Thanks for all the replies guys. I realise I was not very detailed in my post, preferring to pose the question in general terms. The actual circuit I have is as follows. 1 L298 H-bridge driving a stepper motor. The driver is controlled by an L297 stepper motor controller. This generates the phase sequence & PWM for the driver. The 'Ground' end of the H-bridge is connected to ground through a current sense resistor. The net connecting the H-bridge to the current sense resistor is the 3mm wide one. The motor current passes through this net and the sense resistor to ground, hence the need for a wide trace. The purpose for the sense resistor is to give current feedback to the PWM generator. Routing the wide traces back to the L297 for feedback is not really an option. The sense input on the generator is an opamp input. I don't know if it is bipolar or not. Given that only short distances (>6cm total for the line from sense resistor to the opamp input) are involved I can use a thinner trace (0.35mm). There is no separate ground sense line. This configuration has worked fine for me in the past.
When I route a board I usually setup the width constraint for each net, autoroute the board and then manually cleanup. In this case the auto router will route the net using the 3mm thickness throughout. If the part of the net which did not have to be so wide could have its width defined seperatly, then the autorouter would route differently and probably better. The virtual short thing sounds interesting & I can see how it works. I'm less sure how the from-to width rule works never having used it. Thanks for all the feedback. Joe * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * To post a message: mailto:[EMAIL PROTECTED] * * To leave this list visit: * http://www.techservinc.com/protelusers/leave.html * * Contact the list manager: * mailto:[EMAIL PROTECTED] * * Forum Guidelines Rules: * http://www.techservinc.com/protelusers/forumrules.html * * Browse or Search previous postings: * http://www.mail-archive.com/[EMAIL PROTECTED] * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
