I have finished my LPC1343 basic development board,just based on specs from datasheet and some referred from microbuilders.eu. I'm unsure if the board design is good or not so I've attached my schematics. Some things I'm concerned about are:

    1.Power supply
    2.D+ and D- from usb through 33 ohm resistor to chip and additional usb softconnect if necessary
    3.Testing LED.
    4.Separate switches for RESET and USB ftoggle.
    5.12MHz crystal oscillator with 16 pF caps.

My question: Is the board design is good enough to work or will it go wrong? If something is wrong, what is wrong with it?

overall image of sch The reset and usbtoggle switch connections The USB section,oscillator and power supply]3 [Tester LED and other pins]4

  • \$\begingroup\$ Which power supply are you using? \$\endgroup\$
    – Funkyguy
    Dec 7, 2015 at 20:36

1 Answer 1


There are a few things that I'd point out:

1) As you noted in the below comments, you are using a diode to buck the voltage from a 3.7V battery. I've recommended against that since, as they are used, batteries lose their voltage level so your VCC line will vary depending on how much charge is in the battery. I'd recommend a real power supply over a diode since you'll remove that varied voltage as well as having a real regulated line. You'll need something with a low dropout voltage or brownout detection since your voltage difference between the battery and your required VCC voltage isn't that large.

2) Your USB resistors are fine. Just remember that when you lay your PCB out, that USB uses differential signaling. This means that they need to be length-matched and routed accordingly.

3) LED looks fine

4) Your USB_Ftoggle button isn't necessary. USB_Ftoggle signal is an output. USB_Ftoggle signal description

5) Your crystals capacitors. You have 16pF in place and I'm curious where you got those values. The LPC1343 development board uses 18pF for its 12MHz crystal, which is also recommended in the LPC1343 datasheet in Table 21 on page 61.

One other thing is I'm curious why you have a test point on the D+ signal of your USB but not the D- signal. You can't really use that for anything.

  • \$\begingroup\$ Actually for the power supply,I planned to take it from a Li-ion mobile phone battery(3.7V max.).I schematics ,you'll note that I used a diode(assume Vf=0.7).At that point,I will get almost near to 3.0V supply,which I assume that it's sufficient to run controller \$\endgroup\$
    – Aadarsh
    Dec 8, 2015 at 8:48
  • \$\begingroup\$ 1.In that schematics,I used a diode(assume Vf=0.7V) and the power source which I planned to use is a Li-ion mobile phone battery(3.7V max.).So at that point I will get about 3.0V(from datasheet I noted limiting value from 2V to 3.6V. 2.capacitors is my mistake,what you told is right which I noticed now. 3.I kept my D+ and D- signal as close as possible to microcontroller and also with thick signal lines ,without bends. \$\endgroup\$
    – Aadarsh
    Dec 8, 2015 at 9:06
  • \$\begingroup\$ from application note AN10986,I saw a line describing(page no 3) "Holding PIO0_1 low during power-up will trigger the on-chip ISP firmware to enter ISP mode (unless it is disabled by the NO_ISP code read protection [CRP] mode). Once ISP mode has been entered, the USB VBUS line PIO0_3 is checked. If high, then USB ISP will be entered." .So I used a button at usb-f toggle. you told that test point at D+,which is actually for USB softconnect.I am not confident on that part.So I just kept it as test point(assuming that its not so necessary) \$\endgroup\$
    – Aadarsh
    Dec 8, 2015 at 9:10
  • 1
    \$\begingroup\$ @Aadarsh I'm not sure how much current you plan on pulling through the diode, but they do have a max current limit and are not meant for in-series voltage regulation. You could use a AP7331 or if you need a through-hole part MIC29152WT \$\endgroup\$
    – Funkyguy
    Dec 8, 2015 at 15:05
  • 1
    \$\begingroup\$ @Aadarsh I think you should be fine, just make sure you route the traces directly from the USB to the MCU differentially. As for the soft-connect, I'm worried about your LED. That circuit is essentially giving the D+ line a current path to ground...which it will most likely take. I'd recommend removing the LED, resistor, and the connection to ground. For the soft-connect, you aren't supposed to have the source of the FET connected to ground. I'm referencing the LPC1343 users manual and blog.ilektronx.com/2011/09/… \$\endgroup\$
    – Funkyguy
    Dec 8, 2015 at 15:22

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