m41t93 STMicroelectronics, m41t93 Datasheet - Page 19

• Manufacturer Part Number: m41t93
• Description: Serial Spi Bus Rtc With Battery Switchover
• Manufacturer: STMicroelectronics

3.3
Real time clock accuracy
The M41T93 is driven by a quartz controlled oscillator with a nominal frequency of
32,768Hz. The accuracy of the Real Time Clock is dependent upon the accuracy of the
crystal, and the match between the capacitive load of the oscillator circuit and the capacitive
load for which the crystal was trimmed. Temperature also affects the crystal frequency,
causing additional error (see
The M41T93 provides the option of clock correction through either manufacturing calibration
or in-application calibration. The total possible compensation is typically –93 ppm to +156
ppm. The two compensation circuits that are available are:
1.
2.
Figure 9.
An Analog Calibration register (12h) can be used to adjust internal (on-chip) load
capacitors for oscillator capacitance trimming. The individual load capacitors C
C
0.25pF. This translates to a calculated compensation of approximately ±30 ppm (see
Analog calibration (programmable load capacitance) on page
A Digital Calibration register (08h) can also be used to adjust the clock counter by
adding or subtracting a pulse at the 512Hz divider stage. This approach provides
periodic compensation of approximately –63 ppm to +126 ppm (see
(periodic counter correction) on page
XO
(see
Internal load capacitance adjustment
Figure
9), are selectable from a range of –18pF to +9.75pF in steps of
Figure 10 on page
XI
XO
C XO
C XI
20).
Crystal Oscillator
23).
22).
Digital calibration
AI11804
XI
and
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