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(yè)數(shù)： 15/60頁(yè)
文件大?。?/td> 607K
代理商： LTC3766IGN#PBF
LTC3766
22
3766f
APPLICATIONS INFORMATION
Be careful to keep these divider resistors very close to the
FB pin to minimize the trace length and noise pick-up on
the sensitive FB signal. Using a low resistance (<2k) for
the output voltage divider also minimizes noise on the FB
pin. If the remote sense amplifier is used, then the divider
should be placed between the VSOUT pin and GND. See
the Remote Sensing section for details.
of power level, choose a family of transformers whose
rated power level exceeds that of the required amount of
output power. Be careful to allow for room to “grow,” as
the power requirements of many electronic systems tend
to increase throughout development.
Once a family of transformers has been selected, the
next step is to choose a suitable transformer from within
that family. This mainly consists of choosing the correct
number of primary and secondary turns (NP and NS). The
value of NS can be calculated from:
NS =
108 VOUT
fSWACBM
where AC is the cross-sectional area of the core in cm2 (as
normally given in the transformer data sheet) and BMisthe
maximum AC flux density desired. For the Pulse PA08xx
seriespowertransformersusedintheTypicalApplications
section, AC = 0.59cm2. For the Pulse PA09xx series power
transformers, AC = 0.81cm2. Most high frequency trans-
formersuseaferritecorematerial.Consequently,selecting
a maximum AC flux density of 2000 gauss is normally a
good starting point, provided that the switching frequency
is between 150kHz and 350kHz. This value of BM leaves
headroom during transients and avoids excessive core
losses. Note that the choice of BM together with switch-
ing frequency will determine the amount of core loss for
a given transformer. Consult the transformer data sheet to
evaluate the resulting core loss and temperature rise. In
some cases, it may be necessary to increase NSsomewhat
in order to reduce BM and the associated temperature rise.
In all cases, be sure to stay well below the saturation flux
density of the transformer core.
Once the value of has NS been selected, the required
transformer turns ratio can be calculated from
NP
NS
=
DMAXVIN(MIN)
VOUT
where VIN(MIN) is the minimum input voltage and DMAX
is the maximum duty cycle. Although the LTC3766 has a
maximum duty cycle of 79% (DMAX = 0.79), normally a
lower value of DMAX is chosen in the above equation so
that there is duty cycle headroom to accommodate load
Figure 7. Setting the Output Voltage
VFB
RB
RA
LTC3766
VOUT
3766 F07
Selecting the Main Transformer
The job of the transformer in a forward converter is to
step the voltage either up or down while providing isola-
tion between the primary and secondary grounds. Ideally,
this transformer would not store any energy (it would have
infinite magnetizing inductance). Note that this objective
is very different from that of the transformer used in a
flyback converter. The transformer used in a flyback con-
verter is really a coupled inductor, the purpose of which is
to store energy during the primary-side on time and then
deliver it to the secondary during the off-time. In a forward
converter, by contrast, the power is transferred during the
primary-side on-time, and the off-time is used to recover
the small amount of energy that was inadvertently stored
in the core of the transformer.
Fornearlyallapplications,anoff-the-shelftransformercan
beselected.Transformersusingplanarwindingtechnology
are widely available and are a good choice for minimizing
leakage inductance as well as component height. There
are two basic items to consider in selecting an appropri-
ate family of off-the-shelf transformers: 1) the isolation
requirements and 2) the power level requirements. If the
application circuit has specific isolation requirements,
choose a family of transformers whose isolation level
satisfies that requirement. In addition to an isolation volt-
age rating, the application may require a transformer with
certification from a particular agency, or it may require a
specifictypeofisolation(e.g.,basicorfunctional).Interms
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LTC3766IUFD#TRPBF 功能描述:IC CONTROLLER SYNCH 28QFN RoHS:是 類別:集成電路 (IC) >> PMIC - 電源控制器，監(jiān)視器 系列:Direct Flux Limit™, PolyPhase® 產(chǎn)品培訓(xùn)模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標(biāo)準(zhǔn)包裝:2,500 系列:- 應(yīng)用:多相控制器 輸入電壓:- 電源電壓:9 V ~ 14 V 電流 - 電源:- 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:40-WFQFN 裸露焊盤 供應(yīng)商設(shè)備封裝:40-TQFN-EP（5x5） 包裝:帶卷 (TR)
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LTC3766MPGN#TRPBF 功能描述:IC CONTROLLER SYNCH 28SSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 電源控制器，監(jiān)視器 系列:Direct Flux Limit™, PolyPhase® 產(chǎn)品培訓(xùn)模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標(biāo)準(zhǔn)包裝:2,500 系列:- 應(yīng)用:多相控制器 輸入電壓:- 電源電壓:9 V ~ 14 V 電流 - 電源:- 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:40-WFQFN 裸露焊盤 供應(yīng)商設(shè)備封裝:40-TQFN-EP（5x5） 包裝:帶卷 (TR)
LTC3766MPUFD#PBF 功能描述:IC CONTROLLER SYNCH 28QFN RoHS:是 類別:集成電路 (IC) >> PMIC - 電源控制器，監(jiān)視器 系列:Direct Flux Limit™, PolyPhase® 產(chǎn)品培訓(xùn)模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標(biāo)準(zhǔn)包裝:2,500 系列:- 應(yīng)用:多相控制器 輸入電壓:- 電源電壓:9 V ~ 14 V 電流 - 電源:- 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:40-WFQFN 裸露焊盤 供應(yīng)商設(shè)備封裝:40-TQFN-EP（5x5） 包裝:帶卷 (TR)
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