M41T93 datasheet(26/56 Pages) STMICROELECTRONICS

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Clock operation

M41T93

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DocID12615 Rev 8

As shown in Figure 12, 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 3.16 on page 42).

Figure 11. Crystal accuracy across temperature

AI07888

–160

010

3040506070

Frequency (ppm)

Temperature

°C

–10

–20

–30

–40

–100

–120

–140

–40

–60

–80

–20

= –0.036 ppm/

°C

2 ± 0.006 ppm/°C2

ΔF

= Kx (T – T

O = 25°C ± 5°C

Table 5. 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

( 1pF)

AC1

(0.5 pF)

AC0

(0.25 pF)

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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