0
\$\begingroup\$

I have designed boards that were using the CH340G USB-UART converter based on the below schematic. And they worked just fine, and back in the day I also paid zero attention to things like differential pairing/impedance matching etc. I even used the auto router to route everything back then.

enter image description here

Now I am about to lose my mind, I have the below layout. And the thing is that when I connect this to the computer, it does nothing or gets recognized but the computer tells me that the device doesn't work properly. In any case it doesn't work.

enter image description here

I have tested the same chip on another board to see if it is busted. But it works perfectly fine on a board I designed previously. The only thing that are different are the smaller smd Crystal and I have accidentally routed the differential pair on 0,2mm width. It should have been 0,4mm.

The upper copper pour is ground, below is 3,3V.

To see what is worng I have tried:

1)I replaced the crystal and soldered a larger THT crystal on the smd pads. Did not work.

2)I cut out the D+ and D- traces, and replaced them with twisted wires. That also did not work.

I am failing to see my own error. I would appreciate any input.

\$\endgroup\$
9
  • 1
    \$\begingroup\$ I don't actually see continuity between the ground pours. Maybe it's there, but it's not visible in the slice you have provided. In any case the crystal load cap grounds should go back pretty directly to the chip Vss pin. \$\endgroup\$ May 26, 2021 at 21:54
  • \$\begingroup\$ @SpehroPefhany I updated the slice. It is connected through the bottom. \$\endgroup\$
    – Emre Mutlu
    May 26, 2021 at 21:58
  • \$\begingroup\$ @SpehroPefhany the worse thing is that the same circuit works on a breadboard. \$\endgroup\$
    – Emre Mutlu
    May 26, 2021 at 22:06
  • \$\begingroup\$ What is RST and RTS and IDD? And where are your voltage readings? \$\endgroup\$ May 26, 2021 at 22:56
  • 1
    \$\begingroup\$ my guess: check the datasheet of the crystal, and recalculate the load capacitors c10/c11. \$\endgroup\$ May 27, 2021 at 0:43

1 Answer 1

0
\$\begingroup\$

After Chengxian Zhangs comment I have increased the 10pF capcitors to 20pF. And the problem was solved. It seems that it was a far simpler problem than I originally anticipated.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.