PCF85063ATLSLASH1 datasheet(17/55 Pages) NXP

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NXP Semiconductors

PCF85063A

Tiny Real-Time Clock/calendar with alarm function and I2C-bus

Measure the frequency on pin CLKOUT:

fmeas

Convert to time:

tmeas = 1 / fmeas

Calculate the difference to the ideal

period of 1 / 32768.00:

Dmeas = 1 / 32768 - tmeas

Calculate the ppm deviation compared

to the measured value:

Eppm = 1000000 × Dmeas / tmeas

Calculate the offset register value:

Mode = 0 (low power):

Offset value = Eppm / 4.34

Mode = 1 (fast correction)

Offset value = Eppm / 4.069

aaa-004375

sample calculation:

32768.48 Hz

30.517131 µs

0.000447 µs

14.648 ppm

3.375

3 correction pulses

are needed

3.600

4 correction pulses

are needed

Figure 11. Offset calibration calculation workflow

-6

-4

-2

aaa-004371

(3)

(2)

(1)

measured/calculated

deviation 14.648 ppm

deviation after

correction in

MODE = 0

+1.628 ppm

deviation after

correction in

MODE = 1

-1.628 ppm

With the offset calibration an accuracy of ±2 ppm (0.5 × offset per LSB) can be reached (see Table 12).

±1 ppm corresponds to a time deviation of 0.0864 seconds per day.

1. 3 correction pulses in MODE = 0 correspond to -13.02 ppm.

2. 4 correction pulses in MODE = 1 correspond to -16.276 ppm.

3. Reachable accuracy zone.

Figure 12. Result of offset calibration

PCF85063A

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Product data sheet

Rev. 7.1 — 8 November 2023

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