DESCRIPTION
The SG1844/45 family of control ICs provides all the necessary features to implement off-line fixed frequency, currentmode switching power supplies with a minimum number of external components. Current-mode architecture demonstrates improved line regulation, improved load regulation, pulse-by pulse current limiting and inherent protection of the power supply output switch. The bandgap reference is trimmed to ±1% over temperature. Oscillator discharge current is trimmed to less than ±10%. The SG1844/45 has undervoltage lockout, current-limiting circuitry and start-up current of less than 1mA. The totem-pole output is optimized to drive the gate of a power MOSFET.

KEY FEATURES
■ OPTIMIZED FOR OFF-LINE CONTROL
■ LOW START-UP CURRENT (<1mA)
■ AUTOMATIC FEED FORWARD COMPENSATION
■ TRIMMED OSCILLATOR DISCHARGE CURRENT
■ PULSE-BY-PULSE CURRENT LIMITING
■ ENHANCED LOAD RESPONSE
■ CHARACTERISTICS
■ UNDER-VOLTAGE LOCKOUT WITH 6V HYSTERESIS (SG1844 only)
■ DOUBLE PULSE SUPPRESSION
■ HIGH-CURRENT TOTEM-POLE OUTPUT
■ INTERNALLY TRIMMED BANDGAP REFERENCE
■ 500kHz OPERATION
■ UNDERVOLTAGE LOCKOUT SG1844 - 16 volts SG1845 - 8.4 volts
■ LOW SHOOT-THROUGH CURRENT <75mA OVER TEMPERATURE