ISL68201 Buck Controller Renesas Electronics ISL68201 Buck Controller features proprietary R4™ Technology. The Single-Phase R4 Digital Hybrid PWM Controller with PMBus/SMBus/I2C and PFM features a wide input and output voltage range. Integrated LDOs provide controller bias voltage for single-supply operation. Renesas Electronics ISL68201 with R4 control scheme has extremely fast transient performance, accurately regulated frequency control, and all internal compensation.