1FEATURES

2• Input Voltage Range of 2.8V to 5.5V

• 0.8V Reference Voltage

• No Compensation Required

• Constant Frequency Across Input Range

• Low Quiescent Current of 400μA

• Internal Soft-start

• Short Circuit Protection

• 5-Pin SOT-23 Package

APPLICATIONS

• Simple To Design, High Efficiency Step Down

Switching Regulators

• Set-Top Boxes

• Cable Modems

• Printers

• Digital Video Recorders

• Servers

DESCRIPTION

The LM1770 is an efficient synchronous buck

switching controller in a tiny SOT-23 package. The

constant on-time control scheme provides a simple

design free of compensation components, allowing

minimal component count and board space. It also

incorporates a unique input feed-forward to maintain a constant frequency independent of the input

voltage. The LM1770 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 LM1770 are available depending on the switching frequency desired for the

application. Nominal switching frequencies are in the

range of 100kHz to 1000kHz.