FPGA Power circuitry

Earlier this week I finished the schematic for the FPGA power circuit using the LTC3607 dual buck regulator rather than the pair of TPS62170s as had been my plan. This evening I finished up the test board for this circuit and sent it off to OSH Park for fabrication. I expect to get it back before the first weekend in May.

Here's an image of the PCB, measuring 2" wide by 1.5" high:

Why these particular dimensions? The area of the PCB behind the VFD is about 6.7" wide by 1.5" high (170mm x 38mm). In that space needs to go all the power circuitry:

• The AC rectifier and filter
• The +3.3V and +1.2V buck regulators
• The +30V boost regulator
• The VFD filament driver and transformer
• The printer drivers and position sensors

Sounds like a challenge, eh? Well, maybe not. As laid out above, the AC rectifier and filter (D1 and C9) and the +3.3V and +1.2V buck regulators occupy an area of about 1.5" wide by 1.0" high. The rather loosely laid-out board I sent off Monday contains the +30V boost and VFD filament circuitry in an area about 1.5" wide by 1.25" high. Thus all the circuitry on both of these boards will fit easily height-wise, and leave a space 3.7" wide. I doubt the printer driver and sensor circuits will occupy as wide as 1".

The front side of the rest of the board is taken up with contact patterns for the keypad and switches, so the VFD drivers and the FPGA will have to go on the back side of the keypad. The FPGA only projects 0.062" (1.6mm) from the surface of the board so there's plenty of room for it behind the top couple rows of keys. The tricky part will be to juggle the location of the vias so that none of them end up intruding into a keypad contact area.

My plan was to get this board sent off a week after the previous one so I'd be able to work on that one while this one was being fabbed. I just got notice that OSH Park has slipped it into one of their "Super Speed" batches (gratis) so both may show up at the same time.

My goal now is to place the order for the parts for both boards with DigiKey on Monday. And probably Mouser. I can't buy it all from one or the other: DigiKey doesn't stock the Halo transformer for the filament driver, and Mouser won't have stock of the LT3494 boost regulator until July. Bummer.