ELM440
60Hz Generator
Description
The ELM440 is an 8 pin digital divider integrated
circuit, that provides both 60Hz and 1Hz outputs
from a common 3.58MHz NTSC colourburst crystal.
Externally, the designer need only provide the
crystal and two appropriate loading capacitors, as
well as a suitably bypassed power supply. Internal
oscillator circuits then use this reference frequency
to precisely derive a stable 60Hz signal. This signal
is then further divided to provide a 1Hz output.
The ELM440 can also be locked in synchronism
to an external 60 or 120 Hz line frequency signal. If
derived from the electrical grid voltage, this results in
excellent long-term stability, as the power generation
frequency is traceable to national standards. The
transition to or from sync-lock with this external
signal occurs automatically.
A reset input is also provided to restart the
internal counters, if desired. An active low signal on
this pin will force both outputs to an open or tristate
condition.
Features
• Low power CMOS design
• Wide supply range - 3.0 to 5.5 volt operation
• Generates both 60Hz and 1Hz references
• Automatically synchronizes to the line frequency
for long term stability, when it’s available
• Uses a standard 3.58MHz crystal for the time
reference if there is no sync input
• High current drive outputs - up to 25 mA
Connection Diagram
PDIP and SOIC
(top view)
V
DD
XT1
XT2
reset
1
2
3
4
8
7
6
5
V
SS
60Hz
1Hz
sync
Applications
• Stable 60Hz and 1Hz reference sources
• Master oscillator for clock / timekeeping functions
• DC powered backup 60Hz reference signal
Block Diagram
sync
5
7
60Hz
Master
Oscillator
XT1
XT2
2
Divider
÷ 60
6
1Hz
V
DD
3
4
reset
ELM440DSB
Elm Electronics – Circuits for the Hobbyist
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