How to calculate the sample time of MPC5744P ADC

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How to calculate the sample time of MPC5744P ADC

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jackjiang
Contributor II

Dears,

Datasheet page 80 have a tab for ADC parameter:

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Reference Manual page 1060 have a sequence chart:

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I don't understand the meaning of Sample time and Conversion time, how to explain these?

Thanks.

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davidtosenovjan
NXP TechSupport
NXP TechSupport
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davidtosenovjan
NXP TechSupport
NXP TechSupport

Hi, it is quite well described in RM section 36.5.11 Conversion time

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In the following description there are examples for better understanding:

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Note that DS specifies conversion time and sample time individually (as mentioned in the note below the table) thus it is needed to sum both times to get total conversion time. In other words in this table conversion time means all phase excluding sample time.

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jackjiang
Contributor II

Hi David,

Thanks for your reply.

As your say, when ADC_CLK = 80MHz(per cycle equal to 12.5ns), sample resolution is 12-bit, Tsample MIN is 250ns, so MIN sample cycles is 20d, and Tconv MIN is 650ns(MIN covnv cycles is 52d), then get the following formula:

software/hardware triggered (NSTART):
Subsequent/continuous conversion: 20 + ((12 + 1) × 4) + 2 = 20 + 52 + 2 = 74 cycles of AD_clk 

Tacd = 74 * 12.5 = 925ns, Fadc = 1s/925ns = 1.08MSPS > 1MSPS , right?

捕获1.PNG

Besides,

Why is there no ADC_CLK = 40MHz(Or other frequency) parameter for Tsample and Tconv in Table 27? because note that DS specifies "the minium value of sample time is 8".

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davidtosenovjan
NXP TechSupport
NXP TechSupport

Please, see following thread:

https://community.nxp.com/thread/462819