ELM440

Elm Electronics – Circuits for the Hobbyist

< http://www.elmelectronics.com/ >

Connection Diagram

PDIP and SOIC

(top view)

1

2

3

4

8

7

6

5

60Hz Generator

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.

XT1

XT2

Description

• Stable 60Hz and 1Hz reference sources

• Master oscillator for clock / timekeeping functions

• DC powered backup 60Hz reference signal

Applications

Block Diagram

1 of 4

• 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

Features

ELM440DSB

1Hz

sync

60Hz

2

3

XT1

XT2

5

sync

60Hz

Master

Oscillator

Divider

÷ 60

6

reset

1Hz

7

4

reset