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参数资料
| 型号： | LTC3835EUFD#PBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 3 A SWITCHING CONTROLLER, 580 kHz SWITCHING FREQ-MAX, PQCC20 |
| 封装： | 4 X 5 MM, LEAD FREE, PLASTIC, MO-220, QFN-20 |
| 文件页数： | 6/30页 |
| 文件大小： | 1775K |
| 代理商： | LTC3835EUFD#PBF |
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LTC3835
14
3835fd
inductancecollapsesabruptlywhenthepeakdesigncurrent
is exceeded. This results in an abrupt increase in inductor
ripple current and consequent output voltage ripple. Do
not allow the core to saturate!
Power MOSFET and Schottky Diode (Optional)
Selection
Two external power MOSFETs must be selected for the
LTC3835: One N-channel MOSFET for the top (main)
switch, and one N-channel MOSFET for the bottom (syn-
chronous) switch.
Thepeak-to-peakdrivelevelsaresetbytheINTVCCvoltage.
Thisvoltageistypically5Vduringstart-up(seeEXTVCCPin
Connection).Consequently,logic-levelthresholdMOSFETs
must be used in most applications. The only exception
is if low input voltage is expected (VIN < 5V); then, sub-
logic level threshold MOSFETs (VGS(TH) < 3V) should be
used. Pay close attention to the BVDSS specification for
the MOSFETs as well; most of the logic level MOSFETs are
limited to 30V or less.
Selection criteria for the power MOSFETs include the “ON”
resistance RDS(ON), Miller capacitance CMILLER, input
voltage and maximum output current. Miller capacitance,
CMILLER, can be approximated from the gate charge curve
usually provided on the MOSFET manufacturers’ data
sheet. CMILLER is equal to the increase in gate charge
along the horizontal axis while the curve is approximately
flat divided by the specified change in VDS. This result is
then multiplied by the ratio of the application applied VDS
to the Gate charge curve specified VDS. When the IC is
operating in continuous mode the duty cycles for the top
and bottom MOSFETs are given by:
Main Switch Duty Cycle
=
VOUT
VIN
Synchronous Switch Duty Cycle
=
VIN – VOUT
VIN
The MOSFET power dissipations at maximum output
current are given by:
PMAIN =
VOUT
VIN
IMAX
( )2 1+d
( )RDS(ON) +
VIN
( )2 IMAX
2
RDR
( ) CMILLER
(
)
1
VINTVCC – VTHMIN
+
1
VTHMIN
f
( )
PSYNC =
VIN – VOUT
VIN
IMAX
( )2 1+d
( )RDS(ON)
where
d is the temperature dependency of RDS(ON) and
RDR (approximately 2Ω) is the effective driver resistance
at the MOSFET’s Miller threshold voltage. VTHMIN is the
typical MOSFET minimum threshold voltage.
BothMOSFETshaveI2RlosseswhilethetopsideN-channel
equation includes an additional term for transition losses,
which are highest at high input voltages. For VIN < 20V
the high current efficiency generally improves with larger
MOSFETs, while for VIN > 20V the transition losses rapidly
increase to the point that the use of a higher RDS(ON)device
with lower CMILLERactuallyprovideshigherefficiency.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+
d) is generally given for a MOSFET in the
form of a normalized RDS(ON) vs Temperature curve, but
d = 0.005/°C can be used as an approximation for low
voltage MOSFETs.
TheoptionalSchottkydiodeD1showninFigure6conducts
during the dead-time between the conduction of the two
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 that
could cost as much as 3% in efficiency at high VIN. A 1A
to 3A Schottky is generally a good compromise for both
regions of operation due to the relatively small average
current.Largerdiodesresultinadditionaltransitionlosses
due to their larger junction capacitance.
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| LTC3835IDHC-1#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 16-DFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:4,500 系列:PowerWise® PWM 型:控制器 输出数:1 频率 - 最大:1MHz 占空比:95% 电源电压:2.8 V ~ 5.5 V 降压:是 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:6-WDFN 裸露焊盘 包装:带卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名称:LM1771SSDX |
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| LTC3835IFEPBF | 制造商:Linear Technology 功能描述:DC-DC Controller Step-Down 4-36V TSSOP20 |
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