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參數(shù)資料
| 型號： | SH3001IMLTRT |
| 元件分類： | 時鐘/數(shù)據(jù)恢復(fù)及定時提取 |
| 英文描述： | REAL TIME CLOCK, QCC16 |
| 封裝： | 3 X 3 MM, 0.90 MM HEIGHT, LEAD FREE, MLP-16 |
| 文件頁數(shù)： | 19/20頁 |
| 文件大?。?/td> | 788K |
| 代理商： | SH3001IMLTRT |
SH3001 MicroBuddy
SYSTEM MANAGEMENT
Copyright 2002-2005 Semtech Corporation
8
V1.15
www.semtech.com
The crystal oscillator has the useful feature of
adjustable load capacitors. It permits tuning of the circuit
for initial tolerance of the crystal (often ± 20 ppm) as well
as an adjustment for the required load capacitance (with
possible variations from the PCB layout). While the
oscillator was designed for a crystal with a nominal load
capacitance of 12.5 pF, the circuit accommodates any
value from ~7 pF to 22 pF (depending on parasitics of
the layout). All of these corrections can be performed
when the part is already installed on the PCB, in the
actual circuit.
The default value for load capacitance (12.5 pF)
loaded on power-up from the factory-programmed
Nonvolatile memory can be re-programmed at any time
(following a secure process of unlocking the load
capacitance value register and immediately writing a
new setting), or it can be completely protected from any
changes by a permanent write-protect flag.
This adjustment can set the frequency of the crystal
oscillator to within ± 4 ppm of the ideal value. As a
reference, a typical 32.768 kHz crystal changes its
frequency 4 ppm for a 10°C change in temperature.
Since the temperature characteristics of crystals are well
known and stable, the host processor is free to
implement an algorithm for temperature compensation of
the crystal oscillator using the adjustable load
capacitors, with resulting accuracy of ± 4 ppm over the
entire temperature range.
Real-Time Clock
Using the ± 4 ppm, 32.768 kHz clock from the LF
oscillator, the Real-Time Clock module keeps time with
a maximum error as low as 2 minutes per year. This
compares favorably with a conventional error of 2
minutes per month for typical RTC chips.
The hardware of the Real-Time Clock is capable of
179-years of calendar operations (see Figure 3).
All counting-chain values are loaded at the same
time into corresponding registers when the Fractions
register is read. All values from registers are loaded into
the counting-chain when the Fractions register is written.
The RTC continues normal operations when VDD is
absent, if backup power is available.
14
Figure 3. Real Time Clock and Periodic Interrupt / Wakeup timer
IO/INT
16-bit Counter
Days (BIN)
0 - 65535
256 Hz
32-bit Time Interval
32-bit Counter
32-bit Comparator
32-bit Latch
Interrupt
Logic
Serial I/O
RESET
÷ 256
÷ 60 ÷ 60 ÷ 24
1 Hz
LSB
MSB
Minutes
(BCD)
0 - 59
Seconds
(BCD)
0 - 59
Fractions
(BIN)
0 - 255
Hours
(BCD)
0 - 23
32-bit Latch
LOAD
LSB
Current Timer
Value
LSB
MSB
32.768 kHz
÷ 128
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