International Rectifier introduced the IRU3138 synchronous PWM controller integrated circuit (IC). The new device is a feature-rich controller with adjustable switching frequency, a 0.8V fixed voltage reference, and 1.5% accurate voltage tracking capability. The IRU3138 gives the designer a versatile solution that simplifies design and cuts component count for power management applications in desktop motherboards, hard disk drives, graphics cards and DDR memory arrays.
The new IRU3138 has a 1.0A peak output drive capability and supports currents in the 3A to 20A range. The new IC can be used as a general-purpose synchronous buck controller for on-board DC-DC conversion for output voltages as low as 0.8V.
The IRU3138 has the ability to supply an external reference voltage, thereby making the controller suitable for high-efficiency DDR memory applications. DDR memory requires the termination voltage (VTT) to be one half the supply voltage (VDDQ) within 3%. The IRU3138 integrates an error amplifier into the PWM controller package to simplify the VTT circuit. In addition, the IRU3138 integrates a high-side and low-side driver, eliminating external drive circuitry. This makes it easy to scale the design to drive multiple banks of memory.
The IRU3138 provides current levels of up to 20A in a synchronous buck converter, using the IRF6620 and IRF6623 power MOSFETs in the DirectFETTM package.
The maximum input voltage for the IRU3138 on the Vc and Vcc pins is 25V. Compared to competitive solutions, this makes the IRU3138 suitable for a wide range of input voltages. The IRU3138 can be programmed to operate between 200kHz and 400kHz using an external resistor, simplifying the optimization of the design and layout to obtain the highest efficiency. The use of a voltage mode control loop simplifies external component selection. The new device features under-voltage lockout for both Vc and Vcc supplies, an externally programmable soft start function as well as an output under-voltage detection that latches the device off when an output short is detected.
