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FB
LM1771
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GND
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Enable
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User's Guide
SNVA163B–July 2006–Revised April 2013
AN-1477 LM1771 Evaluation Board
1 Introduction
The LM1771 is an efficient buck switching controller capable of converting an input voltage between 2.8 V
to 5.5 V into a regulated output voltage as low as 0.8 V. The LM1771 utilizes a constant on-time control
scheme that eliminates the need for external compensation components. The LM1771 features a precision
enable pin to allow for easy sequencing and flexibility in setting the operating range of the power supply.
Three timing options are available, which translates to three possible frequency options for any given
output voltage. Available in the small-sized LLP-6 package, the LM1771 allows for a complete power
supply design to occupy very little board space without sacrificing efficiency.
The LM1771 evaluation board was designed with space critical applications in mind. The entire power
supply occupies less than .86” X .76” on a two layer PCB, but is capable of delivering a maximum
continuous load current of 2A. The output voltage is set at 2.5 V, but can be easily varied by replacing one
of the feedback resistors. The 2000 ns timing option (LM1771U) is used to attain a 378 kHz switching
frequency. The input voltage is nominally 5 V, but can varied over the entire operating range of the
LM1771 (2.8 V to 5.5 V) for testing purposes. At the full 2A load, the efficiency of the power supply is
greater than 92%.
Figure 1. Schematic
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SNVA163B–July 2006–Revised April 2013 AN-1477 LM1771 Evaluation Board
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