Electronic Design

"Think Different" About PS Topologies With Ultra-Low On-Resistance MOSFETs

The CoolMOS CS—eight years in the making. Back in 1997, Infineon (then Siemens) introduced a technology for manufacturing power MOSFETs with 190-mΩ conduction losses in TO220 packaging. Then in 2000, the company improved the process and cut on-resistance (RDS(ON)) down to 190 mΩ while increasing switching speeds.

To reduce on-state resistance, CoolMOS implements a compensation structure in the MOSFET's vertical drift region. Essentially, Infineon drives the source and drain more deeply into the die than conventional process technologies allow, shrinking the chip area needed to carry the same current. The latest process enhancement, designated CoolMOS CS, is characterized by devices with 99-mΩ RDS(ON) in a TO220 package, 150-V/ns switching speed, still with a 600-V blocking capability.

At March's Applied Power Electronics Conference in Austin, CoolMOS co-inventor Gerald Deboy challenged designers to change their thinking about power-supply (PS) topologies and MOSFETs with very low switching losses. For example, he first showed a 1000-W reference design for a server supply based on the usual phase-shift zero-voltage-switching (ZVS) topology.

It was incrementally more efficient at full power when using the new MOSFETs. Then, observing that server supplies are generally used in a redundant configuration and that ZVS-supply efficiencies under light loads are typically in the mid-70% range, he showed an equivalent reference design based on an Interleaved Two Transistor Forward (ITTF) topology.

Generally, this topology isn't considered efficient enough for supplies larger than around 600 W. While it was slightly less efficient with the CoolMOS CS switches than the ZVS reference design at full load, it was a full 7% percent more efficient at one-third of full load.

The first products in the 600-V CoolMOS CS Server series are sampling now. The IPW60R045CS has a guaranteed-maximum 45-mΩ RDS(ON) (continuous Idmax at 100° C = 38 A) and a typical 150-nC gate charge in a TO247 package. The IPP60R099CS and IPW60R-099CS come with a 99-mΩ RDS(ON) (19-A continuous Id) and a typical 150-nC gate charge in a TO220 or TO247 package, respectively. Volume production will start next month.

Unit price for a IPP60R099CS device in a TO220 will be less than 4.00 Euro for orders in excess of 10,000.


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