Cherry Offers CS51221 and CS51227 PWM ControllersMarch 25, 1999 by Jeff Shepard
Cherry Semiconductor Corp. (East Greenwich, RI) introduced the CS51221 and CS51227, two new voltage-mode pulse-width modulated PWM control ICs designed for feed forward operation in sub 150W dc/dc power converters. Both controllers have all features necessary for basic voltage-mode operation. Designed for applications requiring a full set of control and protection features, the 16-lead CS51221 provides programmable pulse-by-pulse over-current protection, over-voltage protection with programmable hysteresis, under-voltage lockout, accurate programmable duty cycle limit, leading edge current sense blanking, and bi-directional synchronization. A soft start feature allows controlled start up of the output voltage and protection against voltage overshoots. The SYNC output can be used to synchronize the device to other power supplies.Though it offers fewer options, the 8-lead CS-51227 still contains many of the control capabilities required for supply operation, including undervoltage lockout, leading edge current sense blanking and 50ns shutdown propagation delay. The fixed frequency, 1MHz devices drive an external power MOSFET switch with up to 1A of sink/source gate drive current. Both have a thermal shutdown feature and fast gate drive output rise and fall times (25ns into a 1nF load). The devices feature start up current of 75mA, up to 20V supply operation, and typical start/stop voltage thresholds of 4.6V and 3.7V, respectively. Available in a plastic 16-lead SO narrow or plastic 16-lead standard dual-in-line package, the CS51221 is priced at $1.54 each in 10,000-piece quantities. The CS51227 comes in an 8-lead plastic SO narrow dual-in-line package, and is priced at $1.45 each in 10,000-piece quantities.