Features

• Ultralow Quiescent Current:
  2.7μA I_Q at 12V_IN to 3.3V_OUT
• Low Ripple Burst Mode® Operation
  Output Ripple < 15mV_P-P
• Wide Input Range: Operation from 4.3V to 42V
• 2.5A Maximum Output Current
• Excellent Start-Up and Dropout Performance
• Adjustable Switching Frequency: 200kHz to 2MHz
• Synchronizable Between 250kHz to 2MHz
• Accurate Programmable Undervoltage Lockout
• Low Shutdown Current: I_Q = 700nA
• Power Good Flag
• Soft-Start Capability
• Thermal Shutdown Protection
• Current Limit Foldback with Soft-Start Override
• Saturating Switch Design: 75mΩ On Resistance
• Small, Thermally Enhanced 16-Lead MSOP Package

Typical Application

Description

The LT®3975 is an adjustable frequency monolithic buck switching regulator that accepts a wide input voltage range up to 42V. Low quiescent current design consumes only 2.7μA of supply current while regulating with no load. Low ripple Burst Mode operation maintains high efficiency at low output currents while keeping the output ripple below 15mV in a typical application. The LT3975 can supply up to 2.5A of load current and has current limit foldback to limit power dissipation during short circuit. A low dropout voltage of 500mV is maintained when the input voltage drops below the programmed output voltage, such as during automotive cold crank.

An internally compensated current mode topology is used for fast transient response and good loop stability. A high efficiency 75mΩ switch is included on the die along with a boost Schottky diode and the necessary oscillator, control, and logic circuitry. An accurate 1.02V threshold enable pin can be driven directly from a microcontroller or used as a programmable undervoltage lockout. A capacitor on the SS pin provides a controlled inrush current (soft-start). A power good flag signals when V_OUT reaches 91.6% of the programmed output voltage. The LT3975 is available in a small 16-lead MSOP package with exposed pad for low thermal resistance.