AN2971

Example

Doc ID 15627 Rev 1

7/12

Figure 5.

32 KHz crystal curve, PPM versus temperature

–160

010

20

3040506070

Frequency drift (ppm)

Temperature °C

80

–10

–20

–30

–40

–100

–120

–140

–40

–60

–80

20

0

–20

= –0.036 ppm/°C

k

∆f = k x (T – T

2

f

T

Factory calibration value, FCAL, places operation at ~0 PPM at 25°C.

Step 1: Read temperature

Step 2: Look up ΔPPM from PPM vs.

temperature graph/table (figure 5 and

figure 6)

Example:

Temperature read is 58°C.

ΔPPM

Curve/table shows that clock

will be ~43 PPM slow. Thus, ΔPPM

should be +43 PPM (Here, + means

faster).

Fast

Slow

43 PPM

Steps

Analog calibration sequence:

AM03097v1