Features

• No Sense Resistor Required
• True Current Mode Control
• Optimized for High Step-Down Ratios
• t_ON(MIN) <=100ns
• Extremely Fast Transient Response
• Stable with Ceramic C_OUT
• Dual N-Channel MOSFET Synchronous Drive
• Power Good Output Voltage Monitor (LTC1778)
• Adjustable On-Time (LTC1778-1)
• Wide V_IN Range: 4V to 36V
• ±1% 0.8V Voltage Reference
• Adjustable Current Limit
• Adjustable Switching Frequency
• Programmable Soft-Start
• Output Overvoltage Protection
• Optional Short-Circuit Shutdown Timer
• Micropower Shutdown: I_Q <30µA
• Available in a 16-Pin Narrow SSOP Package

Typical Application

Description

The LTC1778 is a synchronous stepdown switching regulator controller optimized for CPU power. The controller uses a valley current control architecture to deliver very low duty cycles with excellent transient response without requiring a sense resistor. Operating frequency is selected by an external resistor and is compensated for variations in V_IN.

Discontinuous mode operation provides high efficiency operation at light loads. A forced continuous control pin reduces noise and RF interference, and can assist secondary winding regulation by disabling discontinuous operation when the main output is lightly loaded.

Fault protection is provided by internal foldback current limiting, an output overvoltage comparator and optional short-circuit shutdown timer. Soft-start capability for supply sequencing is accomplished using an external timing capacitor. The regulator current limit level is user programmable. Wide supply range allows operation from 4V to 36V at the input and from 0.8V up to (0.9)V_IN at the output.