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參數(shù)資料
| 型號： | LTC3773EUHF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | SWITCHING CONTROLLER, 700 kHz SWITCHING FREQ-MAX, PQCC38 |
| 封裝： | 5 X 7 MM, PLASTIC, MO-220WHKD, QFN-38 |
| 文件頁數(shù)： | 9/32頁 |
| 文件大?。?/td> | 461K |
| 代理商： | LTC3773EUHF |
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LTC3773
17
3773fa
where
δ is the temperature dependency of RDS(ON), RDR
is the effective top driver resistance (approximately 2
Ω
at VGS = VMILLER), and VIN is the drain potential and the
change in drain potential in the particular application.
VTH(IL) is the typical gate threshold voltage shown in the
power MOSFET data sheet at the specied drain current.
CMILLER is the calculated capacitance using the gate charge
curve from the MOSFET data sheet and the technique
described above.
Both MOSFETs have I2R losses while the topside N-channel
equation includes an additional term for transition losses,
which peak at the highest input voltage. 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
synchronous MOSFET losses are greatest at high input
voltage when the top switch duty factor is low or during
a short-circuit when the synchronous switch is on close
to 100% of the period.
The term (1 +
δ) is generally given for a MOSFET in the
form of a normalized RDS(ON) vs temperature curve, but
δ = 0.005/°C can be used as an approximation for low
voltage MOSFETs.
The Schottky diodes in Figure 1 conduct during the dead
time between the conduction of the two large power
MOSFETs. This prevents the body diode of the bottom
MOSFET from turning on, storing charge during the dead
time and requiring a reverse recovery period which could
cost as much as several percent in efciency. A 2A to 8A
Schottky is generally a good compromise for both regions
of operation due to the relatively small average current.
Larger diodes result in additional transition loss due to
their larger junction capacitance.
CIN and COUT Selection
The selection of CIN is simplied by the 3-phase architec-
ture and its impact on the worst-case RMS current drawn
through the input network (battery/fuse/capacitor). It can
be shown that the worst-case capacitor RMS current oc-
curs when only one controller is operating. The controller
with the highest (VOUT)(IOUT) product needs to be used to
determine the maximum RMS capacitor current require-
ment. Increasing the output current drawn from the other
controller will actually decrease the input RMS ripple cur-
rent from its maximum value. The out-of-phase technique
typically reduces the input capacitor’s RMS ripple current
by a factor of 30% to 70% when compared to a single
phase power supply solution.
The type of input capacitor, value and ESR rating have ef-
ciency effects that need to be considered in the selection
process. The capacitance value chosen should be sufcient
to store adequate charge to keep high peak battery currents
down. The ESR of the capacitor is important for capacitor
power dissipation as well as overall battery efciency. All
the power (RMS ripple current ESR) not only heats up
the capacitor but wastes power from the battery.
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 dry out possibility require
several to be used. Sanyo OS-CON SVP, SVPD series; Sanyo
POSCAP TQC series or aluminum electrolytic capacitors
from Panasonic WA series or Cornell Dubilier SPV series,
in parallel with a couple of high performance ceramic ca-
pacitors, can be used as an effective means of achieving
low ESR and large bulk capacitance. Multiphase systems
allow the lowest amount of capacitance overall. As little
as one 22F or two to three 10F ceramic capacitors are
an ideal choice in 20W to 35W power supplies due to their
extremely low ESR. Even though the capacitance at 20V
is substantially below their rating at zero-bias, very low
ESR loss makes ceramics an ideal candidate for highest
efciency battery operated systems.
In continuous mode, the source current of the top N-chan-
nel MOSFET is a square wave of duty cycle VOUT/VIN. To
prevent large voltage transients, a low ESR input capaci-
tor sized for the maximum RMS current of one channel
must be used. The maximum RMS capacitor current is
given by:
II
VV
V
RMS
OUT MAX
OUT
IN
OUT
IN
≈
()
(–
)
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| LTC3773EUHF#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 38-QFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:PolyPhase® 標準包裝:4,500 系列:PowerWise® PWM 型:控制器 輸出數(shù):1 頻率 - 最大:1MHz 占空比:95% 電源電壓:2.8 V ~ 5.5 V 降壓:是 升壓:無 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:6-WDFN 裸露焊盤 包裝:帶卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名稱:LM1771SSDX |
| LTC3774EUHE#PBF | 制造商:Linear Technology 功能描述:SWITCHING REG, BUCK, ADJ, 2.2MHZ, DFN-36 |
| LTC3774IUHE#PBF | 制造商:Linear Technology 功能描述:SWITCHING REG, BUCK, ADJ, 2.2MHZ, DFN-36 |
| LTC3775EMSE#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:- 特色產(chǎn)品:LM3753/54 Scalable 2-Phase Synchronous Buck Controllers 標準包裝:1 系列:PowerWise® PWM 型:電壓模式 輸出數(shù):1 頻率 - 最大:1MHz 占空比:81% 電源電壓:4.5 V ~ 18 V 降壓:是 升壓:無 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-5°C ~ 125°C 封裝/外殼:32-WFQFN 裸露焊盤 包裝:Digi-Reel® 產(chǎn)品目錄頁面:1303 (CN2011-ZH PDF) 其它名稱:LM3754SQDKR |
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