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Controller simplifies DC/DC conversion circuitry

An International Rectifier product story

Edited by the Electronicstalk editorial team Jul 27, 2004

A new synchronous PWM controller integrated circuit offers adjustable switching frequency, a 0.8V fixed voltage reference and 1.5% accurate voltage tracking capability.

A new synchronous PWM controller integrated circuit (IC) from International Rectifier (IR) is a feature-rich device 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.

IR's new device has a 1.0A peak output drive capability and supports currents in the 3 to 20A range.

The IC can be used as a general-purpose synchronous buck controller for onboard DC/DC conversion for output voltages as low as 0.8V.

An ability to supply an external reference voltage makes the IRU3138 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%.

By integrating an error amplifier into the PWM controller package, the IRU3138 simplifies 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 convertor, using IR's IRF6620 and IRF6623 power MOSFETs in the company's DirectFET package.

Maximum input voltage for the IRU3138 on the Vc and Vcc pins is 25V.

Compared with competing solutions, this makes the IRU3138 suitable for a wide range of input voltages.

The IRU3138 can be programmed to operate between 200 and 400kHz using an external resistor, simplifying the optimisation of the design and layout to obtain the highest efficiency.

Use of a voltage mode control loop simplifies external component selection.

The new device features undervoltage lockout for both Vc and Vcc supplies, an externally programmable soft start function, as well as an output undervoltage detection that latches the device off when an output short is detected.

A reference design kit (IRDC3138) is available for the IRU3138.