sh3001imltrt Semtech Corporation, sh3001imltrt Datasheet - Page 8

• Manufacturer Part Number: sh3001imltrt
• Description: Sh3001 Microbuddy Real-time Clock And Clock Management Support Ic For Microcontrollers
• Manufacturer: Semtech Corporation

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.
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.
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.
Copyright ©2002-2005 Semtech Corporation
SYSTEM MANAGEMENT
32.768 kHz
The crystal oscillator has the useful feature of
The default value for load capacitance (12.5 pF)
This adjustment can set the frequency of the crystal
LSB
Fractions
0 - 255
(BIN)
256
1 Hz
Seconds
(BCD)
0 - 59
128
60
Figure 3. Real Time Clock and Periodic Interrupt / Wakeup timer
256 Hz
Minutes
(BCD)
0 - 59
60
(BCD)
0 - 23
Hours
24
16-bit Counter
Days (BIN)
0 - 65535
8
LSB
LSB
Real-Time Clock
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.
179-years of calendar operations (see Figure 3).
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.
absent, if backup power is available.
R
ESET
L
L
OAD
OAD
32-bit Time Interval
32-bit Comparator
Using the ± 4 ppm, 32.768 kHz clock from the LF
The hardware of the Real-Time Clock is capable of
All counting-chain values are loaded at the same
The RTC continues normal operations when V
32-bit Counter
32-bit Latch
32-bit Latch
SH3001 MicroBuddy™
MSB
MSB
V1.15
Current Timer
Interrupt
Value
Serial I/O
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Logic
DD
IO/I
14
is
NT