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参数资料
| 型号： | LTC3772EDDB#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 10/20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
The basic LTC3772 application circuit is shown on the front
page of this data sheet. External component selection is
driven by the load requirement and begins with the selec-
tion of the power MOSFET inductor and the output diode.
These are selected followed by the input bypass capacitor
However, for operation above 20% duty cycle, slope com-
pensation has to be taken into consideration to select the
appropriate value of R DS(ON) to provide the required amount
of load current:
C IN and output bypass capacitor C OUT .
Power MOSFET Selection
R DS ( ON )( MAX ) =
5 ? V SENSE ( MAX ) – SF
?
6 I OUT ( MAX )
An external P-channel power MOSFET must be selected for
use with the LTC3772. The main selection criteria for the
power MOSFET are the threshold voltage V GS(TH) and the
“on” resistance R DS(ON) , reverse transfer capacitance C RSS
and total gate charge.
Since the LTC3772 is designed for operation down to low
input voltages, a sublogic level threshold MOSFET (R DS(ON)
guaranteed at V GS = 2.5V) is required for applications that
where SF is a factor whose value is obtained from the curve
in Figure 1.
These must be further derated to take into account the
significant variation in on-resistance with temperature. The
following equation is a good guide for determining the
required R DS(ON)MAX at 25 ° C (manufacturer’s specifica-
tion), allowing some margin for variations in the LTC3772
and external component values:
work close to this voltage. When these MOSFETs are used,
make sure that the input supply to the LTC3772 is less than
the absolute maximum V GS rating.
R DS ( ON )( MAX ) =
5
6
? 0 . 9 ?
? V SENSE ( MAX ) – SF
I OUT ( MAX ) ? ρ T
The P-channel MOSFET’s on-resistance is chosen based on
the required load current. The maximum average output
load current I OUT(MAX) is equal to the peak inductor current
minus half the peak-to-peak ripple current I RIPPLE . The
LTC3772’s current comparator monitors the drain-to-
source voltage V DS of the P-channel MOSFET, which is
sensed between the V IN and SW pins. The peak inductor
current is limited by the current threshold, set by the volt-
age on the I TH pin of the current comparator. The voltage
on the I TH pin is internally clamped, which limits the maxi-
mum current sense threshold ? V SENSE(MAX) to approxi-
mately 175mV when I PRG is floating (100mV when I PRG is
tied low; 250mV when I PRG is tied high).
The output current that the LTC3772 can provide is given by:
The ρ T is a normalizing term accounting for the tempera-
ture variation in on-resistance, which is typically about
0.4%/ ° C, as shown in Figure 2. Junction to case tempera-
ture T JC is about 10 ° C in most applications. For a maximum
ambient temperature of 70 ° C, using ρ 80 ° C ~ 1.3 in the above
equation is a reasonable choice.
The required minimum R DS(ON) of the MOSFET is also
governed by its allowable power dissipation. For applica-
tions that may operate the LTC3772 in dropout–i.e., 100%
2.0
1.5
– RIPPLE
I OUT ( MAX ) =
? V SENSE ( MAX )
R DS ( ON )
I
2
1.0
A reasonable starting point is setting ripple current I RIPPLE
to be 40% of I OUT(MAX) . Rearranging the above equation
0.5
5 ? V SENSE ( MAX )
yields:
R DS ( ON )( MAX )
=
6 I OUT ( MAX )
?
0
– 50
0 50 100
JUNCTION TEMPERATURE ( ? C)
150
3772 F02
for Duty Cycle < 20%.
Figure 2. R DS(ON) vs Temperature
3772f
10
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相关代理商/技术参数 |
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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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