M48T128V-70PM1 STMICROELECTRONICS [STMicroelectronics], M48T128V-70PM1 Datasheet - Page 13

• Manufacturer Part Number: M48T128V-70PM1
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

M48T128Y, M48T128V
One method is available for ascertaining how much calibration a given M48T128Y/V may
require. This involves setting the clock, letting it run for a month and comparing it to a known
accurate reference and recording deviation over a fixed period of time.
Calibration values, including the number of seconds lost or gained in a given period, can be
found in the STMicroelectronics application note, “TIMEKEEPER calibration.”
This allows the designer to give the end user the ability to calibrate the clock as the
environment requires, even if the final product is packaged in a non-user serviceable
enclosure. The designer could provide a simple utility that accesses the calibration byte. For
example, a deviation of 21 seconds slow over a period of 30 days would indicate a –8 ppm
oscillator frequency error, requiring a +2(WR100010) to be loaded into the calibration byte
for correction.
Figure 7.
Figure 8.
NORMAL
POSITIVE
CALIBRATION
NEGATIVE
CALIBRATION
-100
-20
-40
-60
-80
ppm
20
0
Crystal accuracy across temperature
Clock calibration
0
5
ΔF = -0.038
10
F
15
Doc ID 5746 Rev 6
T
20
0
ppm
= 25 °C
C
2
25
(T - T
30
0
)
2
± 10%
35
40
45
50
55
60
65
Clock operations
70
°C
AI00594B
AI02124
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