參數(shù)資料
型號(hào): LTC3766IGN#PBF
廠商: LINEAR TECHNOLOGY CORP
元件分類: 穩(wěn)壓器
英文描述: SWITCHING CONTROLLER, 316 kHz SWITCHING FREQ-MAX, PDSO28
封裝: 0.150 INCH, LEAD FREE, PLASTIC, SSOP-28
文件頁數(shù): 37/60頁
文件大?。?/td> 607K
代理商: LTC3766IGN#PBF
LTC3766
42
3766f
APPLICATIONS INFORMATION
as the communication link between the secondary-side
controller and the primary-side gate driver, as shown in
Figure 28. In addition, LTC3765 contains a bridge recti-
fier that extracts bias power from the pulse transformer,
which it then uses to drive the gates of the primary-side
MOSFETs.
Thedesignshavebeencoordinatedsothatthetransformer
turns ratio should be set to:
NPT = NLTC3765: NLTC3766 = 2:1
for low voltage mode operation on the LTC3766 (VCC =
7V), and:
NPT = NLTC3765: NLTC3766 = 1.5:1
for high voltage mode operation on the LTC3766 (VCC
= 8.5V). The resulting VCC voltage on the LTC3765 is
approximately:
VCC(3765) = VCC(3766)NPT – 1.3
Using the above turns ratios will provide a primary-side
VCC voltage of approximately 12V for the LTC3765 to
drive the gates of the primary-side MOSFET. Note that the
primary-sideVCCvoltageprovidedbythepulsetransformer
must also be greater than the LTC3765 UVLO threshold for
proper operation. Care must also be taken not to exceed
the maximum voltage rating on the LTC3765 VCC pin.
The pulse transformer must also have a minimum volt-
second rating as required by the 79% duty cycle signal
on PT+/PT and the lowest frequency of operation. The
required volt-seconds rating can be calculated from the
minimum frequency as:
Volt-Sec
= 0.33
VCC
fSW(MIN)
Since the pulse transformer is used for transmitting
PWM information as well as bias power, choose a pulse
transformer with a leakage inductance of 1μH or less. This
reduces ringing and distortion of the PWM information
so that a solid communication link is always maintained.
For low voltage (7V) mode on the LTC3766, transformers
thatmeettheaboverequirementsincludethePA2008from
PulseEngineeringandtheDA2320fromCoilcraft.Forhigh
voltage (8.5V) mode on the LTC3766, transformers that
meet the above requirements include the PA3290 from
Pulse Engineering.
The 1F and 0.1F capacitors in series with the pulse
transformer of Figure 28 are for blocking and restoring
the DC level of the signal. The 220pF/100Ω RC snubber
shown at the IN+/INinputs of the LTC3765 is required
to minimize ringing due to the leakage inductance of the
pulse transformer. The values shown for each of these
four components are appropriate in nearly all LTC3765/
LTC3766 applications.
Voltage Loop Compensation
The voltage loop of the LTC3766 is compensated in much
the same way as a standard buck converter, by placing a
compensation network on the ITH pin. It is important to
note, however, that the speed and stability of the voltage
loop is heavily dependent upon several factors apart from
the design of the ITH compensation. Common PCB layout
errors, for example, often appear as stability problems.
Examples include the distant placement of the input de-
coupling capacitor, connecting the ITH compensation to a
ground track carrying significant switch current, and rout-
ing the FB signal over a long distance such that noise pick
occurs. Refer to the PCB Checklist section for additional
information. Another factor that affects the voltage loop
is the choice of output capacitor. If the value is too low, or
the ESR is too high, then it will not be possible to achieve
optimum loop performance. A third factor that can impair
loopresponseisthepresenceofunderdampedresonances
in the power stage. Examples include an underdamped
LC input filter or an active clamp capacitor resonating
with the main transformer magnetizing inductance. Refer
to the Input Capacitor/Filter Selection and Active Clamp
Capacitor sections for details on how to properly damp
these LC resonances. Before attempting to optimize the
loop response, carefully consider the above factors,
IN+
IN
100
0.1F
NLTC3765:NLTC3766
220pF
3766 F28
LTC3765
PT+
PT
LTC3766
1F
Figure 28. Pulse Transformer Connection
相關(guān)PDF資料
PDF描述
LTC3766HGN#TRPBF SWITCHING CONTROLLER, 316 kHz SWITCHING FREQ-MAX, PDSO28
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LTC3766IGN#TRPBF SWITCHING CONTROLLER, 316 kHz SWITCHING FREQ-MAX, PDSO28
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