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PDF LTC1922-1 Data sheet ( Hoja de datos )
| Número de pieza | LTC1922-1 | |
| Descripción | Synchronous Phase ModEGZ12DCFulated Full-Bridge Controller | |
| Fabricantes | Linear | |
| Logotipo |  |
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LTC1922-1
Synchronous Phase
Modulated Full-Bridge Controller
FEATURES
DESCRIPTIO
s Adaptive DirectSenseTM Zero Voltage Switching
s Integrated Synchronous Rectification Control for
Highest Efficiency
s Output Power Levels from 50W to Kilowatts
s Very Low Start-Up and Quiescent Currents
s Compatible with Voltage Mode and Current Mode
Topologies
s Programmable Slope Compensation
s Undervoltage Lockout Circuitry with 4.2V Hysteresis
and Integrated 10.3V Shunt Regulator
s Fixed Frequency Operation to 1MHz
s 50mA Outputs for Bridge Drive and Secondary Side
Synchronous Rectifiers
s Soft-Start, Cycle-by-Cycle Current Limiting and
Hiccup Mode Short-Circuit Protection
s 5V, 15mA Low Dropout Regulator
s 20-Pin PDIP and SSOP Packages
U
APPLICATIO S
s Telecommunications, Infrastructure Power Systems
s Distributed Power Architectures
s Server Power Supplies
s High Density Power Modules
The LTC®1922-1 phase shift PWM controller provides all
of the control and protection functions necessary to imple-
ment a high performance, zero voltage switched, phase
shift, full-bridge power converter with synchronous recti-
fication. The part is ideal for developing isolated, low
voltage, high current outputs from a high voltage input
source. The LTC1922-1 combines the benefits of the full-
bridge topology with fixed frequency, zero voltage switch-
ing operation (ZVS). Adaptive ZVS circuity controls the
turn-on signals for each MOSFET independent of internal
and external component tolerances for optimal perfor-
mance.
The LTC1922-1 also provides secondary side synchro-
nous rectifier control. The device uses peak current mode
control with programmable slope comp and leading edge
blanking.
The LTC1922-1 features extremely low operating and
start-up currents to simplify off-line start-up and bias
circuitry. The LTC1922-1 also includes a full range of
protection features and is available in 20-pin through hole
(N) and surface mount (G) packages.
, LTC and LT are registered trademarks of Linear Technology Corporation.
DirectSense is a trademark of Linear Technology Corporation.
TYPICAL APPLICATIO
BIAS
SUPPLY
VIN
48V
LTC1922-1
VOUT
3.3V
ISOLATED
FEEDBACK
Efficiency
100
90
VIN = 48V
80
VIN = 36V
70
60
0
10 20 30
LOAD CURRENT (A)
40
1922 • TA01b
1922 TA01a
1
1 page  
TYPICAL PERFOR A CE CHARACTERISTICS
LTC1922-1
Start-Up ICC vs Temperature
160
150
140
130
120
110
100
90
80
70
–55
–25 5 35 65
TEMPERATURE (°C)
95 125
1922 • G10
Delay Hysteresis Current vs
Temperature
1.278
SBUS = 1.5V
1.276
1.274
1.272
1.270
1.268
1.266
1.264
1.262
1.260
1.258
1.256
–55 –25
5
35 65 95 125
TEMPERATURE (°C)
1922 • G11
Slope Current vs Temperature
130
120 CT = 3.0V
110
100
90
80
70
60 CT = 1.5V
50
40
–55 –25
5
35 65 95 125
TEMPERATURE (°C)
1922 • G12
VCC Shunt Voltage vs Temperature
10.5
ICC = 10mA
10.4
10.3
10.2
10.1
10.0
9.9
9.8
–55
–25 5 35 65
TEMPERATURE (°C)
95 125
1922 • G13
Delay Pin Threshold vs
Temperature
2.4
2.3 SBUS = 2.25V
2.2
2.1
2.0
1.9
1.8
1.7
1.6
SBUS = 1.5V
1.5
1.4
–55
–25 5 35 65
TEMPERATURE (°C)
95 125
1922 • G14
FB Input Voltage vs Temperature
1.202
1.201
1.200
1.199
1.198
1.197
1.196
1.195
1.194
–55
–25 5 35 65
TEMPERATURE (°C)
95 125
1922 • G15
Ramp Offset Voltage vs
Temperature
390
385
380
375
370
365
360
355
350
–55
–25 5 35 65
TEMPERATURE (°C)
95 125
1922 • G16
5
5 Page 
U
OPERATIO
Zero Voltage Switching (ZVS)
A lossless switching transition requires that the respective
full-bridge MOSFETs be switched to the “ON” state at the
exact instant their drain to source voltage is zero. Delaying
the turn-on results in lower efficiency due to circulating
current flowing in the body diode of the primary side
MOSFET rather than its low resistance channel. Premature
turn-on produces hard switching of the MOSFETs, in-
creasing noise and power dissipation. Previous solutions
have attempted to meet these requirements with fixed or
first order (linear) variable open-loop time delays. Open-
loop methods typically set the turn-on delay to the worst
case longest bridge transition time expected plus the
tolerances of all the internal and external delay timing
circuitry. These error tolerances can be quite significant,
while the optimal transition times over the load current
range vary nonlinearly. In a volume production environ-
ment, these factors can necessitate an external trim to
guarantee ZVS operation, adding cost to the final product.
An additional side effect of longer than required delays is
a decrease in the effective maximum duty cycle. Reduced
duty cycle range can mandate a lower transformer turns
ratio, impacting efficiency or requiring a lower switching
frequency, impacting size.
LTC1922-1 Adaptive Delay Circuitry
The LTC1922-1 addresses the issue of nonideal switching
delays with novel DirectSense circuitry that intelligently
monitors both the input supply and instantaneous bridge
leg voltages, and commands a switching transition when
the expected zero voltage condition is reached. In effect,
the LTC1922-1 “closes the loop” on the ZVS turn-on delay
requirements. DirectSense technology provides optimal
turn-on delay timing, regardless of input voltage, output
load, or component tolerances and greatly simplifies the
power supply design process. The DirectSense technique
requires only a simple voltage divider sense network to
implement. If there is not enough energy to fully commu-
tate the bridge leg to a ZVS condition, the LTC1922-1
automatically overrides the DirectSense circuitry and forces
a transition. The LTC1922-1 delay circuitry can also be
overridden, by tying SBUS to VREF.
LTC1922-1
Adaptive Mode
The LTC1922-1 is configured for adaptive delay sensing
with three pins, ADLY, PDLY and SBUS. ADLY and PDLY
sense the active and passive delay legs respectively via a
voltage divider network as shown in Figure 2.
VIN
SBUS
PDLY
R2 A
R5
R1
R3
1k
B
C
D
RCS
ADLY
R6
R4
1k
1922 F02
Figure 2. Adaptive Mode
The threshold voltage on PDLY and ADLY for both the
rising and falling transitions is set by the voltage on SBUS.
A buffered version of this voltage is used as the threshold
level for the internal DirectSense circuitry. At nominal VIN,
the voltage on SBUS is set to 1.5V by an external voltage
divider between VIN and GND, making this voltage directly
proportional to VIN. The LTC1922-1 DirectSense circuitry
uses this characteristic to zero voltage switch all of the
external power MOSFETs, independent of input voltage.
ADLY and PDLY are connected through voltage dividers to
the active and passive bridge legs respectively. The lower
resistor in the divider is set to 1k. The upper resistor in the
divider is divided into one, two or three equal value
resistors to reduce its overall capacitance. In off-line
applications, this is usually required anyway to stay within
the maximum voltage ratings of the resistors. One or two
resistor segments will work for most nominal 48V or lower
VIN applications.
To set up the ADLY and PDLY resistors, first determine at
what drain to source voltage to turn-on the MOSFETs.
Finite delays exist between the time at which the LTC1922-1
controller output transitions, to the time at which the
power MOSFET switches on due to MOSFET turn on delay
and external driver circuit delay. Ideally, we want the
power MOSFET to switch at the instant there is zero volts
across it. By setting a threshold voltage for ADLY and
11
11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet LTC1922-1.PDF ] | |
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