LPC1768 - DAC PIN issue

[Dhaya]

Hi,

      We are working on DAC (P0_26), while configuration we set the value of 31. As a 10bit DAC, 0.10 V is expected but as per the datasheet ±10mV tolerance is acceptable.

     In all our customized board, output of the PIN is 0.11 V but in one board we get as 0.05V it reduces halfly. Kindly resolve this issue and navigate us to get rid from this

[ZhangJennie]

Hi Dhaya 

I think you should test the same code on your custom board?

What't the percentage of this incorrect DAC conversion issue?

In order to identify the problem on board or chip side, please get a "correct" board and a "incorrect" board, do LPC1768 A/B swap. How is the result?

Thanks,

Jun Zhang 

[Dhaya]

Yes, We verified in 2 controller board. In one board it shows 0.05V and on another it shows 0.10V (expected volt). While change the new controller in problem board, it works well as expected value.

Now we trying to use that incorrect controller in another board.

Note : Conversion error % is app. 50%. But while configure value of 313, it reaches nearly 0.98 V instead of 1.00V

[ZhangJennie]

Hi Dhaya 

Yes, please test the problem part on more board if possiable. 

Besides, If you have more samples, it's better to know the failure parts rate.

Where did you purchase the chips? from NXP website or local distributor?

Thanks,

Jun Zhang

[Dhaya]

 Controller : LPC1768FBD100

     LOT & ID : AYM579000

                       SSD22290

Imported from : Widekey International Ltd

[ZhangJennie]

How is it if  use that incorrect controller in another board? we need to verify the probelm on part itself or PCB.

[Dhaya]

While change the defect controller part in other 2 PCB's, it react like same. (Output volt is 0.005 V instead of 0.10V)

[ZhangJennie]

it shows the problem is on chip itself.

I checked your vendor is not under the distributor list:

https://www.nxp.com/part/LPC1768FBD100#/

For NXP official distributor, you can apply to take failure analysis of the part.

[Dhaya]

Sorry for the mislead in information. We got the controller LPC1768 from Elektronika who are authorised distributor of NXP. Kindly help us, how to solve this issue or how we can analyse failure part

[ZhangJennie]

I suggest you test lpcopen dac demo code on your board to isolate the possibility of SW issue.

https://www.nxp.com/design/software/development-software/mcuxpresso-software-and-tools-/lpcopen-libr...

LPC1769 code also works on LPC1768

Please also post your DAC schematic. let me check.

I didn't find this company on nxp website distributor list. please let me know if I missed.

[ZhangJennie]

Hi

According to LPC176x datasheet DAC electrical characteristics, we need to connect load resistance at min 1K, and load capacitance about 200pf.

Please try this.

Thanks,

Jun Zhang

[Dhaya · Accepted solution]

Here the verification is done on 5 different controllers and output taken on DAC pin