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PDF LTC3722-1 Data sheet ( Hoja de datos )
| Número de pieza | LTC3722-1 | |
| Descripción | Synchronous Dual Mode Phase Modulated Full Bridge Controllers | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURES
n Adaptive or Manual Delay Control for Zero Voltage
Switching Operation
n Adjustable Synchronous Rectification Timing for
Highest Efficiency
n Adjustable Maximum ZVS Delay
n Adjustable System Undervoltage Lockout Hysteresis
n Programmable Leading Edge Blanking
n Very Low Start-Up and Quiescent Currents
n Current Mode (LTC3722-1) or Voltage Mode
(LTC3722-2) Operation
n Programmable Slope Compensation
n VCC UVLO and 25mA Shunt Regulator
n 50mA Output Drivers
n Soft-Start, Cycle-by-Cycle Current Limiting and
Hiccup Mode Short-Circuit Protection
n 5V, 15mA Low Dropout Regulator
n 24-Pin Surface Mount GN Package
APPLICATIONS
n Telecommunications, Infrastructure Power Systems
n Distributed Power Architectures
n Server Power Supplies
LTC3722-1/LTC3722-2
Synchronous Dual Mode
Phase Modulated
Full Bridge Controllers
DESCRIPTION
The LTC®3722-1/LTC3722-2 phase-shift PWM controllers
provide all of the control and protection functions neces-
sary to implement a high efficiency, zero voltage switched
(ZVS), full bridge power converter. Adaptive ZVS circuitry
delays the turn-on signals for each MOSFET independent
of internal and external component tolerances. Manual
delay set mode enables secondary side control operation
or direct control of switch turn-on delays.
The LTC3722-1/LTC3722-2 feature adjustable synchron-
ous rectifier timing for optimal efficiency. A UVLO program
input provides accurate system turn-on and turn-off
voltages. The LTC3722-1 features peak current mode
control with programmable slope compensation and
leading edge blanking, while the LTC3722-2 employs
voltage mode control.
The LTC3722-1/LTC3722-2 feature extremely low operating
and start-up currents. Both devices include a full range of
protection features and are available in the 24-pin surface
mount GN package.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
DirectSense is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners.
TYPICAL APPLICATION
VIN
36V TO
72V
CIN
R1
U1 U2
MA MC
T1
LTC3722
MB MD
L1
L2
RCS
T2
C1
U1, U2: LTC4440 GATE DRIVER
U3: LTC3901 GATE DRIVER
ME
U3 MF
372212 TA01a
VOUT
12V
COUT
12VOUT, 240W Converter Efficiency
95
36VIN
90
48VIN
72VIN
85
80
75
0 2 4 6 8 10 12 14 16 18 20
CURRENT (A)
372212 TA01b
For more information www.linear.com/LTC3722
372212fb
1
1 page  
LTC3722-1/LTC3722-2
TYPICAL PERFORMANCE CHARACTERISTICS
Start-Up ICC vs VCC
200
TA = 25°C
150
100
50
VCC vs ISHUNT
10.50
TA = 25°C
10.25
10.00
9.75
Oscillator Frequency
vs Temperature
260 CT = 270pF
250
240
0
0 2 4 6 8 10
VCC (V)
372212 G01
Leading Edge Blanking Time
vs RLEB
350
TA = 25°C
300
250
200
150
100
50
0
0 10 20 30 40 50 60 70 80 90 100
RLEB (k)
372212 G04
Error Amplifier Gain/Phase
100 TA = 25°C
80
60
40
20
0
–180
–270
–360
10 100 1k 10k 100k 1M 10M
FREQUENCY (Hz)
372212 G07
9.50
0
10 20 30 40 50
ISHUNT (mA)
372212 G02
VREF vs IREF
5.05
5.00 TA = 25°C
TA = 85°C
4.95
4.90
TA = –40°C
4.85
4.80
0
5 10 15 20 25 30 35 40
IREF (mA)
372212 G05
Start-Up ICC vs Temperature
190
180
170
160
150
140
130
120
110
100
–60 –30
0 30 60 90 120 150
TEMPERATURE (°C)
372212 G08
For more information www.linear.com/LTC3722
230
–50 –30 –10 10 30 50 70 90 110 130 150
TEMPERATURE (°C)
372212 G03
VREF vs Temperature
5.01
5.00
4.99
4.98
4.97
4.96
–50 –30 –10 10 30 50 70 90 110 130 150
TEMPERATURE (°C)
372212 G06
Delay Hysteresis Current
vs Temperature
1.302
1.300 SBUS = 1.5V
1.298
1.296
1.294
1.292
1.290
1.288
1.286
1.284
1.282
1.280
–60 –30
0 30 60 90
TEMPERATURE (°C)
120 150
372212 G09
372212fb
5
5 Page 
LTC3722-1/LTC3722-2
OPERATION
3 Internally generated drive signals with programmable
turn-off for current doubler synchronous rectifiers.
Benefit: eliminates external glue logic, drivers, optimal
timing for highest efficiency.
4. Programmable (single resistor) leading edge blanking.
elements are detailed in this data sheet. The secondary
voltage of the transformer is the primary voltage divided
by the transformer turns ratio. Similar to a buck converter,
the secondary square wave is applied to an output filter
inductor and capacitor to produce a well regulated DC
output voltage.
Benefit: prevents spurious operation, reduces external
filtering required on CS.
Switching Transitions
5. Programmable (single resistor) slope compensation.
Benefit: eliminates external glue circuitry.
The phase-shifted full bridge can be described by four
primary operating states. The key to understanding how
ZVS occurs is revealed by examining the states in detail.
6. Optimized current mode control architecture.
Benefit: eliminates glue circuitry, less overshoot at
start-up, faster recovery from system faults.
Each full cycle of the transformer has two distinct periods
in which power is delivered to the output, and two “free-
wheeling” periods. The two sides of the external bridge
have fundamentally different operating characteristics that
7. Programmable system undervoltage lockout and hys-
teresis.
Benefit: provides an accurate turn-on voltage for power
supply and reduces external circuitry.
become important when designing for ZVS over a wide
load current range. The left bridge leg is referred to as the
passive leg, while the right leg is referred to as the active
leg. The following descriptions provide insight as to why
these differences exist.
As a result, the LTC3722-1/LTC3722-2 makes the ZVS topol-
ogy feasible for a wider variety of applications, including State 1 (Power Pulse 1)
those at lower power levels.
As shown in Figure 1, State 1 begins with MA, MD and MF
The LTC3722-1/LTC3722-2 control four external power “ON” and MB, MC and ME “OFF.” During the simultane-
switches in a full bridge arrangement. The load on the
bridge is the primary winding of a power transformer. The
diagonal switches in the bridge connect the primary wind-
ing between the input voltage and ground every oscillator
cycle. The pair of switches that conduct are alternated by
an internal flip-flop in the LTC3722-1/LTC3722-2. Thus,
the voltage applied to the primary is reversed in polarity
on every switching cycle and each output drive signal is
one-half the frequency of the oscillator. The on-time of
ous conduction of MA and MD, the full input voltage is
applied across the transformer primary winding and fol-
lowing the dot convention, VIN/N is applied to the left side
of LO1 allowing current to increase in LO1. The primary
current during this period is approximately equal to the
output inductor current (LO1) divided by the transformer
turns ratio plus the transformer magnetizing current
(VIN • tON)/(LMAG • 2). MD turns off and ME turns on at
the end of State 1.
each driver signal is slightly less than 50%. The on-time
overlap of the diagonal switch pairs is controlled by the
State 2 (Active Transition and Freewheel Interval)
LTC3722-1/LTC3722-2 phase modulation circuitry (refer
to the Block and Timing Diagrams). This overlap sets the
approximate duty cycle of the converter. The LTC3722‑1/
LTC3722-2 driver output signals (OUTA to OUTF) are
optimized for interface with an external gate driver IC or
buffer. External power MOSFETs A and C require high side
driver circuitry, while B and D are ground referenced and E
and F are ground referenced but on the secondary-side of
the isolation barrier. Methods for providing drive to these
MD turns off when the phase modulator comparator transi-
tions. At this instant, the voltage on the MD/MC junction
begins to rise towards the applied input voltage (VIN).
The transformer’s magnetizing current and the reflected
output inductor current propels this action. The slew rate
is limited by MOSFET MC and MD’s outputcapacitance
(COSS), snubbing capacitance and the transformer inter-
winding capacitance. The voltage transition on the active
leg from the ground reference point to VIN will always
372212fb
For more information www.linear.com/LTC3722
11
11 Page | ||
| Páginas | Total 28 Páginas | |
| PDF Descargar | [ Datasheet LTC3722-1.PDF ] | |
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