Analog Devices Inc./Maxim Integrated

The LT1246/LT1247 are 8-pin, fixed frequency, current mode, pulse width modulators. These devices are designed to be improved plug compatible versions of the industry standard UC1842 PWM circuit. The LT1246/LT1247 are optimized for off-line and DC/DC converter applications. They contain a temperature compensated reference, high gain error amplifier, current sensing comparator, and a high current totem pole output stage ideally suited to driving power MOSFETs. Start-up current has been reduced to less than 250µA. Cross-conduction current spikes in the totem pole output stage have been eliminated, making 1MHz operation practical. Several new features have been incorporated. Leading edge blanking has been added to the current sense comparator. This minimizes or eliminates the filter that is normally required. Eliminating this filter allows the current sense loop to operate with minimum delays. Trims have been added to the oscillator circuit for both frequency and sink current, and both of these parameters are tightly specified. The output stage is clamped to a maximum VOUTof 18V in the on state. The output and the reference output are actively pulled low during under-voltage lockout.ApplicationsOff-Line ConvertersDC/DC Converters

The LT1248 provides active power factor correction for universal off-line power systems. By using fixed high frequency PWM current averaging, without the need for slope compensation, the LT1248 achieves far lower line current distortion with a smaller magnetic element than systems that use either peak-current detection or zero current switching approaches in both continuous and discontinuous modes of operation.The LT1248 uses a multiplier containing a square gain function from the voltage amplifier to reduce the AC gain at light output load and thus maintains low line current distortion and high system stability. The LT1248 also provides filtering capability to reject line switching noise which can cause instability when fed into the multiplier. Line current dead zone is minimized with low bias voltage at the current input to the multiplier.The LT1248 provides many protection features including peak current limiting and overvoltage protection, and can be operated at frequencies as high as 300kHz.ApplicationsUniversal Power Factor Corrected Power SuppliesPreregulators Up To 1500W

The LT1252 is a low cost current feedback amplifier for video applications. The LT1252 is ideal for driving low impedance loads such as cables and filters. The wide bandwidth and high slew rate of this amplifier make driving RGB signals between PCs and workstations easy. The linearity of the LT1252 is outstanding; it is unsurpassed for driving composite video.The LT1252 is available in the 8-pin DIP and the S8 surface mount package. For higher performance and shutdown operation, see the LT1227. For dual and quad amplifiers with similar performance see the LT1253/LT1254.ApplicationsRGB Cable DriversComposite Video Cable DriversGain Blocks in IF Stages