applying power to VS but not VCC or VCC but not VS

[lusher00]

I am working with a board in the lab that is essentially the same setup as the TMC428 eval board. The only major difference is that the microcontroller is on a separate board. The board with the microcontroller has a 6pin connector on it that includes a chip select, +9V, GND and all the necessary SPI stuff. The 9V is regulated down to 5V on the board with the motor drivers. I have a separate 24V connector on the motor drivers for the VS connector. Now in the end product one switch will control power to both VCC and VS but in the setup I have now, at times i have used two separate power supplies to power VS and VCC. They share a common ground but they dont always get turned on at the same time. What kinds of things can happen if i tried to communicate with the TMC428 and command the motors to turn when power is not actually applied to VS and then i turn VS on after the configurations such as v_min, v_max etc have been sent? What if I applied VS without powering VCC? I have blown up several MOSFETS, TMC239's and and sense resistors. This is the only difference i see between my setup and the setup on the eval board.

[lusher00]

well i changed my setup so that VCC is regulated to 5V from the supply that powers VS so that one is never on without the other and it blew again after a while. Its like the source of the P-channel mosfet is shorted to the source of the N-channel mosfet on the FDS8960 half h-bridge. I end up with a short from VS to the high side of the sense resistor and the driver starts to smoke. This happens when the motor is not even connected. Sorry if I am not so good a describing this. I really need more support here or I will have to scrap the Trinamic solution and try some parts from a different company.

[lusher00]

Could using the same pull down resistors for BL1 and BL2 on three different driver chips cause a problem?

[TRINAMIC_BD]

Powering on VCC and VS seperately is allowed and is not any problem. The resistors for low current signals are uncritical, as long as the GND connection is stable. Most probably, you have a layout problem - please see here:
http://www.trinamic.com/ttdg/viewtopic.php?t=959
Do you use a two layer layout? Have you gone through the checklist?
If you want, you can post a link to your layout, or email to tmcinfo at trinamic dot com for comments from our side.