Data Sheet

SD2405ALPI IIC 串行接口的实时时钟IC

3) Here, the clock accuracy at room temperature varies along with the variation of the

characteristic of crystal oscillator.

4) The influence of stray capacitance on circuit board

These factors will cause large errors

Using the time trimming circuit gain or lose of clock may be adjusted with high

precision by changing clock pulses for one second every 20 seconds.

F6 to F0:

The time trimming circuit adjust one second count based on this register readings

when second digit is 00，20，or 40 seconds. Normally, counting up to seconds

is made once per 32,768 of clock pulse (or 32,000 when 32.000KHz crystal is

used) generated by the oscillator. Setting data to this register activates the time

trimming circuit.

set to “0”.

F6 is set to “1”.

Counts will not change when (F6, F5, F4, F3, F2, F1, F0) are set to (*, 0, 0, 0, 0, 0, *).

For example, when 32.768KHz crystal is used.

When (F6, F5, F4, F3, F2, F1, F0) are set to (0,1, 0, 1, 0, 0, 1), counts will change

as:

32768+（29-1）*2=32824

(clock will be delayed) when second digit is 00,

20, or 40.

When (F6, F5, F4, F3, F2, F1, F0) are set to (0, 0, 0, 0, 0, 0, 1), counts will remain

32,768 without changing when second digit is 00, 20, or 40.

When (F6, F5, F4, F3, F2, F1, F0) are set to (1, 1, 1, 1, 1, 1, 0), counts will

change as: 32768-（1+1）*2=32764 (clock will be advanced) when second

digit is 00, 20, or 40.

Adding 2 clock pulses every 20 seconds:

2/（32768*20）=3.051ppm

(or 3.125ppm

when 32.000KHZcrystal is used), delays the clock by approx. 3ppm.

Likewise, decrementing 2 clock pulses advances the clock by 3ppm. Thus

the clock may be adjusted to the precision of±1.5ppm.

Note: that the time trimming function only adjusts clock timing and oscillation

frequency but 32.768KHz clock output is not adjusted

Computational method of time trimming register value

1. When oscillation frequency

> target frequency

（clock gain）