XRP77XX: Extending the MOSFET Gate Drive Conductors

Focus:

In power supply applications with high switching frequencies, gate drivers are located close to the power MOSFETs they are driving to mitigate parasitic effects. Typically, designers limit this distance between gate drivers and MOSFETs to less than 6 inches. However, this can be inconvenient when a supply rail needs to be located far from a PWM controller with on-chip gate drivers. This application note describes a PCB layout technique that will allow more than 6 inches of separation between drivers and MOSFETs, while still maintain good performance. The technique treats the drive lines (traces) as a pulse transmission line with a capacitive termination representing the MOSFET's gate and Miller capacitances. To implement the transmission line, a dual stripline is applied, so that the resulting magnetic field produced by the gate driver's current pulse, which charges and discharges the MOSFET capacitance, is cancelled by the proximity effect of the opposing currents. Design guidelines and a design example based on Exar's XRP77XX digital multi-channel PWM controllers are presented. Experimental results for a POL converter using this dual stripline technique are compared against a design using DrMOS, which integrates gate drivers and MOSFET and so represents optimum performance.

What you’ll learn:

• How to separate gate drivers and power MOSFETs in POL applications without sacrificing high-speed performance

Notes:

Exar Application Note ANP-35.

View the Source

Author & Publication:

Kevin Parmenter and Trevor Latham, Vendor website, May 02 2011

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