AN2971

Example

Doc ID 15627 Rev 1

9/12

Figure 7.

Typical oscillator accuracy versus load capacitance

Step 3:

Example (continued):

Analog calibration value read was

0x14 (+5 pF).

Move +43 PPM from 5 pF (0x14).

DECREASING LOAD CAP.

-20.0

0.0

20.0

40.0

60.0

80.0

100.0

-18.0 -15.0

5.0

9.75

Analog Calibration

Value, AC,

register 0x12

OFFSET TO

NET EQUIV. LOAD

10.0

3.5

5.0

12.5

15

17.4

0xC8 0xBC

0xA9

0x00

0x14

0x27

INCREASING LOAD CAP.

SLOWER

FASTER

DECREASING LOAD CAP.

-20.0

0.0

20.0

40.0

60.0

80.0

100.0

-18.0 -15.0

Analog Calibration

Value, AC,

register 0x12

OFFSET TO

NET EQUIV. LOAD

INCREASING LOAD CAP.

SLOWER

FASTER

Read factory calibration value:

Set OTP bit to 1, wait 4ms, then

read analog calibration register

(address 0x12). This will return

factory calibration value (for 0

PPM @ 25°C).

Step 4: Find factory calibration value on

the curve, then move ΔPPM (from

step 2) up/down from there and

read new calibration value from

PPM vs.load capacitance

table/graph (figure 7 and figure 8)

+43PPM

New calibration value

Value read is –10.25 pF (0xA9).

Step 5: Clear OTP bit, then write new

value to analog calibration

register.

Clear OTP bit at address 0x13.

Write 0xA9 to address 0x12.

Steps (continued)

0x94

–10.25

7.38

–5.0

0.0

AM03099v1