allows less
expensive input capacitors to be used, reduces shielding
requirements for EMI and improves real world operating
efficiency.
Figure 1 compares the input waveforms for a representa-
tive single phase dual switching regulator to the 2-phase
dual switching regulator. An actual measurement of the
RMS input current under these conditions shows that
5V SWITCH
20V/DIV
3.3V SWITCH
20V/DIV
INPUT CURRENT
5A/DIV
INPUT VOLTAGE
500mV/DIV
IIN(MEAS) = 2.53ARMS
(1a)
3708 F01a
IIN(MEAS) = 1.55ARMS
(1b)
3708 F01b
Figure 1. Input Waveforms Comparing Single Phase (1a) and 2-Phase (1b) Operation
for Dual Switching Regulators Converting 12V to 5V and 3.3V at 3A Each
3708f
11
11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet LTC3708.PDF ] | |
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