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FM31T376-G 参数 Datasheet PDF下载

FM31T376-G图片预览
型号: FM31T376-G
PDF下载: 下载PDF文件 查看货源
内容描述: 系统监控器和温度补偿实时时钟( TCXO )与内嵌晶体 [System Supervisor & Temperature Compensated RTC(TCXO) with Embedded Crystal]
分类和应用: 晶体电源电路电源管理电路石英晶振温度补偿晶振光电二极管监控时钟
文件页数/大小: 26 页 / 796 K
品牌: RAMTRON [ RAMTRON INTERNATIONAL CORPORATION ]
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FM31T372/374/376/378-G  
32.768 kHz Clock Output  
Note: Systems using lithium batteries should clear the  
VBC bit to 0to prevent battery charging. The VBAK  
circuitry includes an internal 1 Kseries resistor as  
a safety element.  
The 32.768 kHz clock (with precision equal to that of  
the built-in crystal oscillator) can be output via the  
FOUT pin. This output is not temperature  
compensated. This clock can be disabled by clearing  
the FOEN bit to „0‟.  
32.768kHz  
512 Hz  
1 Hz  
/OSCEN  
Oscillator  
W
32.768 kHz  
crystal  
Clock  
Divider  
Update  
Logic  
Date  
6 bits  
Years  
8 bits  
Months  
5 bits  
CF  
Hours  
6 bits  
Minutes  
7 bits  
Seconds  
7 bits  
Days  
3 bits  
R
User Interface Registers  
Figure 8. Real-Time Clock Core Block Diagram  
timekeeping error. The 512Hz calibration output  
must be measured at +25°C. This output is not  
temperature compensated. The user converts the  
measured error in ppm and writes the appropriate  
correction value to the calibration register. The  
correction factors are listed in the following tables.  
Positive ppm errors require a negative adjustment  
that removes pulses. Negative ppm errors require a  
positive correction that adds pulses. Positive ppm  
adjustments have the CALS (sign) bit set to 1,  
whereas negative ppm adjustments have CALS = 0.  
Offset/Aging Compensation  
The user can expect the RTC to be accurate from the  
factory. The RTC is calibrated at the factory at room  
temperature. The CAL bits setting in Register 01h  
will likely be a non-zero value. This is the initial  
calibration value assigned at the factory prior to  
shipment. The device may need re-calibrating after  
solder reflow or after some period of time due to  
crystal aging.  
If the user needs to re-calibrate the RTC, the  
following describes the steps to change the  
calibration setting. Before making changes to the  
CAL bits, the user can read these bits to verify the  
current setting is an expected value. To enter  
calibration mode, the CAL bit in a register 00h must  
be set to 1. When the RTC is in calibration mode,  
the CAL/PFO output pin is dedicated to the  
calibration function and the power fail output is  
temporarily unavailable. Calibration operates by  
applying a digital correction to the counter based on  
the frequency error. In this mode, the CAL/PFO pin  
is driven with a 512 Hz (nominal) square wave. Any  
measured deviation from 512 Hz translates into a  
The calibration setting is stored in F-RAM so is not  
lost should the backup source fail. It is accessed with  
bits CAL.5-0 in register 01h. This value only can be  
written when the CAL bit is set to „1. To exit the  
calibration mode, the user must clear the CAL bit to a  
0. When the CAL bit is 0, the CAL/PFO pin will  
revert to the power fail output function.  
Note: Temperature compensation is disabled when  
the CAL bit is set to ‘1’. The user should clear this bit  
to allow temperature compensation to activate.  
Rev. 1.1  
Apr. 2011  
Page 8 of 26  
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