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| 型号： | LT3990IDD#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 14/22页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK ADJ 0.35A 10DFN |
| 标准包装： | 2,500 |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 1.21 V ~ 25 V |
| 输入电压： | 4.2 V ~ 62 V |
| PWM 型： | 电流模式，Burst Mode? |
| 频率 - 开关： | 210kHz ~ 2.3MHz |
| 电流 - 输出： | 350mA |
| 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： | 10-WFDFN 裸露焊盘 |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 10-DFN（3x3） |
LT3990/LT3990-3.3/LT3990-5
APPLICATIONS INFORMATION
BD
V OUT
5.0
FRONT PAGE APPLICATION
V OUT = 3.3V
V IN
V IN
BOOST
4.5
LT3990
SW
C3
4.0
TO START
TO RUN
GND
3.5
(4a) For V OUT ≥ 2.2V
3.0
V IN
V IN
BD
BOOST
LT3990
SW
GND
C3
V OUT
2.5
6.5
6.0
0 50 100 150 200 250
LOAD CURRENT (mA)
FRONT PAGE APPLICATION
V OUT = 5V, f = 600kHz
TO START
300
350
3990 F04
(4b) For V OUT < 2.2V; V IN < 30V
5.5
TO RUN
V UVLO =
R3 + R4
Figure4.TwoCircuitsforGeneratingtheBoostVoltage
the boost capacitor is charged with the energy stored
in the inductor, the circuit will rely on some minimum
load current to get the boost circuit running properly.
This minimum load will depend on input and output volt-
ages, and on the arrangement of the boost circuit. The
minimum load generally goes to zero once the circuit has
started. Figure 5 shows a plot of minimum load to start
and to run as a function of input voltage. In many cases
the discharged output capacitor will present a load to the
switcher, which will allow it to start. The plots show the
worst-case situation where V IN is ramping very slowly.
For lower start-up voltage, the boost diode can be tied to
V IN ; however, this restricts the input range to one-half of
the absolute maximum rating of the BOOST pin.
Enable and Undervoltage Lockout
The LT3990 is in shutdown when the EN/UVLO pin is low
and active when the pin is high. The rising threshold of the
EN/UVLO comparator is 1.19V, with a 35mV hysteresis.
This threshold is accurate when V IN is above 4.2V. If V IN
is lower than 4.2V, tie EN/UVLO pin to GND to place the
part in shutdown.
Figure 6 shows how to add undervoltage lockout (UVLO)
to the LT3990. Typically, UVLO is used in situations where
the input supply is current limited, or has a relatively high
5.0
4.5
4.0
0 50 100 150 200 250 300 350
LOAD CURRENT (mA) 3990 F05
Figure 5. The Minimum Input Voltage Depends on
Output Voltage, Load Current and Boost Circuit
source resistance. A switching regulator draws constant
power from the source, so source current increases as
source voltage drops. This looks like a negative resistance
load to the source and can cause the source to current limit
or latch low under low source voltage conditions. UVLO
prevents the regulator from operating at source voltages
where the problems might occur. The UVLO threshold can
be adjusted by setting the values R3 and R4 such that they
satisfy the following equation:
? 1.19V
R4
where switching should not start until V IN is above V UVLO .
Note that due to the comparator’s hysteresis, switching
will not stop until the input falls slightly below V UVLO .
Undervoltage lockout is functional only when V UVLO is
greater than 5V.
3990fa
14
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相关代理商/技术参数 |
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| LT3990IMS | 制造商:LINER 制造商全称:Linear Technology 功能描述:60V, 350mA Step-Down Regulator with 2.5μA Quiescent Current and Integrated Diodes |
| LT3990IMSE#PBF | 功能描述:IC REG BUCK ADJ 0.35A 16MSOP 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 |
| LT3990IMSE#TRPBF | 功能描述:IC REG BUCK ADJ 0.35A 16MSOP 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 |
| LT3990IMSE-3.3#PBF | 功能描述:IC REG BUCK ADJ 0.35A 16MSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 产品培训模块:MIC23xxx HyperLight Load™ Regulators 标准包装:5,000 系列:HyperLight Load® 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.8V 输入电压:2.7 V ~ 5.5 V PWM 型:混合物 频率 - 开关:4MHz 电流 - 输出:2A 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:8-VFDFN 裸露焊盘，8-MLF? 包装:带卷 (TR) 供应商设备封装:8-MLF?（2x2） 产品目录页面:1094 (CN2011-ZH PDF) 其它名称:576-3303-2 |
| LT3990IMSE-3.3#TRPBF | 功能描述:IC REG BUCK ADJ 0.35A 16MSOP 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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