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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  
The serial number is located in registers 11h to 18h.  
The lock bit is SNL, register 0Bh bit 7. Setting the  
SNL bit to 1disables writes to the serial number  
registers, and the SNL bit cannot be cleared.  
Real-Time Clock (TCXO) Operation  
The real-time clock is a timekeeping function that  
can be battery or capacitor backed for continuous  
operation. The RTC is operated by a temperature  
compensated crystal oscillator (TCXO) based on an  
embedded 32.768 kHz crystal.  
The RTC consists of an oscillator, clock divider, and  
a register system for user access. It divides down the  
32.768 kHz time-base and provides a minimum  
resolution of seconds (1Hz). Static registers provide  
the user with read/write access to the time values. It  
includes registers for seconds, minutes, hours,  
day-of-the-week, date, months, and years. A block  
diagram (Figure 8) illustrates the RTC function.  
Figure 8. IBAK vs. VBAK Voltage  
The minimum VBAK voltage varies linearly with  
temperature. The user can expect the minimum VBAK  
voltage to be 1.23V at +85°C and 1.90V at -40°C.  
The tested limit is 1.55V at +25°C. The minimum  
VBAK voltage has been characterized at -40°C and  
+85°C but is not 100% tested.  
The user registers are synchronized with the  
timekeeper core using R and W bits in register 00h  
described below. Changing the R bit from 0to 1‟  
transfers timekeeping information from the core into  
holding registers that can be read by the user. If a  
timekeeper update is pending when R is set, then the  
core will be updated prior to loading the user  
registers. The registers are frozen and will not be  
updated again until the R bit is cleared to 0. R is  
used for reading the time.  
Setting the W bit to 1locks the user registers.  
Clearing it to 0causes the values in the user  
registers to be loaded into the timekeeper core. W is  
used for writing new time values. Users should be  
certain not to load invalid values, such as FFh, to the  
timekeeping registers. Updates to the timekeeping  
core occur continuously except when locked.  
Figure 9. VBAK (min.) vs. Temperature  
Trickle Charger  
To facilitate capacitor backup, the VBAK pin can  
optionally provide a trickle charge current. When the  
VBC bit, register 0Bh bit 2, is set to 1the VBAK pin  
will source approximately 80µA until VBAK reaches  
VDD or 3.75V whichever is less. In 3V systems, this  
charges the capacitor to VDD without an external  
diode and resistor charger. There is a Fast Charge  
mode which is enabled by the FC bit (register 0Bh,  
bit 5). In this mode the trickle charger current is set to  
approximately 1 mA, allowing a large backup  
capacitor to charge more quickly.  
Backup Power  
The real-time clock/calendar is intended to be  
permanently powered. When the primary system  
power fails, the voltage on the VDD pin will drop.  
When VDD is less 2.4V the RTC (and event counters)  
will switch to the backup power supply on VBAK. The  
clock operates at extremely low current in order to  
maximize battery or capacitor life. However, an  
advantage of combining a clock function with  
F-RAM memory is that data is not lost regardless of  
the backup power source.  
In the case where no battery is used, the VBAK pin  
should be tied to VDD  
.
The IBAK current varies with temperature and voltage  
(see DC parametric table). The following graph  
shows IBAK as a function of VBAK. These curves are  
useful for calculating backup time when a capacitor  
is used as the VBAK source.  
Although VBAK may be connected to VSS, this is not  
recommended if the companion is used. None of  
the companion functions will operate below  
approximately 2.4V.  
Rev. 1.1  
Apr. 2011  
Page 7 of 26  
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