LPC MicrocontrollersのトピックCustom LPC4337 PCB Feedback

Custom LPC4337 PCB Feedback

lpcware — Wed, 15 Jun 2016 18:59:47 GMT

Content originally posted in LPCWare by avr458 on Sun Mar 10 02:22:42 MST 2013
While I have been testing and debugging my first revision of my LPC4337 PCB I prepared a new design. I believe I have corrected all the design problems I had with the first one but before I send it out to be fabbed I want to make sure that I have done everything correctly and considered everything. I have attached a smart PDF exported from Altium that include my schematic and PCB (layers and composite). I want feedback on the specifics of the LPC4337 as well as feedback on my routing job/overall design.

Re: Custom LPC4337 PCB Feedback

lpcware — Wed, 15 Jun 2016 18:59:47 GMT

Content originally posted in LPCWare by wmues on Sun Mar 10 13:10:27 MST 2013
1) I am missing a Pulldown Resistor (1MOhm) at USB Device VBUS.

2) Several 1117 Voltage Regulators are instable with low ESR capacitors (ceramic) for output. Use another regulator which is specified for ceramic capacitor to avoid problems.

Re: Custom LPC4337 PCB Feedback

lpcware — Wed, 15 Jun 2016 18:59:48 GMT

Content originally posted in LPCWare by avr458 on Mon Mar 11 00:58:39 MST 2013
So I can't use that 3.3 v-reg with a ceramic cap? Which one should I use? I need 1-1.5 amps of 3.3v (its got to be able to power Arduino shields + the board).
Also why would I need a pulldown on V-bus? V-bus is just the power from the USB port, only D- and D+ are for coms and thus require pulldowns.

Re: Custom LPC4337 PCB Feedback

lpcware — Wed, 15 Jun 2016 18:59:49 GMT

Content originally posted in LPCWare by wmues on Mon Mar 11 03:17:02 MST 2013
I would use the 1117 with an output current of 500mA or less. If you need more output current, the 1117 will get too hot. For 1.5A, you will need a DC DC converter. Try TI TPS62063 or equivalent.

If you have no Pulldown on VBUS, this pin will be floating and your software might be fooled to detect that the device is plugged over USB.

Re: Custom LPC4337 PCB Feedback

lpcware — Wed, 15 Jun 2016 18:59:50 GMT

Content originally posted in LPCWare by suckfish on Tue Mar 12 11:48:55 MST 2013
It looks like you've routed the USB ID and VBUS lines very close to D+/D-. Probably better to keep D+/D- away from other things as far as possible. [Even better, swap the JTAG header and USB socket - that would keep the high speed USB traces much shorter.]

Re: Custom LPC4337 PCB Feedback

lpcware — Wed, 15 Jun 2016 18:59:50 GMT

Content originally posted in LPCWare by wlamers on Wed Mar 27 07:46:51 MST 2013
Probably a little bit late to respond, but the VBus pin already has an internal pull-down resistor. See datasheet:

--- USB0_VBUS - I/O VBUS pin (power on USB cable). This pin includes an internal pull-down resistor of 64 k (typical)  16 k.

I am not sure if you use the USB as a host. If you only use it as a device you can (or need?) to omit the 15k pull-down's also. Since these are for the host side only. The switchable 1.5k pull-up resisotrs (internal in the uC) are used to negotiate the bus speed, overruling the 15k pull-down's on the host side. See manual:

--- USB0_DP I/O USB0 bidirectional D+ line. The D+ line has an internal 1.5 k pull-up. This pull-up is enabled when software sets the RS bit (Bit 0) in the USBCMD register and the USB0 controller sees a valid VBUS voltage