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參數資料
| 型號： | LTC1779 |
| 廠商： | Linear Technology Corporation |
| 英文描述： | 250mA Low Dropout Current Mode Step-Down DC/DC Converter in SOT-23(2.5V輸出,250mA電流模式，低壓差,步降DC/DC變換器（SOT-23封裝）) |
| 中文描述： | 250mA的低壓差電流模式降壓DC / DC轉換器采用SOT - 23（2.5V的輸出，250mA的電流模式，低壓差，步降直流/直流變換器（采用SOT - 23封裝）） |
| 文件頁數： | 6/12頁 |
| 文件大?。?/td> | 174K |
| 代理商： | LTC1779 |
6
LTC1779
The basic LTC1779 application circuit is shown in Figure
1. External component selection is driven by the load
requirement and begins with the selection of L1 and
R
SENSE
(= R1). Next, the output diode D1 is selected
followed by C
IN
(= C1)and C
OUT
(= C2).
R
SENSE
Selection for Output Current
R
SENSE
is chosen based on the required output current.
With the current comparator monitoring the voltage devel-
oped across R
SENSE
, the threshold of the comparator
determines the inductor’s peak current. The output cur-
rent the LTC1779 can provide is given by:
I
M
R
I
OUT
SENSE
RIPPLE
2
=
+
2
0 12
.
where I
RIPPLE
is the inductor peak-to-peak ripple current
(see Inductor Value Calculation section) and M is as
defined in the previous section and in Figure 3.
A reasonable starting point for setting ripple current is
I
RIPPLE
= (0.4)(I
OUT
). Rearranging the above equation, it
becomes:
R
M
I
SENSE
OUT
=
10
–2
for Duty Cycle<40%
where I
OUT
is in amps.
However, for operation that is above 40% duty cycle, slope
compensation effect has to be taken into consideration to
select the appropriate value to provide the required amount
of current. Using Figure 2, the value of R
SENSE
is:
R
M
I
SF
100
SENSE
OUT
=
10
2
–
where SF is the slope factor from Figure 2 in percent.
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:
I
V
V
f L
V
V
V
V
RIPPLE
IN
OUT
OUT
IN
D
D
=
+
+
(Refer to Functional Diagram)
OPERATIOU
The variable M is the ratio of the total switch current to that
portion of the switch current that flows through R
SENSE
. M
is a function of both R
SENSE
and R
OUT
of the internal power
switch, which in turn, is a strong function of supply
voltage. For values of M refer to Figure 3. In order to
guarantee the desired I
PK
over the full range of supply
voltage, the minimum value of M, corresponding to the
minimum supply voltage seen in the application, should
be chosen. Note that the selection of R
SENSE
, and hence
the resulting M, is an iterative process. For most applica-
tions, a value of R
SENSE
between 0
and 20
will be
chosen.
Figure 3. M vs Supply Voltage
APPLICATIOU
W
U
U
SUPPLY VOLTAGE (V)
0
M
60
55
50
45
40
35
30
25
20
8
1779 F03
2
4
6
10
7
1
3
5
9
R
SENSE
= 0
R
SENSE
= 2
R
SENSE
= 18.2
I
OUT
= 100mA
R
SENSE
= 14
R
SENSE
= 10
R
SENSE
= 6.2
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相關代理商/技術參數 |
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|---|---|
| LTC1779ES6#PBF | 制造商:Linear Technology 功能描述:Conv DC-DC Single Step Down 2.5V to 9.8V 6-Pin TSOT-23 制造商:Linear Technology 功能描述:DP-SWREG/Monolithic, CUT TAPE 500mA, 500kHz Step-Down Switching Regulator |
| LTC1779ES6#TR | 功能描述:IC REG BUCK ADJ 0.25A SOT23-6 RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開關穩(wěn)壓器 系列:- 標準包裝:2,500 系列:- 類型:升壓（升壓） 輸出類型:可調式 輸出數:1 輸出電壓:1.24 V ~ 30 V 輸入電壓:1.5 V ~ 12 V PWM 型:電流模式，混合 頻率 - 開關:600kHz 電流 - 輸出:500mA 同步整流器:無 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:8-SOIC（0.154"，3.90mm 寬） 包裝:帶卷 (TR) 供應商設備封裝:8-SOIC |
| LTC1779ES6#TRM | 功能描述:IC REG BUCK ADJ 0.25A SOT23-6 RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開關穩(wěn)壓器 系列:- 標準包裝:2,500 系列:- 類型:升壓（升壓） 輸出類型:可調式 輸出數:1 輸出電壓:1.24 V ~ 30 V 輸入電壓:1.5 V ~ 12 V PWM 型:電流模式，混合 頻率 - 開關:600kHz 電流 - 輸出:500mA 同步整流器:無 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:8-SOIC（0.154"，3.90mm 寬） 包裝:帶卷 (TR) 供應商設備封裝:8-SOIC |
| LTC1779ES6#TRMPBF | 功能描述:IC REG BUCK ADJ 0.25A SOT23-6 RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開關穩(wěn)壓器 系列:- 產品培訓模塊:High Efficiency Current Mode Switching Regulators CMOS LDO Regulators 特色產品:BD91x Series Step-Down Regulators 標準包裝:2,500 系列:- 類型:降壓（降壓） 輸出類型:兩者兼有 輸出數:2 輸出電壓:3.3V，0.8 V ~ 2.5 V 輸入電壓:4.5 V ~ 5.5 V PWM 型:電流模式 頻率 - 開關:1MHz 電流 - 輸出:1.5A 同步整流器:是 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:20-VFQFN 裸露焊盤 包裝:帶卷 (TR) 供應商設備封裝:VQFN020V4040 產品目錄頁面:1373 (CN2011-ZH PDF) 其它名稱:BD9152MUV-E2TR |
| LTC1779ES6#TRPBF | 功能描述:IC REG BUCK ADJ 0.25A SOT23-6 RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開關穩(wěn)壓器 系列:- 標準包裝:2,500 系列:- 類型:升壓（升壓） 輸出類型:可調式 輸出數:1 輸出電壓:1.24 V ~ 30 V 輸入電壓:1.5 V ~ 12 V PWM 型:電流模式，混合 頻率 - 開關:600kHz 電流 - 輸出:500mA 同步整流器:無 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:8-SOIC（0.154"，3.90mm 寬） 包裝:帶卷 (TR) 供應商設備封裝:8-SOIC |
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