电流模式PWM控制器 CURRENT MODE PWM CONTROLLER
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 • 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 The SG1844/45 family of control ICs provides all the necessary features to implement off-line fixed frequency, current-mode 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 under-voltage 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. The output is low in the off state to provide direct interface to an N-channel device. Both operate up to a maximum duty cycle range of zero to <50% due to an internal toggle flip-flop which blanks the output off every other clock cycle. The SG1844/45 is specified for operation over the full military ambient temperature range of -55°C to 125°C. The SG2844/45 is specified for the industrial range of -25°C to 85°C, and the SG3844/45 is designed for the commercial range of 0°C to 70°C.