ADCHS LPC4370 Problems creation interface.

[fabiodebernardi]

good morning,

We are undertaking a project with the micro lpc3470 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

[fabiodebernardi]

Hi Hui,

Do you mean that we had to consider for single ended config. the range 0.1 to 0,9V without tolerance?

THKS!

Fabio

[Hui_Ma]

Hi Fabio,

It is based on customer application to determine which ADCHS mode will be used.

The range 0.1V to 0.9V single ended mode without tolerance (vin_pos should be in the range
from 0.50 ± 0.4 V ).

Wish it helps.

Have a great day,
Ma Hui
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[fabiodebernardi]

Hi Hui_Ma,

Thank you for the reply.

good job

[Hui_Ma]

Hi

LPC4370 12-bit high speed ADC common mode is using internal vin_neg 0.5V reference voltage connects with ADCHS_NEG pin. The vin_pos should be in the range from 0.50 ± 0.4 V.

Customer could find below data from LPC4370 datasheet:

When deselect the internal vin_neg and supply vin_neg externally at pin ADCHS_NEG by setting DCINNEG to 0. Then customer is using the ADC with differential mode.

So, customer need to refer below table about one of ADCHS_[0:5] input pin and ADCHS_NEG input voltage peak to peak range:

When ADC works in differential mode, the peak to peak typical value is 0.8V.

For example if the ADCHS_NEG input voltage is 0.7V, the ADCHS_0 pin input voltage could low to 0V and up to 1.2V (ADCHS module with Measurement range 0 to 1.2 V  feature).

The Vin(range) Min. value 0.72V and Max. value 0.88V are based on the test results. The typical value is 0.8V.

Wish it helps.

Have a great day,
Ma Hui
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Note: If this post answers your question, please click the Correct Answer button. Thank you!
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[fabiodebernardi]

Good morning,

This last consideration:

"The Vin(range) Min. value 0.72V and Max. value 0.88V are based on the test results. The typical value is 0.8V."

is it applicable to single ended ADC configuration?

[Hui_Ma]

Hi Fabio,

The Vin(range) is only suitable for differential mode , which doesn't applicable to single ended ADC configuration.

Thank you for the attention.

best regards,

Hui