Qtouch PTC Slider Project.

[amitchell]

Hey, I am working on a Qtouch PTC Project that controls an LED boost driver. Though I would share what I have so far and see what improvements can be made.

I am using an Atmega328PB for the Qtouch PTC and PWM output to the Boost driver TPS61165. I have 6mm of Z height to work this little puppy into, so sourcing some components has been a hassle.

Input protection is LTC4365 Overvoltage, Undervoltage and Reverse Supply Protection Controller. This seems like a nice little unit. 12vdc normal input with an 11-13vdc allowable input controlled by the LTC4365.

On the original boards I was seeing some 1.2MHz switching frequency noise in my MCU circuit, I decided to try out some 1uF feed through caps to soften that up on this go around.

I think i am looking at about 45dB insertion loss per FTC at 1.2MHz. https://product.tdk.com/info/en/catalog/datasheets/eemc_3tf_yff-hc.pdf
(this is the 1206 footprint also have an 0805)

I am trying two LDO's (LP2985A) to smooth out the power further, One at each end of the 1mm pitch FFC cable. Previous board had one.

On the boost board I was thinking it may be smart to isolate the ground at the Boost circuit all the way back to the GND input. Do you think it is wise to do this? I have already kept a single point ground under the boost controller. I am also unsure of the top pour, is this worth it? I am keeping a 25mil isolation on everything.

On the MCU slider board I debated with myself about the 16MHz crystal isolation, I did remove a guard ring that I had in place. It seams alot of datasheets are contradictory in terms of crystal isolation/guarding.

Any glaring errors or issues that I am missing?

[DTJ]

Just out of interest - what sort of SIL header are you using for the programming connector? It looks like alternate pins are offset a little.


How are you mounting the boards - I don't see mounting holes.

[amitchell]

Just out of interest - what sort of SIL header are you using for the programming connector? It looks like alternate pins are offset a little.


How are you mounting the boards - I don't see mounting holes.

Good eyes.

That is a "lock" footprint from the sparkfun eagle library actually. Offset is 5mils so a standard SIL header is held in place and not flopping around.

I am using adhesive to attach the slider to the panel. I think I will clamp the Boost board in place using the outside edges. I cannot use screws through the z-axis. The panel is 8mm thick and I get to use 6mm of this for the boards.

[DTJ]

Just out of interest - what sort of SIL header are you using for the programming connector? It looks like alternate pins are offset a little.

That is a "lock" footprint from the sparkfun eagle library actually. Offset is 5mils so a standard SIL header is held in place and not flopping around.

That's a good idea. It craps me off doing the odd hand assembly job and having to hold them in place and vertical and getting a hot finger as the pins warm up.