Additional considerations

AN2971

2/12

Doc ID 15627 Rev 1

1

Additional considerations

The turnover point is the temperature at which the crystal is at its highest frequency. This is

Figure 1, it was assumed the turnover point was 25°C. It will in fact range between 20 and

30°C for most 32 KHz crystals.

Figure 2.

Typical temperature curves for three different turnover points after

calibration to 0 ppm at 25°C

During factory calibration of the M41T83 and M41T93, the oscillator frequency is adjusted

until the device is very close to 0 PPM at 25°C. This has the effect of moving the

temperature curve up and down.

If the turnover point is at 20°C, after factory calibration, the device will be at 0 PPM at 25°C,

but will run at its fastest at 20°C. This is depicted by the orange curve.

Similarly, if the turnover point is at 30°C, after factory calibration, the device will be at 0 PPM

at 25°C, but will run at its fastest at 30°C. This is depicted by the blue curve.

Thus, the temperature turnover point moves up and down with calibration, but remains at the

same temperature.

Three turnover points (k=0.036, typical)

-35

-30

-25

-20

-15

-10

-5

0

5

0

1020304050

TEMP (°C)

30

25

20

AM04628v1