ADCHS LPC4370 Problems creation interface.

[fabiodebernardi]

good morning,
We are undertaking a project with the micro lpc4370 and we find it difficult to properly size the interface circuit for the analog readings by adchs.

We use the internal vref to 0.5V, in the datasheet is reported that the range of values are compared -+400mV to  vref. But in the datasheet lpc3470 page. 131

Symbol Parameter Conditions Min Typ Max Unit

VDC DC input common mode level          0.1          0.5          0.9 V
                                                               -2048            0          +2047 digit

We (range) input voltage peak-to-peak   0.72         0.8          0.88 V

The minimum value in this case may range from 0.1 to 0.14V?

The maximum value in this case can range from 0.86 to 0.94V?

We can not correctly interpret these data.

Can you help?

Thanks and good job

[Hui_Ma]

Hi

Please check my comments with your submit another thread(with same question):

https://community.nxp.com/thread/445056

Wish it helps.

Have a great day,
Ma Hui
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[haksookim1]

I'm using ADCHS from LPC4370.
I have a question because the ADC port is damaged during long-term use.

Circuit/Situation Description
  1. Used as Vin neg pin output.
  2. I checked the data sheet. ( 3.3V Max)
  3. Noise is generated in ADCHS(1~3) as mux operation waveform

In the datasheet, the ADC input voltage limit is set to 3.3V and is being used.
The circuit I am using is
  ADCHS0 ( max Input voltage  3.3V) 
  ADCHS1 ( max Input voltage  1.2V)
  ADCHS2 ( max Input voltage  1.2V)
  ADCHS3 ( max Input voltage  1.2V)
and the problem seems to occur when ADCHS1~3 periodically generate noise and ADCHS0 inputs at 3.3V level.

I am asking a question based on the above.
  1. What is the maximum input voltage when using ADCHS (12bit ADC)?
  2. If there is no problem with the input voltage, how can the phenomenon that the Mux operation waveform interferes be eliminated?

[okcn]

you mean :  it should be      0.1                    0.5                0.9 V

 but now it is                        0.1~0.14                             0.86~0.94

and the signal you send  is      0.72            0.8                0.88

What is the freq of your signal?     I guess, Maybe  4370 's   ADC   only can measure  high freq signal.

And maybe  you should measure your signal  with   Link-2- Labtool    first,  and compare that  with your data.