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ELM446 50Hz Generator
Description
The ELM446 is an 8 pin digital divider integrated circuit, that provides both 50Hz 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 50Hz signal. For convenience, a complementary 50Hz signal is also provided. This signal is then further divided to provide a 1Hz signal output. A reset input is provided to restart the internal counters, if desired. An active low signal on this pin will also force all of the outputs to an open or tristate condition.
Features
* Low power CMOS design * Wide supply range - 3.0 to 5.5 volt operation * 3.58MHz crystal controlled operation * Generates both 50Hz and 1Hz references * Low parts count * Complementary 50Hz outputs * High current drive outputs - up to 25 mA
Connection Diagram PDIP and SOIC (top view)
Applications
* Stable 50Hz reference * Master oscillator for clock / timekeeping functions * Decimal based time reference for easier period calculations
VDD XT1 XT2 reset
1 2 3 4 8 7 6 5
VSS 1Hz 50Hz 50Hz
Block Diagram
VDD reset
4
Master Oscillator XT1 XT2
2
Divider
/ 50
7
1Hz
6
50Hz
3 5
50Hz
ELM446DSB
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ELM446
Pin Descriptions
VDD (pin 1) This pin is the positive supply pin, and should always be the most positive point in the circuit. Internal circuitry connected to this pin is used to provide power on reset of the microprocessor, so an external reset signal is not required. Refer to the Electrical Characteristics section for further information. XT1 (pin 2) and XT2 (pin 3) A 3.579545MHz NTSC television colourburst crystal is connected between these two pins. Crystal loading capacitors (typically 27pF) will also normally be connected between each of the pins and VSS. reset (pin 4) This pin can optionally be used to reset the circuit by applying a logic low level to it. While held low, all outputs are placed in an open or tristate condition. If unused, this pin should be left open (as a pullup resistor is provided) or connected to VDD. 50Hz (pin 6) and 50Hz (pin 5) These pins provide complementary 50Hz outputs. Each has a nominal 50% duty cycle. 1Hz (pin 7) The output on this pin is a 1Hz 50% duty cycle signal. VSS (pin 8) Circuit common is connected to this pin. This is the most negative point in the circuit.
Ordering Information
These integrated circuits are available in either the 300 mil plastic DIP format, or in the 200 mil SOIC surface mount type of package. To order, add the appropriate suffix to the part number: 300 mil Plastic DIP............................... ELM446P 200 mil SOIC..................................... ELM446SM
Absolute Maximum Ratings
Storage Temperature....................... -65C to +150C Ambient Temperature with Power Applied....................................-40C to +85C Voltage on VDD with respect to VSS............ 0 to +7.5V Voltage on any other pin with respect to VSS........................... -0.6V to (VDD + 0.6V) Note: Stresses beyond those listed here will likely damage the device. These values are given as a design guideline only. The ability to operate to these levels is neither inferred nor recommended.
All rights reserved. Copyright (c)1999 Elm Electronics. Every effort is made to verify the accuracy of information provided in this document, but no representation or warranty can be given and no liability assumed by Elm Electronics with respect to the accuracy and/or use of any products or information described in this document. Elm Electronics will not be responsible for any patent infringements arising from the use of these products or information, and does not authorize or warrant the use of any Elm Electronics product in life support devices and/or systems. Elm Electronics reserves the right to make changes to the device(s) described in this document in order to improve reliability, function, or design. ELM446DSB
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ELM446
Electrical Characteristics
All values are for operation at 25C and a 5V supply, unless otherwise noted. For further information, refer to note 1 below.
Characteristic
Supply Voltage, VDD VDD rate of rise Average Supply Current, IDD
Minimum
3.0 0.05
Typical
5.0
Maximum Units
5.5 V V/ms
Conditions
see note 2 VDD = 5V VDD = 3V see note 3
0.60 0.35
2.4 2.4 600 0.15 VDD VDD 0.6
mA mA K V V V V
Reset pin internal pullup resistance Input low voltage Input high voltage Output low voltage Output high voltage Output Duty Cycle
300 VSS 0.85 VDD
470
Current (sink) = 8.7mA Current (source) = 5.4mA any output
VDD - 0.7 50
%
Notes:
1. This integrated circuit is produced with a Microchip Technology Inc.'s PIC12C5XX as the core embedded microcontroller. For further device specifications, and possibly clarification of those given, please refer to the appropriate Microchip documentation. 2. This spec must be met in order to ensure that a correct power on reset occurs. It is quite easily achieved using most common types of supplies, but may be violated if one uses a slowly varying supply voltage, as may be obtained through direct connection to solar cells, or some charge pump circuits. 3. The value of the pullup resistance is supply and temperature dependent.
Example Application
+5V 0.1F
Operation of the ELM446 is straightforward, requiring little explanation. Typically it is connected in a circuit as shown at the right. Optionally, one might replace one of the fixed value capacitors with a variable one, in order to be able to trim the oscillator frequency for greater accuracy. As usual, it is also good practice to place a bypass capacitor across the power supply as well.
1 2
8 7 6 5
3.58MHz
3
50Hz Out
27pF
4
27pF
ELM446DSB
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