Microsemi Corporation LX1553IM

Description
The LX155x family of ultra-low start-up current (250µA max) current mode control ICs offers new levels of energy efficiency for offline converter applications. They are ideally optimized for personal computer and CRT power supplies, but can be used in any number of offline applications where energy efficiency is critical. Coupled with the fact that the LX155x series requires a minimal set of external components, the series offers an excellent value for cost-conscious consumer applications.
Optimizing energy efficiency, the LX155x series demonstrates a significant power reduction as compared with other similar offline controllers. Table 1 compares the SG384x, UC384xA, and the LX155x start-up resistor power dissipation. The LX155x offers an overall 4X reduction in power dissipation.
Additionally, the precise oscillator discharge current gives the power supply designer considerable flexibility in optimizing system duty cycle consistency.
The current mode architecture demonstrates improved load regulation, pulse-by-pulse current limiting, and inherent protection of the power supply output switch. The LX155x includes a bandgap reference trimmed to 1%, an error amplifier, a current sense comparator internally clamped to 1V, a high current totem pole output stage for fast switching of power MOSFETs, and an externally programmable oscillator to set operating frequency and maximum duty cycle.
The undervoltage lock-out circuitry is designed to operate with as little as 250µA of supply current, permitting very efficient bootstrap designs.

Features
Ultra-Low Start-up Current (150µA Typical)
Trimmed Oscillator Discharge Current (2% Typical)
Initial Oscillator Frequency Better Than 14%
Output Pulldown During UVLO
Precision 2.5V Reference ( 2% maximum)
Current Sense Delay to Output (150ns Typical)
Automatic Feed Forward Compensation
Pulse-by-Pulse Current Limiting
Enhanced Load Response Characteristics
Under Voltage Lockout with Hysteresis
Double Pulse Suppression
High Current Totem Pole Output (±1A Peak)
500KHz Operation

Applications
Economy Off-Line Flyback or Forward Converters
DC-DC Buck or Boost Converters
Low Cost DC Motor Control