Dual-output PWM IC Drives Synchronous Buck DC-DC Converters

Sep 21, 2005 11:49 AM

The IR3621M and IR3621F from International Rectifier are voltage-mode, dual-output bi-phase synchronous buck controller-driver ICs for high performance point-of-load (POL) buck converters used in networking, computing and communications systems. The IR3621 features pre-bias protection, sequencing capability, hiccup current limit protection and tight voltage reference accuracy. The IRDC3621 Design Kit, featuring the new IR3621M, demonstrates the complete dc-dc converter performance, while showcasing its full range of power management features. For a 12-V input and 2.5-V output, the converter achieves up to 86% efficiency at the 15-A full load, and 400 kHz switching frequency when the IR3621M is used with two optimized HEXFET MOSFETs, such as the IRF7821 and IRF8113. Typical applications include powering dual logic application-specific ICs (ASICs), DDR memory power management, or other multi-rail or 2-phase requirements.

The IR3621M provides ±1% output voltage accuracy, and the IR3621F provides ±1.35% output voltage accuracy. Both provide pre-bias protection and are ideal for nonisolated 0.8-V to 3.3-V output dc-dc POL converters with either dual-output rails up to 15 A each, or single output rails up to 30 A. The pre-bias feature included in the IR3621 prevents the discharge of any pre-existing output voltage during the startup of the POL, eliminating negative voltage spikes on the output. For single-output bi-phase configurations, the IR3621 uses the output inductor dc resistance as a current sharing reference, eliminating external shunt resistors. The IR3621 features 180 degrees out-of-phase operation with programmable switching frequency from 200 kHz to 500 kHz, reducing input and output filtering requirements and the external component count. The typical deadtime value is 50 ns; the maximum value is 100 ns.

Two independently programmable soft-start functions allow system-level sequencing of output voltages in various configurations, critical for system level start-up protocols. The IR3621 includes a “power good” output signal, which can be used to trigger a sequential rise of output voltages across multiple POL converters. Protection features such as selectable hiccup or latched current limit, thermal shutdown, and undervoltage and overvoltage protection ensure system-level security during fault conditions.

The IR3621 is offered in two package styles: The IR3621F is housed in a 28-lead TSSOP package and the IR3621M is housed in a 32-pin 5-mm × 5-mm MLPQ package for improved thermal performance. Pricing in 10,000-unit quantity is $1.45 each for the IR3621F or IR3621FTR, and $1.50 each for the IR3621M and IR3621MTR. A lead-free version of the IR3621M (32-pin MLPQ) will be available in Q4 CY 2005, as part number IR3621MPbF. The device will be compliant with the Restriction of Hazardous Substances Directive (RoHS).

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