
RS5C372A/B
38
2.4 Time Trimming Circuit
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. When adjustment with this circuit is not necessary, set (F
6
, F
5
, F
4
, F
3
, F
2
, F
1
, F0)
to (
*
, 0, 0, 0, 0, 0,
*
) to disable adjustment. (
*
mark indicates 0 or 1.)
Adjustment amount may be calculated using the following formula.
2.4-1 When oscillation frequency*
1
>target frequency*
2
(clock gains)
Adjustment amount*
3
= (Oscillation frequency – Target frequency + 0.1)
Oscillation frequency
×
3.051
×
10
–6
= (Oscillation frequency – Target frequency)
×
10 + 1
When 32.000kHz crystal oscillator is used, the same formula,
Adjustment amount
= (Oscillation frequency – Target frequency + 0.1)
Oscillation frequency
×
3.125
×
10
–6
= (Oscillation frequency – Target frequency)
×
10 + 1
is used.
*
1) Oscillation frequency : Clock frequency output from the INTRB (32KOUT for the RS5C372B) pin as in “2.2 Oscillation Frequency Measurement” at a
room temperature.
*
2) Target frequency
Since temperature characteristics of a 32.768kHz crystal oscillator are such that it will generally generates the highest fre-
quency at a room temperature, we recommend to set the target frequency to approx. 32768.00Hz to 32768.10Hz (+3.05ppm
to 32768Hz).
We also recommend setting of approx. 32000.00Hz to 32000.10Hz (3.125ppm to 32000Hz) also for the 32.000kHz crystal.
Note that this value may differ based on the environment or place where the device will be used.
*
3) Adjustment amount
: A frequency to be adjusted to.
: A value to be set finally to F
6
to F
0
bits. This value is expressed in 7bit binary digits with sign bit (two's compliment).
2.4-2 When oscillation frequency=target frequency (no clock gain or loss)
Set the adjustment value to 0 or +1, or –64 or –63 to disable adjustment.
2.4-3 When oscillation frequency<target frequency (clock loses)
Adjustment amount = (Oscillation frequency – Target frequency)
Oscillation frequency
×
3.051
×
10
–6
= (Oscillation frequency – Target frequency)
×
10
Also a 32.000kHz crystal is used, the same formula,
Adjustment amount =(Oscillation frequency – Target frequency)
Oscillation frequency
×
3.051
×
10
–6
= (Oscillation frequency – Target frequency)
×
10
is used.
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