International Rectifier (IR) introduced the IR3621M and IR3621F 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 includes a full suite of power management features, including pre-bias protection, sequencing capability, hiccup current limit protection and tight voltage reference accuracy demanded by today's systems.
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 12V input, 2.5V output, the converter achieves up to 86% efficiency at 15A full load and 400kHz 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 two-phase requirements.
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 5mm x 5mm MLPQ package for improved thermal performance. 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 non-isolated 0.8V to 3.3V output DC-DC POL converters with either dual output rails up to 15A each, or single output rails up to 30A.
The pre-bias feature included in the IR3621 prevents the discharge of any pre-existing output voltage during the start-up of the POL, eliminating negative voltage spikes on the output. A negative voltage spike during start-up in many cases can cause damage to expensive network processor units (NPUs) and application-specific ICs (ASICs), so when a pre-bias condition occurs, it is critical that the output voltage charges to its required regulation voltage without going through the initial discharge cycle during soft-start initiation.
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° out-of-phase operation with programmable switching frequency up to 500kHz, reducing input and output filtering requirements and results in lower component count.
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 under- and over-voltage protection ensure system level security during fault conditions.
| Part Number | Package | Vref | Vout(adj) | Vout accuracy | Fsw | Deadtime | Junction Temp |
| IR3621M | 32-pin MLPQ (5mm x 5mm) | 0.8V | 0.8V-3.3V | +/-1% @ Tj=25degC | 200kHz - 500kHz | 50ns typ 100ns max |
-40°C to 125°C |
| IR3621F | 28-pin TSSOP | 0.8V | 0.8V-3.3V | +/-1.35% @ Tj=25degC | 200kHz - 500kHz | 50ns typ 100ns max |
-40°C to 125°C |
Design Assistance
The IRDC3621 Design Kit featuring the IR3621M is available.
Availability and Pricing
The new dual synchronous buck controller and driver ICs are available immediately. Pricing in 10,000-unit quantity is US $1.45 each for the IR3621F or IR3621FTR, and US $1.50 each for the IR3621M and IR3621MTR. Prices are subject to change.
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).
