M41T82 datasheet(32/58 Pages) STMICROELECTRONICS

32 / 58 page

Clock operation

M41T82 M41T83

32/58

The on-chip capacitance can be calculated as follows:

For example:

●

CLOAD (12h = x0000000) = 12.5 pF,

●

CLOAD (12h =11001000) = 3.5 pF, and

●

CLOAD (12h = 00100111) = 17.4 pF.

The oscillator sees a minimum of 3.5 pF with no programmable load capacitance selected.

Note:

These are typical values, and the total load capacitance seen by the crystal will include

approximately 1-2 pF of package and board capacitance in addition to the Analog

Calibration register value.

Any invalid value of Analog Calibration will result in the default capacitance of 25 pF.

The combination of analog and digital trimming can give up to –93 to +156 ppm of the total

adjustment.

Figure 18 on page 33 represents a typical curve of clock ppm adjustment versus the Analog

Calibration value. This curve may vary with different crystals, so it is good practice to

evaluate the crystal to be used with an M41T8x device before establishing the adjustment

values for the application in question.

LOAD

--- AC6 AC0 value

–

decimal

() 0.25pF

[] 25pF

M41T82 Datasheet(PDF) 32 Page - STMicroelectronics