The 3842/43/44/45 are fixed frequency current mode PWM controller. They are specially designed for OFF−Line and DC to DC converter applications with a minimal external components. Internally implemented circuits include a trimmed oscillator for precise duty cycle control, a temperature compensated reference, high gain error amplifier, current sensing comparator, and a high current totempole output ideally suited for driving a power MOSFET. Protection circuitry includes built undervoltage lockout and current limiting. The 3842 and 3844 have UVLO thresholds of 16 V (on) and 10 V (off). The corresponding thresholds for the 3843/ 45 are 8.4V (on) and 7.6V (off). The 3842) and 3843 can operate within 100% duty cycle. The 3844 and 3845 can operate within 50% duty cycle. The 384X has Start-Up Current 0.17mA (typ).

The 3842/43/44/45 are fixed frequency current mode PWM controller. They are specially designed for OFF−Line and DC to DC converter applications with a minimal external components. Internally implemented circuits include a trimmed oscillator for precise duty cycle control, a temperature compensated reference, high gain error amplifier, current sensing comparator, and a high current totempole output ideally suited for driving a power MOSFET. Protection circuitry includes built undervoltage lockout and current limiting. The 3842 and 3844 have UVLO thresholds of 16 V (on) and 10 V (off). The corresponding thresholds for the 3843/ 45 are 8.4V (on) and 7.6V (off). The 3842) and 3843 can operate within 100% duty cycle. The 3844 and 3845 can operate within 50% duty cycle. The 384X has Start-Up Current 0.17mA (typ).

The accuracy of the chip +5.1V reference  voltage is 1%. Because the reference voltage is within  the input common- mode range of the error  amplifier, there is no need for an external resistor.  3525 can work in master- slave mode and can also  be synchronized with external clock. The dead time  can be adjusted by the resistance between CT and  discharge terminal. Other functional circuits inside  the chip also include: soft start circuit, turn- off circuit  and under- voltage circuit.  The output stage of the control chip is  a high- power totem- pole output, and its source  current and sink current exceed 150mA, which gives  a logic level of "NOR" and a low level when it is in  the "off" state trait.