Rainbow Electronics LM27 - Manual

LM27
SOT-23,
± 3˚C Accurate, 120˚C-150˚C Factory Preset
Thermostat
General Description
The LM27 is a precision, single digital-output, low-power
thermostat comprised of an internal reference, DAC, tem-
perature sensor and comparator. Utilizing factory program-
ming, it can be manufactured with different trip points as well
as different digital output functionality. The trip point (T
OS
)
can be preset at the factory to any temperature in the range
of +120˚C to +150˚C in 1˚C increments. The LM27 has one
digital output (OS/OS/US/US), one digital input (HYST) and
one analog output (V
TEMP
). The digital output stage can be
preset as either open-drain or push-pull. In addition, it can be
factory programmed to be active HIGH or LOW. The digital
output can be factory programmed to indicate an over tem-
perature shutdown event (OS or OS) or an under tempera-
ture shutdown event (US or US). When preset as an over-
temperature shutdown (OS) it will go LOW to indicate that
the die temperature is over the internally preset T
OS
and go
HIGH when the temperature goes below (T
OS
–T
HYST
). Simi-
larly, when preprogrammed as an undertemperature shut-
down (US) it will go HIGH to indicate that the temperature is
below T
US
and go LOW when the temperature is above
(T
US
+T
HYST
). The typical hysteresis, T
HYST
, can be set to
2˚C or 10˚C and is controlled by the state of the HYST pin. A
V
TEMP
analog output provides a voltage that is proportional
to temperature and has a −10.7mV/˚C output slope.
Currently, there are several standard parts available, see
ordering information for details. For other part options, con-
tact a National Semiconductor Distributor or Sales Repre-
sentative for information on minimum order qualification. The
LM27 is currently available in a 5-lead SOT-23 package.
Applications
n Microprocessor Thermal Management
n Appliances
n Portable Battery Powered Systems
n Fan Control
n Industrial Process Control
n HVAC Systems
n Electronic System Protection
Features
n Internal comparator with pin selectable 2˚C or 10˚C
hysteresis
n No external components required
n Open-drain or push-pull digital output; supports CMOS
logic levels
n Internal temperature sensor with V
TEMP
output pin
n V
TEMP
output allows after-assembly system testing
n Internal voltage reference and DAC for trip-point setting
n Currently available in 5-pin SOT-23 plastic package
n Excellent power supply noise rejection
Key Specifications
j Power Supply Voltage 2.7V to 5.5V
j Power Supply Current 40µA(max)
15µA(typ)
j Hysteresis Temperature 2˚C or 10˚C(typ)
j Temperature Trip Point Accuracy ± 3˚C (max)
LM27CIM5-2HJ Simplified Block Diagram and Connection Diagram
20030701
The LM27CIM5-2HJ has a fixed trip point of 140˚C.
For other trip point and output function availability,
please see ordering information or contact National Semiconductor.
August 2002
LM27
SOT
-23,
±
3˚C
Accurate,
120˚C-150˚C
Factory
Preset
Thermostat
© 2002 National Semiconductor Corporation DS200307 www.national.com