BCT 384X Family

Current Mode Controller

General Description

The BCT3842 family of control ICs provide pin-for-pin replacement of the industry standard UC3842 series of devices. The devices are redesigned to provide significantly improved tolerances in power supply manufacturing. The 2.5 V reference has been trimmed to 1.0% tolerance. The oscillator discharge current is trimmed to provide guaranteed duty cycle clamping rather than specified discharged current. The circuit is more completely specified to guarantee all parameters impacting power supply manufacturing tolerances.

In addition, the oscillator and flip-flop sections have been enhanced to provide additional performance. The RT/CT pin now doubles as a synchronization input that can be easily driven from open collector/open drain logic inputs. This sync input is a high impedance input and can easily be used for externally clocked systems. The new flip-flop topology allows the duty cycle on the BCT3844/5 to be guaranteed between 49 and 50%. The BCT3843/5 requires less than 0.5mA of start-up current over the full temperature range.  

Features

• 2.5V bandgap reference trimmed to 1.0% and temperature-compensated
• Standard temperature range extended from -40 to 1050C
• BCT3842/3 oscillations trimmed for precision duty cycle clamp
• BCT3844/5 have exact 50% max duty cycle clamp

• Advanced oscillator design simplifies synchronization
• Improved specs on UVLO and hysteresis provide more predictable start-up and shutdown
• Improved 5 V regulator provides better AC noise immunity
• Guaranteed performance with current sense pulled below ground

Pin Configurations – Top view