ST10F276E datasheet(196/235 Pages) STMICROELECTRONICS

196 / 235 page

Electrical characteristics

ST10F276E

196/235

Doc ID 12303 Rev 3

Supposing to design the filter with the pole exactly at the maximum frequency of the

signal, the time constant of the filter is:

Using the relation between CF and CS and taking some margin (4000 instead of 2048),

it is possible to define CF:

As a consequence of Step 1 and 2, RC can be chosen:

Considering the current injection limitation and supposing that the source can go up to

12V, the total series resistance can be defined as:

from which is now simple to define the value of RL:

Now, the three elements of the external circuit RF, CF and RL are defined. Some conditions

discussed in the previous paragraphs have been used to size the component; the others

must now be verified. The relation which allows to minimize the accuracy error introduced by

the switched capacitance equivalent resistance is in this case:

So the error due to the voltage partitioning between the real resistive path and CS is less

then half a count (considering the worst case when VA = 5V):

The other conditions to verify are if the time constants of the transients are really and

significantly shorter than the sampling period duration TS:

For a complete set of parameters characterizing the ST10F276E A/D converter equivalent

circuit, refer to Table 93: A/D converter characteristics on page 187.

πf

------------

15.9

μs

4000C

⋅

16nF

πf

--------------------

995

Ω 1kΩ

≅

INJ

-------------

INJ

-------------

2.9k

–

---------------

10M

-------------------------------------------------------------------------

2.35mV

⋅

--- LSB

()

2.8ns

⋅

<< TS = 1μs

⋅

10R

⋅

() 290ns

⋅

< TS = 1μs

ST10F276E Datasheet(PDF) 196 Page - STMicroelectronics

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