LPC MicrocontrollersのトピックRe: Wierd DAC behaviour

Wierd DAC behaviour

lpcware — Wed, 15 Jun 2016 17:06:00 GMT

Content originally posted in LPCWare by Chandrika R on Tue Jan 05 07:29:58 MST 2016
Hi,

I am using the DAC peripheral in LPC1549 micro controller (100-pin controller) to generate the DAC output which in turn i am using it to generate 0-10V. I am observing a weird behavior in it. If I am loading the DAC count value equivalent to get 10V output, I am able to get the correct value at my output side and the expected DAC output value(DAC count value: 2641; DAC output value = 2.12V to get 10V overall output) is also correct. But when the same code which i had used in debug mode, if i just flash it and run it it is getting saturated i.e., I am not even able to go above 9.6V(DAC output voltage getting saturated at 2.09V itself). Has anyone found this kind of an issue? Please guide me with this as I am not able to figure it out.

Re: Wierd DAC behaviour

lpcware — Wed, 15 Jun 2016 17:06:01 GMT

Content originally posted in LPCWare by miccio on Thu Jan 07 04:01:06 MST 2016
hi! :)

do you experience the same behavior with the lpcopen example dac code? if not, it's hard to guess what could be wrong without some code..

Re: Wierd DAC behaviour

lpcware — Wed, 15 Jun 2016 17:06:01 GMT

Content originally posted in LPCWare by Chandrika R on Thu Jan 07 04:26:39 MST 2016
Yes i do observe the same behavior with the example code also.

Re: Wierd DAC behaviour

lpcware — Wed, 15 Jun 2016 17:06:02 GMT

Content originally posted in LPCWare by vtw.433e on Thu Jan 07 06:27:05 MST 2016
Sounds like a GND problem. If removing the debug probe affects the behavior, I would guess that the probe is supplying a stable GND, and your circuit is no.

Re: Wierd DAC behaviour

lpcware — Wed, 15 Jun 2016 17:06:03 GMT

Content originally posted in LPCWare by jeffreyeowen on Thu Jan 28 17:20:10 MST 2016
Did you ever resolve this problem? I have a similar problem where the DAC output on an LPC1857 clamps at about 1V as you ramp up the DAC value. Does this on multiple boards running the NXP DAC example project.

Re: Wierd DAC behaviour

lpcware — Wed, 15 Jun 2016 17:06:03 GMT

Content originally posted in LPCWare by jeffreyeowen on Fri Jan 29 06:21:40 MST 2016
One more bit of information I just noticed. I have grounded all the dedicated analog pins, including pin E3 (dedicated ADC0/DAC pin). Would grounding pin E3 prevent pin B1 (P4[4]) from getting all the way to 3.3V when configured to be a DAC output? I would just try it and see, but I can't un-ground pin E3 given the way the board is designed.

Re: Wierd DAC behaviour

lpcware — Wed, 15 Jun 2016 17:06:04 GMT

Content originally posted in LPCWare by jeffreyeowen on Fri Jan 29 12:49:32 MST 2016
Well, just verified that grounding pin E3 will make the DAC output on pin B1 never go above 1V on the Keil dev board. Anyone know of a workaround for this?