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參數(shù)資料
| 型號： | LTC1474 |
| 廠商： | Linear Technology Corporation |
| 英文描述： | Low Quiescent Current High Efficiency Step-Down Converters(低靜態(tài)電流，高效率步降轉(zhuǎn)換器) |
| 中文描述： | 低靜態(tài)電流高效率降壓轉(zhuǎn)換器（低靜態(tài)電流，高效率步降轉(zhuǎn)換器） |
| 文件頁數(shù)： | 12/20頁 |
| 文件大?。?/td> | 296K |
| 代理商： | LTC1474 |
12
LTC1474/LTC1475
APPLICATIO
S I
FOR
ATIO
U
with a built-in internal disconnect. The user needs to
assess his/her application to determine whether this situ-
ation could occur. If so, additional protection is necessary.
Prevention against latchup can be accomplished by sim-
ply connecting a Schottky diode across the SW and V
IN
pins as shown in Figure 8. The diode will normally be
reverse biased unless V
IN
is pulled below V
OUT
at which
time the diode will clamp the (V
OUT
– V
IN
) potential to less
than the 0.6V required for latchup. Note that a low leakage
Schottky should be used to minimize the effect on no-load
supply current. Schottky diodes such as MBR0530, BAS85
and BAT84 work well. Another more serious effect of the
protection diode leakage is that at no load with nothing to
provide a sink for this leakage current, the output voltage
can potentially float above the maximum allowable toler-
ance. To prevent this from occuring, a resistor must be
connected between V
OUT
and ground with a value low
enough to sink the maximum possible leakage current.
W
U
U
Figure 8. Preventing Absolute Maximum
Ratings from Being Exceeded
1474/75 F08
V
IN
V
OUT
LATCHUP
PROTECTION
SCHOTTKY
SW
LTC1474
LTC1475
+
Thermal Considerations
In the majority of the applications, the LTC1474/LTC1475
do not dissipate much heat due to their high efficiency.
However, in applications where the switching regulator is
running at high ambient temperature with low supply
voltage and high duty cycles, such as dropout with the
switch on continuously, the user will need to do some
thermal analysis. The goal of the thermal analysis is to
determine whether the power dissipated by the regulator
exceeds the maximum junction temperature of the part.
The temperature rise is given by:
T
R
= P
θ
JA
where P is the power dissipated by the regulator and
θ
JA
is the thermal resistance from the junction of the die to the
ambient temperature.
The junction temperature is given by:
T
J
= T
A
+ T
R
As an example consider the LTC1474/LTC1475 in dropout
at an input voltage of 3.5V, a load current of 300mA, and
an ambient temperature of 70
°
C. From the typical perfor-
mance graph of switch resistance, the on-resistance of the
P-channel switch at 70
°
C is 3.5
. Therefore, power dissi-
pated by the part is:
P = I
2
R
DS(ON)
= 0.315W
For the MSOP package, the
θ
JA
is 150
°
C/W. Thus the
junction temperature of the regulator is:
T
J
= 70
°
C + (0.315)(150) = 117
°
C
which is near the maximum junction temperature of 125
o
C.
Note that at higher supply voltages, the junction tempera-
ture is lower due to reduced switch resistance.
PC Board Layout Checklist
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of
the LTC1474/LTC1475. These items are also illustrated
graphically in the layout diagram of Figure 9. Check the
following in your layout:
1. Is the Schottky diode cathode closelyconnected to SW
(Pin 5)
2. Is the 0.1
μ
F input decoupling capacitor closelycon-
nected between V
IN
(Pin 7) and ground (Pin 4) This
capacitor carries the high frequency peak currents.
3. When using adjustable version, is the resistive divider
closely connected to the (+) and (–) plates of C
OUT
with
a 10pF capacitor connected across R2
4. Is the 1000pF decoupling capacitor for the current
sense resistor connected as close as possible to Pins 6
and 7 If no current sense resistor is used, Pins 6 and
7 should be shorted.
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| LTC1474CMS8 | 功能描述:IC REG BUCK ADJ 0.75A 8MSOP RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開關(guān)穩(wěn)壓器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- 類型:降壓（降壓） 輸出類型:固定 輸出數(shù):1 輸出電壓:1.2V，1.5V，1.8V，2.5V 輸入電壓:2.7 V ~ 20 V PWM 型:- 頻率 - 開關(guān):- 電流 - 輸出:50mA 同步整流器:是 工作溫度:-40°C ~ 125°C 安裝類型:表面貼裝 封裝/外殼:10-TFSOP，10-MSOP（0.118"，3.00mm 寬）裸露焊盤 包裝:帶卷 (TR) 供應(yīng)商設(shè)備封裝:10-MSOP 裸露焊盤 |
| LTC1474CMS8#PBF | 功能描述:IC REG BUCK ADJ 0.75A 8MSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開關(guān)穩(wěn)壓器 系列:- 產(chǎn)品培訓(xùn)模塊:MIC23xxx HyperLight Load™ Regulators 標(biāo)準(zhǔn)包裝:5,000 系列:HyperLight Load® 類型:降壓（降壓） 輸出類型:固定 輸出數(shù):1 輸出電壓:1.8V 輸入電壓:2.7 V ~ 5.5 V PWM 型:混合物 頻率 - 開關(guān):4MHz 電流 - 輸出:2A 同步整流器:是 工作溫度:-40°C ~ 125°C 安裝類型:表面貼裝 封裝/外殼:8-VFDFN 裸露焊盤，8-MLF? 包裝:帶卷 (TR) 供應(yīng)商設(shè)備封裝:8-MLF?（2x2） 產(chǎn)品目錄頁面:1094 (CN2011-ZH PDF) 其它名稱:576-3303-2 |
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