Cherry Adds New PWM Controllers

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.