Cherry Adds New PWM ControllersMarch 16, 1999 by Jeff Shepard
Cherry Semiconductor Corp. (East Greenwich, RI) introduced four new pulse width modulation (PWM) controllers at this week's Applied Power Electronics Conference in Dallas. The CS-51221 and CS-51227 are designed for feed forward operation in sub 150W dc/dc power converters, while the CS-5124 and CS-5126 are intended for sub-50W dc/dc converters.The CS-51221/51227 controllers feature all of the features necessary for basic voltage-mode operation. The CS-51221 designed for applications that require a full set of control and protection features, while the CS-51227 is a basic device targeted at more cost sensitive applications. The 16-lead CS-51221 provides programmable pulse-by-pulse overcurrent protection, overvoltage protection with programmable hysteresis, undervoltage lockout, accurate programmable duty cycle limit, current sense blanking and bi-directional synchronization. It also includes a soft-start feature, and its synchronization output can be used to synchronize the device to other power supplies.The 8-lead CS-51227 offers undervoltage lockout, leading-edge current sense blanking and 50ns shutdown propagation delay. Both controllers are fixed frequency, 1MHz devices that drive an external power MOSFET switch with up to 1A of sink/source gate drive current. Both feature thermal shutdown, start up current of 75uA, up to 20V supply operation, and typical start/stop voltage thresholds of 4.6V and 3.7V. The CS-51221 is priced at $1.54, and the CS-51227 is priced at $1.45, in quantities of 10,000.According to Cherry, a typical converter design based on its CS-5124/5126 controllers will require up to 40 percent less board space and eliminate as many as 14 external components. The controllers integrate a number of control and protection features into an 8-lead plastic SO narrow package. The CS-5124 has a voltage bias pin that can be used to control a series pass transistor for operation over a wide input voltage range without an external pre-regulator. The CS-5126 has a clock synchronization pin that allows it to be synchronized to signals ranging from 30 percent slower than its internal oscillator frequency (200kHz) up to 1MHz. Features include remote on/off control, undervoltage lockout, thermal shutdown, soft start timing, pulse-by-pulse overcurrent protection, leading-edge current blanking and a direct optocoupler interface. Both controllers operate over a supply voltage range of 7.7V to 20V. In quantities of 10,000, the CS-5124 is priced at $1.61 each, and the CS-5126 is priced at $1.65 each.