bkgable wrote:I wonder what the thermal resistance would be for a 1x2x1/8 " piece of copper soldered to the power tab? Maybe it could be conductively isolated from a board layer. Are you thinking two layer board?
Keep in mind that this is an HTSSOP28, not a PowerSO. Unfortunately, there isn't a PowerSO version of the L6470 as of yet
I'm looking at a two-layer board, as four-layer is rather cost-prohibitive (and internal layers can't sink much heat at all anyways). They recommend 12 thermal vias underneath the chip (I'd imagine they mean under the thermal pad). I'm attempting to create as much surface area on the module as possible for heat sinking via PCB to make the heatsink's job easier.
In regards to the second option, I've removed the limit switch resistor and filter cap (to be included on the motherboard instead) and the ADC voltage divider circuit (ditto) to reduce the part count.
Regarding the move of the limit switch resistor and filter from the module to a motherboard, not everyone is going to want or have limit switches, and they would need to be tied high. No sense adding extra parts that are never going to be used, and could easily be added to the motherboard if desired.
Regarding the move of the Power Compenation Voltage Divider to the motherboard, A) This allows the ADC to be used either as an ADC or as Power Compensation (as decided by the user and/or motherboard setup), and B) the Voltage Divider potentiometer needed is much too large to add to each module, and the voltage that the divider outputs would be the same for all modules on the same motherboard. This helps, again, reduce the part count and overall cost, and allows more room for cooling.
aldenhart wrote:You might consider doubling up on the motor outs 1A, 1B, 2A, 2B, and certainly doubling (at least) the motor power and grounds.
Here's a slightly updated version. The connectors I'm looking at (Digikey# S9206-ND for the module, and one of S9198-ND (through hole) or S9190-ND (surface-mount) for the motherboard), and as such, pins are rated at 3A each. I guess I could always make it 2x14 and add another couple grounds if needed.
I'm thinking that the signal pins will likely take a route around the outside of the bottom layer of the PCB and pop up through vias to reach their respective pins, while power and output will stay on the top layer whenever possible (of course, all this allowing for the largest uninterrupted ground pours possible for heatsinking)