参数资料
型号: MC34708VM
厂商: Freescale Semiconductor
文件页数: 31/159页
文件大小: 0K
描述: IC POWER MANAGEMENT 206MAPBGA
标准包装: 160
应用: 通用
电源电压: 1.8 V ~ 4.5 V
工作温度: -40°C ~ 85°C
安装类型: 表面贴装
封装/外壳: 206-LFBGA
供应商设备封装: 206-MAPBGA(13x13)
包装: 托盘
Functional Block Description
RTC Timer Calibration
A clock calibration system is provided to adjust the 32.768 cycle counter that generates the 1.0 Hz timer for RTC timing registers.
The general implementation relies on the system processor to measure the 32.768 kHz crystal oscillator against a higher
frequency and more accurate system clock such as a TCXO. If the RTC timer needs a correction, a 5-bit 2’s complement
calibration word can be sent via the SPI to compensate the RTC for inaccuracy in its reference oscillator.
Table 17. RTC Calibration Settings
Code in RTCCAL[4:0]
Correction in Counts per 32768 Relative correction in ppm
01111
00011
00001
00000
11111
11101
10001
10000
+15
+3
+1
0
-1
-3
-15
-16
+458
+92
+31
0
-31
-92
-458
-488
The available correction range should be sufficient to ensure drift accuracy in compliance with standards for DRM time keeping.
Note that the 32.768 kHz oscillator is not affected by RTCCAL settings; calibration is only applied to the RTC time base counter.
Therefore, the frequency at the clock output CLK32K is not affected.
The RTC system calibration is enabled by programming the RTCCALMODE[1:0] for desired behavior by operational mode.
Table 18. RTC Calibration Enabling
RTCCALMODE
00
01
10
11
Function
RTC Calibration disabled (default)
RTC Calibration enabled in all modes except coin cell only
Reserved for future use. Do not use.
RTC Calibration enabled in all modes
The RTC Calibration circuitry can be automatically disabled when main battery contact is lost or if it is so deeply discharged that
the RTC power draw is switched to the coin cell (configured with RTCCALMODE=01).
Because of the low RTC consumption, RTC accuracy can be maintained through long periods of the application being shut down,
even after the main battery has discharged. However, the calibration can only be as good as the RTCCAL data provided, so
occasional refreshing is recommended to ensure any drift influencing environmental factors have not skewed the clock beyond
desired tolerances.
MC34708
Analog Integrated Circuit Device Data ?
31
Freescale Semiconductor
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