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| 型号： | LT3508IUF#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 8/26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
OPERATION
The LT3508 is a dual constant frequency, current mode
regulator with internal power switches. Operation can be
best understood by referring to the Block Diagram. If the
SHDN pin is tied to ground, the LT3508 is shut down and
draws minimal current from the input source tied to the
V IN pins. If the SHDN pin exceeds 1V, the internal bias
circuits turn on, including the internal regulator, reference
and oscillator. The switching regulators will only begin to
operate when the SHDN pin exceeds 2.63V.
The switcher is a current mode regulator. Instead of directly
modulating the duty cycle of the power switch, the feedback
loop controls the peak current in the switch during each
cycle. Compared to voltage mode control, current mode
control improves loop dynamics and provides cycle-by-
cycle current limit. A pulse from the oscillator sets the
RS ?ip-?op and turns on the internal NPN power switch.
Current in the switch and the external inductor begins to
increase. When this current exceeds a level determined
by the voltage at V C , current comparator C1 resets the
?ip-?op, turning off the switch. The current in the inductor
?ows through the external Schottky diode and begins to
decrease. The cycle begins again at the next pulse from the
oscillator. In this way, the voltage on the V C pin controls
the current through the inductor to the output. The internal
error ampli?er regulates the output current by continually
adjusting the V C pin voltage. The threshold for switching
on the V C pin is 0.8V, and an active clamp of 1.75V limits
the output current.
The switching frequency is set either by the resistance to
GND at the RT/SYNC pin or the frequency of the logic-level
signal driving the RT/SYNC pin. A detection circuit monitors
between the two modes. Unique circuitry generates the
appropriate slope compensation ramps and generates the
180° out-of-phase clocks for the two channels.
The switching regulator performs frequency foldback
during overload conditions. An ampli?er senses when
V FB is less than 0.625V and begins decreasing the oscil-
lator frequency down from full frequency to 12% of the
nominal frequency when V FB = 0V. The FB pin is less than
0.8V during start-up, short-circuit and overload conditions.
Frequency foldback helps limit switch current under these
conditions.
The switch driver operates either from V IN or from the
BOOST pin. An external capacitor and Schottky diode are
used to generate a voltage at the BOOST pin that is higher
than the input supply. This allows the driver to saturate the
internal bipolar NPN power switch for ef?cient operation.
The TRACK/SS pin serves as an alternative input to the
error ampli?er. The ampli?er will use the lowest voltage of
either the reference of 0.8V or the voltage on the TRACK/
SS pin as the positive input of error ampli?er. Since the
TRACK/SS pin is driven by a constant current source, a
single capacitor on the pin will generate a linear ramp on
the output voltage. Tying the TRACK/SS pin to a resistor
divider from the output of one of the switching regulators
allows one output to track another.
The PG output is an open-collector transistor that is off
when the output is in regulation, allowing an external re-
sistor to pull the PG pin high. Power good is valid when
the LT3508 is enabled ( SHDN is high) and V IN1 is greater
than 3.7V.
for the presence of a SYNC signal on the pin and switches
3508fd
8
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LT3509 | 制造商:LINER 制造商全称:Linear Technology 功能描述:36V 500mA Step-Down Regulator and 200mA LDO |
| LT3509EDE#PBF | 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:250 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V 输入电压:2.05 V ~ 6 V PWM 型:电压模式 频率 - 开关:2MHz 电流 - 输出:500mA 同步整流器:是 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:6-UFDFN 包装:带卷 (TR) 供应商设备封装:6-SON（1.45x1） 产品目录页面:1032 (CN2011-ZH PDF) 其它名称:296-25628-2 |
| 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 |
| LT3509EDEPBF | 制造商:Linear Technology 功能描述:Sw. Regulator Dual 700mA 3.6-36V DFN14EP |
| LT3509EDE-PBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Dual 36V, 700mA Step-Down Regulator |
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