| Features • Optimized for Off-Line and DC to DC Converters • Low Start-Up Current (≦0.5mA) • Automatic Feed Forward Compensation • Pulse-by-Pulse Current Limiting • Enhanced Load Response Characteristics • Under-Voltage Lockout (UVLO) with Hysteresis • Double Pulse Suppression • High Current Totem Pole Output • Internally Trimmed Bandgap Reference • Current Mode Operation to 500KHZ • Low Ro Error Amplifier General Description The AP3842/3/4/5 family of control ICs provides the necessary features to implement off-line or DC to DC fixed frequency current mode control schemes with a minimal external parts count. Internally implemented circuits include under voltage lockout featuring start-up current less than 0.5 mA, a precision reference trimmed for accuracy at the error amp input, logic to insure latched operation, a PWM comparator which also provides current limit control, and a totem pole output stage designed to source or sink high peak current. The output stage, suitable for driving N-Channel MOSFETs, is low in the off-state. Differences between members of this family are the under-voltage lockout thresholds and maximum duty cycle ranges. The AP3842 and AP3844 have UVLO thresholds of 16V(on) and 10V(off), ideally suited for off-line applications. The corresponding thresholds for the AP3843 and AP3845 are 8.5V and 7.6V. The AP3842 and AP3843 can operate to duty cycles approaching 100%. A range of the zero to < 50% is obtained by the AP3844 and AP3845 by the addition of an internal toggle flip flop which blanks the output off every other clock cycle. |
