參數(shù)資料
型號(hào)： LTC3775EMSE#TRPBF
廠商： LINEAR TECHNOLOGY CORP
元件分類： 穩(wěn)壓器
英文描述： SWITCHING CONTROLLER, 575 kHz SWITCHING FREQ-MAX, PDSO16
封裝： LEAD FREE, PLASTIC, MSOP-16
文件頁數(shù)： 14/34頁
文件大?。?/td> 534K
代理商： LTC3775EMSE#TRPBF
LTC3775
21
3775fa
CMILLER = Calculated Miller capacitance using the gate
charge curve from the MOSFET data sheet
fSW = Switching frequency
Both MOSFETs have conduction losses (I2R) while the
topside N-channel equation includes an additional term
for transition losses, which peak at the highest input volt-
age. For VIN < 12V, the high current efciency generally
improves with larger MOSFETs, while for VIN > 12V, the
transition losses rapidly increase to the point that the use
of a higher RDS(ON) device with lower CMILLER actually
provides higher efciency. The bottom MOSFET losses are
greatest at high input voltage when the top switch duty
factor is low or during a short circuit when the bottom
switch is on close to 100% of the period.
Schottky Diode Selection
An optional Schottky diode connected between the SW node
(cathode) and the source of the bottom MOSFET (anode)
conducts during the dead time between the conduction of
the power MOSFET switches. It is intended to prevent the
body diode of the bottom MOSFET from turning on and
storing a charge during the dead time, which can cause
a modest (about 1%) efciency loss. The diode can be
rated for about one half to one fth of the full load current
since it is on for only a fraction of the duty cycle. In order
for the diode to be effective, the inductance between it
and the bottom MOSFET must be as small as possible,
mandating that these components be placed next to each
other on the same layer of the PC board.
Input Capacitor Selection
The input bypass capacitor has three primary requirements:
its ESR must be low to minimize the supply drop when
the top MOSFETs turn on, its RMS current capability must
be adequate to withstand the ripple current at the input,
and its capacitance must be large enough to maintain the
input voltage until the input supply can respond. Generally,
a capacitor (particularly a non-ceramic type) that meets
the rst two parameters will have far more capacitance
than is required to keep capacitance-based droop under
control. The input capacitor’s voltage rating should be at
least 1.4 times the maximum input voltage.
In continuous mode, the source current of the top N-channel
MOSFET is approximately a square wave of duty cycle VOUT/
VIN. The maximum RMS capacitor current is given by:
II
VV
V
RMS
OUT MAX
OUT
IN
OUT
IN
≈
()
–
This formula has a maximum at VIN = 2VOUT, where
IRMS = IOUT/2. This simple worst-case condition is com-
monly used for design because even signicant deviations
do not offer much relief.
Note that capacitor manufacturer’s ripple current ratings
are often based on only 2000 hours of life. This makes
it advisable to further derate the capacitor or to choose
a capacitor rated at a higher temperature than required.
Several capacitors may also be paralleled to meet size or
height requirements in the design. Always consult the
manufacturer if there is any question.
Medium voltage (20V to 35V) ceramic, tantalum, OS-CON
and switcher-rated electrolytic capacitors can be used
as input capacitors, but each has drawbacks: ceramics
have high voltage coefcients of capacitance and may
have audible piezoelectric effects; tantalums need to be
surge-rated; OS-CONs suffer from higher inductance,
larger case size and limited surface mount applicability;
and electrolytics’ higher ESR and dryout may require
several to be used in parallel. Sanyo OS-CON SVP, SVPD
series; Sanyo POSCAP TQC series or aluminum electrolytic
capacitors from Panasonic WA series or Cornel Dublilier
SPV series, in parallel with a couple of high performance
ceramic capacitors, can be used as an effective means of
achieving low ESR and high bulk capacitance.
Output Capacitor Selection
The selection of COUT is primarily determined by the ESR
required to minimize voltage ripple and load step transients.
The output ripple ΔVOUT is approximately bounded by:
VOUT
IL ESR+
1
8 fSW COUT
where ΔIL is the inductor ripple current.
APPLICATIONS INFORMATION
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
LTC3775EUD#PBF 功能描述:IC REG CTRLR BUCK PWM VM 16-QFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)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)
LTC3775EUD#PBF 制造商:Linear Technology 功能描述:IC SYNC STEP-DOWN DC/DC CONTROLLER QFN16
LTC3775EUD#TRPBF 功能描述:IC REG CTRLR BUCK PWM VM 16-QFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)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)
LTC3775IMSE#PBF 功能描述:IC REG CTRLR BUCK PWM VM 16-MSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)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)
LTC3775IMSE#TRPBF 功能描述:IC REG CTRLR BUCK PWM VM 16-MSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)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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