ELM331 Datasheet, PDF (1/4 Pages) ELM Electronics – Solid State Thermostat

ELM331
Solid State Thermostat
Description
The ELM331 is a complete temperature
measurement and control system in an 8 pin
package.
This integrated circuit is designed to compare
two resistances and drive an output pin depending
on the relative value of each. Typically, one of the
resistors will be an NTC thermistor, and the other
one will be a temperature independent resistor
(whether fixed or variable). When the magnitude of
the resistance connected to pin 2 exceeds the value
of the resistance connected to pin 3, the output pin
will be driven to a high state. Hysteresis maintains
the output in that state until the relative values differ
by approximately 8% (or typically 2°C for a 10KΩ
thermistor).
To reduce the possibility of sporadic outputs, a
condition must exist for three successive cycles, or 6
seconds, before the output pin can change state.
Applications
• Primary thermostat in temperature control
systems
• Staging control for auxiliary heating or cooling
installations
• Under or over temperature alarms
Features
• Low power CMOS design - typically 1mA at 5V
• Wide supply range - 3.0 to 5.5 volt operation
• Built-in proportional hysteresis
• Measurement in progress output
• Time delay on operate improves noise immunity
• Internal pullup resistor on the reset input
• High current drive outputs - up to 25 mA
Connection Diagram
PDIP and SOIC
(top view)
VDD 1
R1 2
R2 3
reset 4
8 VSS
7 Out
6 MIP
5 Cap
Block Diagram
reset ⁴
2
R1
3
R2
5
VDD
Control
Watchdog
Timer
Measurement in Progress (busy)
6 MIP
Overrange
Analog to
Digital
Converter
R1 > R2
3 Consecutive
Measurements
7 Out
ELM331DSB
Elm Electronics – Circuits for the Hobbyist
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