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参数资料
| 型号： | LTC3728IG |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 3 A DUAL SWITCHING CONTROLLER, 590 kHz SWITCHING FREQ-MAX, PDSO28 |
| 封装： | 0.209 INCH, PLASTIC, SSOP-28 |
| 文件页数： | 8/36页 |
| 文件大小： | 1661K |
| 代理商： | LTC3728IG |
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LTC3728
16
3728fg
load transient response and sufcient ripple current sig-
nal in the current loop. The maximum ΔIL occurs at the
maximum input voltage.
The inductor value also has secondary effects. The tran-
sition to Burst Mode operation begins when the average
inductor current required results in a peak current below
25% of the current limit determined by RSENSE. Lower
inductor values (higher ΔIL) will cause this to occur at
lower load currents, which can cause a dip in efciency in
the upper range of low current operation. In Burst Mode
operation, lower inductance values will cause the burst
frequency to decrease.
Inductor Core Selection
Once the value for L is known, the type of inductor must
be selected. High efciency converters generally cannot
afford the core loss found in low cost powdered iron cores,
forcing the use of more expensive ferrite, molypermalloy,
or Kool Mμ cores. Actual core loss is independent of core
size for a xed inductor value, but it is very dependent
on inductance selected. As inductance increases, core
losses go down. Unfortunately, increased inductance
requires more turns of wire and therefore copper losses
will increase.
Ferrite designs have very low core loss and are preferred
at high switching frequencies, so design goals can con-
centrate on copper loss and preventing saturation. Ferrite
core material saturates hard, which means that induc-
tance collapses abruptly when the peak design current is
exceeded. This results in an abrupt increase in inductor
ripple current and consequent output voltage ripple. Do
not allow the core to saturate!
Molypermalloy (from Magnetics, Inc.) is a very good, low
loss core material for toroids, but it is more expensive
than ferrite. A reasonable compromise from the same
manufacturer is Kool Mμ. Toroids are very space efcient,
especially when you can use several layers of wire. Because
they generally lack a bobbin, mounting is more difcult.
However, designs for surface mount are available that do
not increase the height signicantly.
APPLICATIONS INFORMATION
Power MOSFET and D1 Selection
Two external power MOSFETs must be selected for each
controller in the LTC3728: One N-channel MOSFET for
the top (main) switch, and one N-channel MOSFET for
the bottom (synchronous) switch.
The peak-to-peak drive levels are set by the INTVCC
voltage. This voltage is typically 5V during start-up
(see EXTVCC Pin Connection). Consequently, logic-level
threshold MOSFETs must be used in most applications.
The only exception is if low input voltage is expected
(VIN<5V);then,sublogiclevelthresholdMOSFETs(VGS(TH)
< 3V) should be used. Pay close attention to the BVDSS
specication 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), reverse-transfer capacitance CRSS,
input voltage and maximum output current. When the
LTC3728 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+
()R
DS(ON) +
kVIN
()2 I
MAX
() C
RSS
() f()
PSYNC =
VIN –VOUT
VIN
IMAX
()2 1+
()R
DS(ON)
where
δ is the temperature dependency of RDS(ON) and k
is a constant inversely related to the gate drive current.
Both MOSFETs have I2R losses while the topside N-channel
equation includes an additional term for transition losses,
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| LTC3728IG#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 28-SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:PolyPhase® 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 |
| LTC3728IG#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 28-SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:PolyPhase® 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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