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參數(shù)資料
| 型號： | LTC3766MPUFD#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, PQCC28 |
| 封裝： | 4 X 5 MM, LEAD FREE, PLASTIC, MO-220, QFN-28 |
| 文件頁數(shù)： | 9/60頁 |
| 文件大?。?/td> | 607K |
| 代理商： | LTC3766MPUFD#PBF |
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LTC3766
17
3766f
OPERATION
directly measured and limited through a sense resistor
in series with the PMOS source. This prevents saturation
in the negative direction. When the PMOS turns off and
the main NMOS switch turns on, the LTC3765 generates
an accurate internal estimate of the magnetizing current
based on the sensed input voltage on the LTC3765 RUN
pin and transformer core parameters customized to the
particular core by a resistor from the LTC3765 RCORE pin
to ground. The magnetizing current is then limited during
theon-timebythisaccurateinternalapproximation.Unlike
previous methods, the direct flux limit directly measures
and monitors flux accumulation and guarantees that the
transformer will not saturate in either direction, even
when starting into a pre-biased output. This technique
also provides the best possible transient response, as it
will temporarily allow very high duty cycles, only limiting
the duty cycle when absolutely necessary. Moreover, this
techniquepreventsovercurrentdamagetotheactiveclamp
PMOS, which is a potentially significant weakness in many
active clamp forward converter designs.
Additional Protection Features
The LTC3766 contains a wide array of protection features,
which protect the DC/DC converter in the event that ab-
normalconditionspersist.Ingeneral,protectionsfeatures
are either classified as a fault or a limit. When a fault is
detected, all switching stops and the LTC3766 initiates a
soft-start retry. Faults of this nature include overcurrent,
overtemperature, differential amplifier miswire and
communication-lock fault.
An overcurrent fault occurs if the peak current exceeds
approximately 133% of its normal value during current
limit. Note that when inductor ripple cancellation is used,
the value of the peak current during current limit will vary
with inductor current ripple. The overtemperature fault is
set at 165°C, with 20°C of hysteresis. This is helpful for
limiting the temperature of the DC/DC converter in the
event of some external device failure or other abnormal
condition. The differential amplifier wiring fault is gener-
ated if the inputs on the differential amplifier are reversed,
or if there is not enough voltage on the VIN pin to support
the voltage needed on VSOUT. This is important to avoid
an overvoltage condition on the output. Finally, since it is
essential that the LTC3766 be in constant communication
with the LTC3765, a loss of communication lock will also
generate a fault. A lock condition is detected by monitoring
the SW node voltage, and ensuring that it is both rising
and falling as it should in response to the PWM signal
being sent to the primary side. If the SW node voltage
is not rising and falling in an appropriate manner, than a
lock fault is generated.
In addition to the four protection features that generate
faults,therearealsofourprotectionfeaturesthatestablisha
clamporlimit,withoutgeneratingafault.First,theLTC3766
contains a precision volt-second clamp. This feature is not
needed when the LTC3766 is used in conjunction with the
LTC3765,whichincorporatesthedirectfluxlimitfeature.If
the LTC3766 is used standalone, however, the volt-second
limit can be used by placing a resistor from the SW node to
the VSEC pin and a capacitor from VSEC to GND. When the
SW node is low, the capacitor is discharged by an on-chip
NMOS. When the SW node is high, the capacitor on VSEC
is charged. If the capacitor voltage exceeds an internally
generated threshold, then the main primary switch will be
turnedoff,therebylimitingthevolt-secondproductapplied
tothemaintransformer.Tocompensatefortheexponential
nature of the RC charging circuit, the LTC3766 adjusts the
threshold of the volt-second comparator according to:
VSEC(TH) = 0.6–
0.16
VSW(HI)
where VSW(HI) is the voltage on the SW pin during the
on-time of the primary switch. This keeps the volt-second
limit essentially constant for SW node voltages in the
range of 2V to 40V.
Second,intheeventthatthemainoutputvoltageexceedsits
regulationtargetbymorethan17%,theLTC3766willdetect
an overvoltage condition. If this happens, the LTC3766
will immediately turn off the main primary MOSFET and
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| LTC3770EG#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 28-SSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標準包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無 升壓:是 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR) |
| LTC3770EG#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 28-SSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標準包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無 升壓:是 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR) |
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