Features

• Wide Input Range: 3.3V to 60V
• 1.5A Peak Switch Current
• Burst Mode Operation: 100µA Quiescent Current**
• Low Shutdown Current: I_Q < 1µA
• Power Good Flag with Programmable Threshold
• Load Dump Protection to 60V
• 500kHz Switching Frequency
• Saturating Switch Design: 0.2 Ohm On-Resistance
• Peak Switch Current Maintained Over Full Duty Cycle Range*
• 1.25V Feedback Reference Voltage
• Easily Synchronizable
• Soft-Start Capability
• Small 16-Pin Thermally Enhanced TSSOP Package

Typical Application

Description

The LT1977 is a 500kHz monolithic buck switching regulator that accepts input voltages up to 60V. A high efficiency 1.5A, 0.2Ω switch is included on the die along with all the necessary oscillator, control and logic circuitry. Current mode topology is used for fast transient response and good loop stability.

Innovative design techniques along with a new high voltage process achieve high efficiency over a wide input range. Efficiency is maintained over a wide output current range by employing Burst Mode operation at low currents, utilizing the output to bias the internal circuitry, and by using a supply boost capacitor to fully saturate the power switch. Patented circuitry maintains peak switch current over the full duty cycle range.* Shutdown reduces input supply current to less than 1µA. External synchronization can be implemented by driving the SYNC pin with logic-level inputs. A single capacitor from the C_SS pin to the output provides a controlled output voltage ramp (soft-start). The device also has a power good flag with a programmable threshold and time-out and thermal shutdown protection.

The LT1977 is available in a 16-pin TSSOP package with exposed pad leadframe for low thermal resistance. The LT1976, a 200kHz reduced switch frequency version of the LT1977, is also available. See the Applications Information section for selection criteria between the LT1976 and LT1977.

*U.S. Patent 6,498,466 and 6,531,909
**See Burst Mode Operation section for conditions