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| 型号： | LT3508IUF#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 13/26页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK ADJ 1.4A DL 24QFN |
| 标准包装： | 2,500 |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 2 |
| 输出电压： | 0.8 V ~ 35.3 V |
| 输入电压： | 3.7 V ~ 36 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 920kHz ~ 1.06MHz |
| 电流 - 输出： | 1.4A |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 125°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 24-WFQFN 裸露焊盘 |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 24-QFN 裸露焊盘（4x4） |
LT3508
APPLICATIONS INFORMATION
I OUT ( V IN – V OUT )
Diode Selection
The catch diode (D1 from Figure 1) conducts current only
during switch off time. Average forward current in normal
operation can be calculated from:
I D(AVG) =
V IN
The only reason to consider a diode with a larger current
rating than necessary for nominal operation is for the
worst-case condition of shorted output. The diode cur-
rent will then increase to the typical peak switch current.
Peak reverse voltage is equal to the regulator input voltage.
Use a diode with a reverse voltage rating greater than the
input voltage. Table 4 lists several Schottky diodes and their
and higher, the standard circuit (Figure 4a) is best. For
outputs between 2.8V and 3.3V, use a small Schottky
diode (such as the BAT-54). For lower output voltages,
the boost diode can be tied to the input (Figure 4b). The
circuit in Figure 4a is more ef?cient because the boost pin
current comes from a lower voltage source. Finally, the
anode of the boost diode can be tied to another source
(V AUX ) that is at least 3V (Figure 4c). For example, if you
are generating a 3.3V output, and the 3.3V output is on
whenever the particular channel is on, the anode of the
BOOST diode can be connected to the 3.3V output. In any
case, be sure that the maximum voltage at the BOOST pin
is both less than 60V and the voltage difference between
the BOOST and SW pins is less than 30V.
D2
manufacturers. If operating at high ambient temperatures,
consider using a Schottky with low reverse leakage.
BOOST
LT3508
C3
Table 4. Schottky Diodes
V IN
V IN
SW
V OUT
PART NUMBER
On Semiconductor
MBR0520L
MBR0540
MBRM120E
V R
(V)
20
40
20
I AVE
(A)
0.5
0.5
1
V F at 1A
(mV)
620
530
V F at 2A
(mV)
GND
V BOOST – V SW ? V OUT
MAX V BOOST ? V IN + V OUT
(4a)
D2
MBRM140
40
1
550
BOOST
C3
Diodes Inc.
LT3508
B0530W
B120
30
20
0.5
1
500
V IN
V IN
GND
SW
V OUT
B130
30
1
500
B140HB
DFLS140
B240
40
40
40
1
1.1
2
510
500
V BOOST – V SW ? V IN
MAX V BOOST ? 2V IN
D2
(4b)
BOOST Pin Considerations
V AUX > 3V
BOOST
C3
The capacitor and diode tied to the BOOST pin generate
a voltage that is higher than the input voltage. In most
V IN
V IN
LT3508
SW
V OUT
cases, a 0.22μF capacitor and fast switching diode (such
as the CMDSH-3 or MMSD914LT1) will work well. For ap-
GND
plications 1MHz or faster, a 0.1μF capacitor is suf?cient.
Use a 0.47μF capacitor or greater for applications running
below 500kHz. Figure 4 shows three ways to arrange the
boost circuit. The BOOST pin must be more than 2.5V
V BOOST – V SW ? V AUX
MAX V BOOST ? V AUX + V IN
MINIMUM VALUE FOR V AUX = 3V
(4c)
3508 F04
above the SW pin for full ef?ciency. For outputs of 3.3V
Figure 4. Generating the Boost Voltage
3508fd
13
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| LT3509EDE#TRPBF | 功能描述:IC REG BUCK ADJ 0.7A DL 14DFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:2,500 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V，1.5V，1.8V，2.5V 输入电压:2.7 V ~ 20 V PWM 型:- 频率 - 开关:- 电流 - 输出:50mA 同步整流器:是 工作温度:-40°C ~ 125°C 安装类型:表面贴装 封装/外壳:10-TFSOP，10-MSOP（0.118"，3.00mm 宽）裸露焊盘 包装:带卷 (TR) 供应商设备封装:10-MSOP 裸露焊盘 |
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