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參數資料
| 型號： | LT3782IFE#TR |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 4 A SWITCHING CONTROLLER, 533 kHz SWITCHING FREQ-MAX, PDSO28 |
| 封裝： | 4.40 MM, PLASTIC, TSSOP-28 |
| 文件頁數： | 19/20頁 |
| 文件大?。?/td> | 223K |
| 代理商： | LT3782IFE#TR |
LT3782
8
3782fg
Operation
The LT3782 is a two phase constant frequency current mode
boost controller. Switching frequency can be programmed
up to 500kHz. During normal switching cycles, the two
channels are controlled by internal ip-ops and are 180
degrees out-of-phase.
Referring to the Block Diagram, the LT3782’s basic func-
tions include a transconductance amplifer (gm) to regulate
the output voltage and to control the current mode PWM
current loop. It also includes the necessary logic and ip-
op to control the PWM switching cycles, two high speed
gate drivers to drive high power N-Channel MOSFETs, and
2-phase control signals to drive external gate drivers for
optional synchronous operation.
In normal operation, each switching cycle starts with a
switch turn-on. The inductor current of each channel is
sampled through the current sense resistor and amplied
then compared to the error amplier output VC to turn
the switch off. The phase delay of the second channel is
controlled by the divide-by-two D ip-op and is exactly
180 degrees out-of-phase of the rst channel. With a re-
sistor divider connected to the FB pin, the output voltage
is programmed to the desired value. The 10V gate drivers
are sufcient to drive most high power N-channel MOSFET
in many industrial applications.
Additional important features include shutdown, cur-
rent limit, soft-start, synchronization and programmable
maximum duty cycle. Additional slope compensation can
be added also.
Output Voltage Programming
With a 2.44V feedback reference voltage VREF, the output
VOUT is programmed by a resistor divider as shown in
the Block Diagram.
VOUT = 2.44 1+
RF1
RF2
Soft-Start and Shutdown
During soft-start, the voltage on the SS pin (VSS) controls
the output voltage. The output voltage thus ramps up fol-
lowing VSS. The effective range of VSS is from 0V to 2.44V.
The typical time for the output to reach the programmed
level is
t
=
C 2.44V
10
μA
C is the capacitor connected from the SS pin to Gnd.
Undervoltage Lockout and Shutdown
Only when VRUN is higher than 2.45V VGBIAS will be ac-
tive and the switching enabled. The LT3782 goes into low
current shutdown when VRUN is below 0.3V. A resistor
divider can be used on RUN pin to set the desired VCC
undervoltage lockout voltage. 80mV of hysteresis is built
in on RUN pin thresholds.
Oscillation Frequency Setting and Synchronization
The switching frequency of LT3782 can be set up to 500kHz
by a resistor RFREQ from pin RSET to ground.
For fSET = 250kHz, RFREQ = 80k
Once the switching frequency fSET is chosen, RFREQ can be
found from the Switching Frequency vs RFREQ graph found
under the Typical Performance Characteristics section.
Note that because of the 2-phase operation, the internal
oscillator is running at twice the switching frequency. To
synchronize the LT3782 to the system frequency fSYSTEM,
the synchronizing frequency fSYNC should be two times
fSYSTEM, and the LT3782 switching frequency fSET should
be set below 80% of fSYSTEM.
fSYNC = 2fSYSTEM and fSET < (fSYSTEM 0.8)
For example, to synchronize the LT3782 to 200kHz system
frequency fSYSTEM,fSYNCneedstobesetat400kHzandfSET
needs to be set at 160kHz. From the Switching Frequency
vs RFREQ graph found under the Typical Performance
Characteristics section, RFREQ = 130k.
APPLICATIONS INFORMATION
相關PDF資料 |
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| LT3782IFE | 4 A SWITCHING CONTROLLER, 533 kHz SWITCHING FREQ-MAX, PDSO28 |
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| LT3845AMPFE#TRPBF | SWITCHING CONTROLLER, 500 kHz SWITCHING FREQ-MAX, PDSO16 |
| LT3845AIFE#TRPBF | SWITCHING CONTROLLER, 500 kHz SWITCHING FREQ-MAX, PDSO16 |
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