ELM440
60Hz Generator
Description
Features
The ELM440 is an 8 pin digital divider integrated
• Low power CMOS design
circuit, that provides both 60Hz and 1Hz outputs
from a common 3.58MHz NTSC colourburst crystal.
• Wide supply range - 3.0 to 5.5 volt operation
• Generates both 60Hz and 1Hz references
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.
• 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
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.
• High current drive outputs - up to 25 mA
Connection Diagram
PDIP and SOIC
(top view)
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.
1
2
3
4
8
7
6
5
VDD
VSS
XT1
XT2
60Hz
1Hz
Applications
• Stable 60Hz and 1Hz reference sources
• Master oscillator for clock / timekeeping functions
• DC powered backup 60Hz reference signal
sync
reset
Block Diagram
5
sync
7
6
60Hz
1Hz
Master
Oscillator
Divider
÷ 60
2
3
XT1
XT2
VDD
4
reset
ELM440DSB
Elm Electronics – Circuits for the Hobbyist
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