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The TL284xB and TL384xB family of control ics provide the functionality necessary to implement off-line or dc-to-dc fixed frequency current mode control solutions with a minimum number of external components. The circuit implemented internally includes an undervoltage lock (UVLO) and a precision reference for trimming accuracy at the error amplifier input. Other internal circuits include logic circuits that ensure latching operation, pulse-width modulation (PWM) comparators that also provide current-limiting control, and totem pole output stages that generate or absorb peak current.The output stage is lower in the off state and is suitable for driving n channel mosFETs.
Functional block diagram
The TL284xB and TL384xB series are compatible with the pins of the standard TL284x and TL384x with the following improvements. The starting current is specified as 0.5 mA(maximum), while the oscillator discharge current is cut to 8.3 mA(typical). In addition, the maximum saturation voltage of the output is 1.2V when dropping 10 mA (VCC = 5V) under undervoltage locking conditions. The main differences between these family members are the UVLO threshold and maximum duty cycle range.
The typical UVLO thresholds for TLx842B and TLx844B devices are 16 V(on) and 10 V(off), making them ideal for offline applications. Typical thresholds for TLx843B and TLx845B devices are 8.4 V(on) and 7.6 V(off). The TLx842B and TLx843B devices can operate to a duty cycle approaching 100%. The TLx844B and TLx845B achieve a duty cycle range of 0% to 50% by adding an internal switch trigger that empties the output every other clock cycle. The tl284xb family of devices features operating temperatures from -40°C to 85°C. tl384xb series devices feature operating temperatures from 0°C to 70°C