M41T82 datasheet(32/64 Pages) STMICROELECTRONICS

32 / 64 page

Clock operation

M41T82, M41T83

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DocID012578 Rev 19

As shown in Figure 19, the relationship between oscillator speed and load capacitance is

not linear. When operating on the left end of the curve, small changes in load capacitance

have more effect than when operating on the right end of the curve. For example, at –15 pF,

a 3 pF reduction to –18 pF should result in the part running about 30 ppm faster (from

+65 ppm to +95 ppm). Conversely, at +5 pF, adding 3 pF to get to +8 pF should only slow

the part by about 4 ppm (from –8 ppm to –12 ppm).

3.4.3

Pre-programmed calibration value

Users of the M41T83 in the embedded crystal package have the option of using the factory

programmed analog calibration value (refer to Section 3.17 on page 49).

Figure 18. Crystal accuracy across temperature

AI07888

–160

Frequency (ppm)

Temperature

°C

–10

–20

–30

–40

–100

–120

–140

–40

–60

–80

–20

= –0.036 ppm/

°C2 ± 0.006 ppm/°C2

∆F = Kx (T–T

O = 25°C ± 5°C

Table 7. Analog calibration values

Addr

Analog

calibration

value

CXI, CXO

CLOAD

(1)

ACS

(±)

AC6

(16 pF)

AC5

(8 pF)

AC4

(4 pF)

AC3

(2 pF)

AC2

(1 pF)

AC1

(0.5 pF)

AC0

(0.25 pF)

½(CXI, CXO)

12h

0 pF

25 pF

12.5 pF

3 pF

28 pF

14 pF

5 pF

30 pF

15 pF

–7 pF

18 pF

9 pF

9.75 pF(2)

34.75 pF

17.4 pF

–18 pF(3)

7 pF

3.5 pF

1. CLOAD = 1/(1/CXI + 1/CXO).

2. Maximum negative calibration value.

3. Maximum positive calibration value.

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