National, SiLabs partnership delivers dc/dc converter reference design

Santa Clara, Calif. — National Semiconductor Corp. and Silicon Laboratories Inc. (Austin, Tex.) have unveiled a new quarter-brick isolated dc/dc converter evaluation board and reference design to help power-supply designers get higher power density in networking, communications and high-end server applications.

The isolated dc/dc converter evaluation board, featuring National’s LM5035C pulse-width modulation (PWM) controller and Silicon Labs’ Si8420 ISOpro digital isolator, provides power-supply designers with a highly efficient 100-W reference design in a quarter-brick form factor. The evaluation board reduces the time required for product characterization and design adaptation to the customer’s specific requirements, said National.


The reference design demonstrates a viable 36-V to 75-V input half-bridge converter for power module or embedded power applications. The design survives input transients up to 100 V as commonly required in communications equipment and protects the power distribution system with hiccup-mode fault protection.

National said the LM5035C half-bridge PWM controller delivers power density and performance advantages for small-form-factor isolated dc/dc converter modules, and has been optimized for use with digital isolators to provide further power density improvements.

The LM5035C PWM controller includes integrated 2-A half-bridge gate drivers and SyncFET outputs that control the secondary-side synchronous rectifier MOSFETs through the Si8420 digital isolator. Dead time between the main and synchronous rectifier on/off transitions is adjustable with a single external resistor.

Silicon Labs’ ISOpro family of digital isolators uses digital RF technology to communicate data across an isolation barrier. Using the Silicon Labs Si8420 digital isolator in place of pulse transformers eliminates numerous design issues such as duty cycle limitations and non-monotonic decay of output during shutdown, said the company. In addition, use of digital isolators improves efficiency and saves board space by eliminating the need for pulse transformers.

Availability: The quarter-brick reference design is available now at no charge for download from
Pricing: The evaluation board is priced at $135. To purchase the evaluation board, visit
Resources: LM035C demo video.