LM1771 Low-Voltage Synchronous Buck Controller with Precision Enable and No External
Compensation
October 2006
LM1771
Low-Voltage Synchronous Buck Controller with
Precision Enable and No External Compensation
General Description
The LM1771 is an efficient synchronous buck switching con-
troller with a precision enable requiring no external compen-
sation. The constant on-time control scheme provides a
simple design free of compensation components, allowing
minimal component count and board space. The precision
enable pin allows flexibility in sequencing multiple rails and
setting UVLO. The LM1771 also incorporates a unique input
feed-forward to maintain a constant frequency independent
of the input voltage. The LM1771 is optimized for a low
voltage input range of 2.8V to 5.5V and can provide an
adjustable output as low as 0.8V. Driving an external high
side PFET and low side NFET it can provide efficiencies as
high as 95%.
Three versions of the LM1771 are available depending on
the switching frequency desired for the application. Nominal
switching frequencies are in the range of 100kHz to
1000kHz.
Features
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Input voltage range of 2.8V to 5.5V
0.8V reference voltage
Precision enable
No compensation required
Constant frequency across input range
Low quiescent current of 400 µA
Internal soft-start
Short circuit protection
Tiny LLP-6 package and MSOP-8 package
Applications
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Simple To Design, High Efficiency Step Down Switching
Regulators
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FPGAs, DSPs, and ASIC Power Supplies
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Set-Top Boxes
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Cable Modems
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Printers
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Digital Video Recorders
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Servers
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Graphic Cards
Typical Application Circuit
20189001
© 2006 National Semiconductor Corporation
DS201890
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