Bulk capacitance on high-current PCB rails safely controlled with 30V MOSFET

October 07, 2015 // By Graham Prophet
Enabling rapid and safe discharge of bulk capacitors on FPGA power rails, the DMN3027LFG 30V N-channel MOSFET has been designed as a switch that can handle those specific loads.

The latest FPGAs found in telecoms equipment, servers and data centers have multiple power rails that need to be correctly sequenced to safely power these systems up and down. Designers of high-reliability DC-DC power supplies can achieve this using this MOSFET.

The DMN3027LFG has an R DS(on) of 26 mΩ at 4.5V, which is low enough to discharge a 15 mF capacitor in under 10msec but not so low that sharply rising current peaks could cause EMI issues or give rise to transient thermal stresses, potentially damaging the MOSFET or capacitor bank. Under the typical FPGA low-voltage rail conditions of 1V, this current is self-limited by the MOSFET channel resistance as specified in the safe operating area (SOA). This SOA is given at a +60°C ambient temperature with minimal heat-sinking to support the typical application conditions, allowing peak currents up to 20A to be safely handled in under 10msec.

The DMN3027LFG comes in a PowerDI3333 package, which has a low thermal resistance from junction to exposed pad of under 10°C/W enabling the dissipation of up to 3W. It is priced at $0.25 (10,000).

Diodes Inc.; www.diodes.com