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参数资料
| 型号： | LT3509EDE#TRPBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 1.2 A DUAL SWITCHING CONTROLLER, 2500 kHz SWITCHING FREQ-MAX, PDSO14 |
| 封装： | 4 X 3 MM, LEAD FREE, PLASTIC, MO-229WGED-3, DFN-14 |
| 文件页数： | 23/24页 |
| 文件大小： | 271K |
| 代理商： | LT3509EDE#TRPBF |
LT3509
8
3509fc
OPERATION
Overview
The LT3509 is a dual, constant frequency, current mode
switching regulator with internal power switches. The two
independent channels share a common voltage reference
andoscillatorandoperateinphase.Theswitchingfrequency
is set by a single resistor and can also be synchronized to
an external clock. Operation can be best understood by
referring to the Block Diagram (Figure 1).
Startup and Shutdown
When the RUN/SS[1,2] pins are pulled low (<0.4V) the
associated regulator channel is shut down. If both channels
are shut down, the common circuitry also enters a low
current state. When the RUN/SS pins exceed approximately
0.8V, the common circuitry and the associated regulator
are enabled but the output current is limited. From 0.8V
up to 2.0V the current limit increases until it reaches the
full value. The RUN/SS pins also incorporate a 1μA pull-
up to approximately 3V, so the regulator will run if they
are left open. A capacitor to ground will cause a current
limited soft-start to occur at power-up. In the case of
undervoltage, overvoltage or overtemperature conditions
the internal circuitry will pull the RUN/SS pins down with
a current of approximately 250μA. Thus a new soft-start
cycle will occur when the fault condition ends.
Voltage and Current Regulation
The power switches are controlled by a current-mode
regulator architecture. The power switch is turned on at
the beginning of each clock cycle and turned off by the
main current comparator. The inductor current will ramp
up while the switch is on until it reaches the peak current
threshold. The current at which it turns off is determined
by the error amp and the internal compensation network.
When the switch turns off, the current in the inductor
will cause the SW pin to fall rapidly until the catch diode,
D1, conducts. The voltage applied to the inductor will
now reverse and the current will linearly fall. The resistor
divider, R1 and R2, sets the desired output voltage such
that when the voltage at FB reaches 0.8V, the main current
comparator threshold will fall and reduce the peak inductor
current and hence the average current, until it matches the
load current. By making current the controlled variable in
the loop, the inductor impedance is effectively removed
from the transfer function and the compensation network
is simplied. The main current comparator threshold is
reduced by the slope compensation signal to eliminate
sub-harmonic oscillations at duty cycles >50%.
Current Limiting
Current mode control provides cycle-by-cycle current
limiting by means of a clamp on the maximum current that
can be provided by the switch. A comparator monitors the
current owing through the catch diode via the DA pin.
This comparator delays switching if the diode current is
higher than 0.95A (typical). This current level is indicative
of a fault condition such as a shorted output with a high
input voltage. Switching will only resume once the diode
current has fallen below the 0.95A limit. This way the DA
comparator regulates the valley current of the inductor to
0.95A during a short circuit. This will ensure the part will
survive a short-circuit event.
Over and Undervoltage Shutdown
A basic undervoltage lockout prevents switching if VIN
is below 3.3V (typical). The overvoltage shutdown stops
the part from switching when VIN is greater than 38.5V
(typical). This protects the device and its load during
momentary overvoltage events. After the input voltage
falls below 38.5V, the part initiates a soft start sequence
and resumes switching.
BOOST Circuit
To ensure best efciency and minimum dropout voltage
the output transistor base drive is boosted above VIN by
the external boost capacitors (C4). When the SW pin is
low the capacitors are charged via the BOOST diodes and
the supply on BD.
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LT3509EMSE#PBF | 功能描述:IC REG BUCK ADJ 0.7A DL 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: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 |
| LT3509EMSE#TRPBF | 功能描述:IC REG BUCK ADJ 0.7A DL 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 |
| LT3509EMSEPBF | 制造商:Linear Technology 功能描述:Conv DC-DC Dual Step-Down 3.6-36V MSOP16 |
| LT3509EMSE-PBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Dual 36V, 700mA Step-Down Regulator |
| LT3509EMSE-TRPBF | 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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