
ELM331
< http://www.elmelectronics.com/ >Connection Diagram
PDIP and SOIC
(top view)
V
DD
V
SS
1
2
3
4
8
7
6
5
Solid State Thermostat
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 10K
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.
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
Primary thermostat in temperature control
systems
Staging control for auxiliary heating or cooling
installations
Under or over temperature alarms
2
3
4
6
7
R
1
R
2
Analog to
Digital
Converter
5
Control
Watchdog
Timer
Cap
MIP
Out
R
1
R
2
reset
3 Consecutive
Measurements
Measurement in Progress (busy)
Overrange
V
DD
Out
MIP
R
1
> R
2
reset
Description
Applications
Block Diagram
1 of 4
Features
ELM331DSB