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参数资料
| 型号： | LTC3772EDDB#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 11/20页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 8-DFN |
| 标准包装： | 2,500 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 650kHz |
| 占空比： | 100% |
| 电源电压： | 2.75 V ~ 9.8 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 ~ 85°C |
| 封装/外壳： | 8-WFDFN 裸露焊盘 |
| 包装： | 带卷 (TR) |
LTC3772
APPLICATIO S I FOR ATIO
duty cycle–at its worst case the required R DS(ON) is given
by:
Inductor Core Selection
Once the inductance value is determined, the type of induc-
( I OUT ( MAX ) ) ( 1 + δ P )
R DS ( ON )( DC = 100 %) =
P P
2
tor must be selected. Actual core loss is independent of core
size for a fixed inductor value, but it is very dependent on
inductance selected. As inductance increases, core losses
where P P is the allowable power dissipation and δ P is the
temperature dependency of R DS(ON) . (1 + δ P ) is generally
given for a MOSFET in the form of a normalized R DS(ON) vs
temperature curve, but δ P = 0.005/ ° C can be used as an
approximation for low voltage MOSFETs.
In applications where the maximum duty cycle is less than
100% and the LTC3772 is in continuous mode, the R DS(ON)
is governed by:
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
concentrate on copper loss and preventing saturation.
Ferrite core material saturates “hard,” which means that
inductance collapses abruptly when the peak design cur-
rent is exceeded. This results in an abrupt increase in in-
R DS ( ON ) ?
P P
( DC ) I OUT 2 ( 1 + δ P )
ductor ripple current and consequent output voltage ripple.
Do not allow the core to saturate!
Different core materials and shapes will change the size/
where DC is the maximum operating duty cycle of the
LTC3772.
Inductor Value Calculation
The operating frequency and inductor selection are inter-
related in that higher operating frequencies permit the use
of a smaller inductor for the same amount of inductor ripple
current. However, this is at the expense of efficiency due
to an increase in MOSFET gate charge losses.
The inductance value also has a direct effect on ripple
current. The ripple current, I RIPPLE , decreases with higher
inductance or frequency and increases with higher V IN or
V OUT . The inductor’s peak-to-peak ripple current is given by:
current and price/current relationship of an inductor. Toroid
or shielded pot cores in ferrite or permalloy materials are
small and don’t radiate much energy, but generally cost
more than powdered iron core inductors with similar
characteristics. The choice of which style inductor to use
mainly depends on the price vs size requirements and any
radiated field/EMI requirements. New designs for surface
mount inductors are available from Coiltronics, Coilcraft,
Toko and Sumida.
Output Diode Selection
The catch diode carries load current during the off-time. The
average diode current is therefore dependent on the
P-channel switch duty cycle. At high input voltages the diode
? ?
I RIPPLE =
V IN ? V OUT ? V OUT + V D ?
f ( L ) ? V IN + V D ?
conducts most of the time. As V IN approaches V OUT the
diode conducts only a small fraction of the time. The most
stressful condition for the diode is when the output is short-
where f is the operating frequency. Accepting larger values
of I RIPPLE allows the use of low inductances, but results in
higher output voltage ripple and greater core losses. A
reasonable starting point for setting ripple current is I RIPPLE
= 0.4(I OUT(MAX) ). Remember, the maximum I RIPPLE occurs
circuited. Under this condition the diode must safely handle
I PEAK at close to 100% duty cycle. Therefore, it is impor-
tant to adequately specify the diode peak current and av-
erage power dissipation so as not to exceed the diode
ratings.
at the maximum input voltage.
3772f
11
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相关代理商/技术参数 |
参数描述 |
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| LTC3772ETS8 | 制造商:Linear Technology 功能描述:DC DC Cntrlr Single-OUT Step Down 2.75V to 9.8V Input 8-Pin TSOT-23 |
| LTC3772ETS8#PBF | 制造商:Linear Technology 功能描述:DC DC Cntrlr Single-OUT Step Down 2.75V to 9.8V Input 8-Pin TSOT-23 |
| LTC3772ETS8#TR | 制造商:Linear Technology 功能描述:DC DC Cntrlr Single-OUT Step Down 2.75V to 9.8V Input 8-Pin TSOT-23 T/R |
| LTC3772ETS8#TRM | 制造商:Linear Technology 功能描述:DC DC Cntrlr Single-OUT Step Down 2.75V to 9.8V Input 8-Pin TSOT-23 T/R |
| LTC3772ETS8#TRMPBF | 功能描述:IC REG CTRLR BUCK PWM TSOT23-8 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:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 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:24-WQFN 裸露焊盘 包装:带卷 (TR) |
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