Linear 公司的LTCR3805-5是可调频率电流模式反激/升压/SEPIC DC/DC控制器，工作频率（70kHz-700kHz）和斜率补偿由外接电阻编程，输出电压精度±1.5%，主要用在汽车电源，通信电源，隔离的电子设备，家用电器电源和PoE。本文介绍了LTCR3805-5主要特性，方框图，多种应用电路以及评估板电路图和材料清单。

Adjustable Frequency Current Mode Flyback/ Boost/SEPIC DC/DC Controller

The LTCR3805-5 is a current mode DC/DC controller designed to drive an N-channel MOSFET in flyback, boost and SEPIC converter applications. Operating frequency and slope compensation can be programmed by external resistors. Programmable overcurrent sensing protects the converter from overload and short-circuit conditions.

Soft-start can be programmed using an external capacitor and the soft-start capacitor also programs an automatic restart feature.

The LTC3805-5 provides ±1.5% output voltage accuracy and consumes only 360μA of quiescent current during normal operation and only 40μA during micropower startup. Using a 9.5V internal shunt regulator, the LTC3805-5 can be powered from a high VIN through a resistor or it can be powered directly from a low impedance DC voltage from 4.7V to 8.8V.

The LTC3805-5 is available in the 10-lead MSOP package and the 3mmx3mm DFN package.

LTCR3805-5主要特性：

VIN and VOUT Limited Only by External Components

4.5V Undervoltage Lockout Threshold

Adjustable Slope Compensation

Adjustable Overcurrent Protection with Automatic Restart

Adjustable Operating Frequency (70kHz to 700kHz) With One External Resistor

Synchronizable to an External Clock

±1.5% Reference Accuracy

Only 100mV Current Sense Voltage Drop

RUN Pin with Precision Threshold and Adjustable Hysteresis

Programmable Soft-Start with One External Capacitor

Low Quiescent Current: 360μA

Small 10-Lead MSOP and 3mm x3mm DFN

LTCR3805-5应用：

Automotive Power Supplies

Telecom Power Supplies

Isolated Electronic Equipment

Auxiliary/Housekeeping Power Supplies

Power over Ethernet

图1。LTCR3805-5方框图

图2。LTCR3805-5 5.5V-40V输入12V/2A输出SEPIC转换器电路图

图3。LTCR3805-5隔离通信电源18V-72V输入3.3V/3A输出电路图演示板1576

Demonstration circuit 1576 is high efficiency nonisolated SEPIC (Single Ended Primary Inductor Converter) converter featuring the LTC3805-5 switching controller. The DC1576 converts 5V to 30V input to 12V output and provides over 3A of output current.

The converter operates at 300kHz with efficiency over 90%. With proper amount of airflow, the DC1576 converter can generate over 3A of output current. The DC1576 can be easily modified to generate output voltages in the range from 0.8V to 48V.

Also, the DC1576 can be modified for other input voltages like 5V-36V, 9V-36V, 36V-72V, and so on. The wider input voltage range will decrease the converter efficiency. Therefore, narrow input voltage range will be more desirable.

The LTC3805-5 can be synchronized to an external clock of up to 400kHz. Please refer to LTC3805-5 data sheet for design details and applications information.


图4。演示板1576电路图
演示板1576材料清单：

详情请见：
http://cds.linear.com/docs/Datasheet/38055fd.pdf
和
http://cds.linear.com/docs/Demo%20Board%20Manual/dc1576A.pdf