MC74
Serial Digital
Temperature Sensor
The MC74 is a serial digital temperature sensor suited for low cost
applications. Temperature data is converted from the integrated
thermal sensing element and made available as an 8–bit serial digital
word. Communication with the MC74 is accomplished via 2–wire
SMBus/I
2
C–compatible serial port. Temperature resolution is 1°C.
Conversion rate is a nominal 8 samples/sec. Power consumption is
only 200
µA
(5.0
µA
Standby).
Features
1
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4
2
SOT–23
SN SUFFIX
CASE 1212
•
•
•
•
Temperature Range: –40°C to +125°C
Outputs Temperature as an 8–Bit Digital Word
Simple Serial Port Interface
Solid State Temperature Sensing:
±2°C
Accuracy from +25°C to +85°C
±3°C
Accuracy from 0°C to +125°C
•
3.3 V and 5.5 V Operating Range
•
Low Power
200
µA
Operations
5.0
µA
Standby Mode
Typical Applications
3
TO–220
T SUFFIX
CASE 314D
1
5
•
Thermal Protection for Hard Disk Drives and Other PC Peripherals
•
Low–Cost Thermostat Controls
•
Power Supplies
PIN CONNECTIONS
NC
GND
V
DD
1
2
3
(Top View)
4
SCL
5
SDA
FUNCTIONAL BLOCK DIAGRAM
Internal Sensor
(Diode)
Serial Port
Interface
SDA
SCL
SOT–23A*
NOTE: *SOT–23A is equivalent to EIAJ–SC74A
DS
Modulator
Control
Logic
ORDERING INFORMATION
See detailed ordering and shipping information on page 9 of
this data sheet.
Temperature
Register
DEVICE MARKING INFORMATION
See general marking information in the device marking
section on page 9 of this data sheet.
©
Semiconductor Components Industries, LLC, 2000
1
November, 2000 – Rev. 1
Publication Order Number:
MC74/D
MC74
PIN DESCRIPTION FOR TO–220–5
Pin No.
1
2
3
4
5
Symbol
NC
SDA
GND
SCL
V
DD
Type
None
Bi–directional
Power
Input
Power
Not Connected
SMBus Serial Data
System Ground
SMBus Serial Clock
Power Supply Input
Description
PIN DESCRIPTION FOR SOT–23–5
Pin No.
1
2
3
4
5
Symbol
NC
GND
V
DD
SCL
SDA
Type
None
Power
Power
Input
Bi–directional
Not Connected
System Ground
Power Supply Input
SMBus Serial Clock
SMBus Serial Data
Description
PIN DESCRIPTION
SCL
V
DD
SMBus Serial Clock Input. Clocks data into and out of the
MC74. See System Management Bus Specification, rev. 1.0,
for timing diagrams.
SDA
Power Supply Input. See electrical specifications.
GND
Ground return for all MC74 functions.
Bi–directional Input/Output. Serial data is transferred on
the SMBus in both directions using this pin. See System
Management Bus Specification rev. 1.0 for timing diagrams.
ABSOLUTE MAXIMUM RATINGS*
Rating
Power Supply Voltage
Voltage on Any Pin
Operating Temperature Range
Storage Temperature Range
Current on Any Pin
Package Thermal Resistance
Symbol
V
DD
–
T
A
T
stg
–
R
θJA
Value
6.0
(GND –0.3 V) to (V
DD
+0.3 V)
–40 to +125
–65 to +150
±50
330
Unit
V
V
°C
°C
mA
°C/W
*Maximum Ratings are those values beyond which damage to the device may occur.
*Static–sensitive device. Unused devices must be stored in conductive material. Protect devices from static discharge and static fields. Stresses
above those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only and functional
operation of the device at these or any other conditions above those indicated in the operational sections of the specifications is not implied.
Exposure to Absolute Maximum Rating Conditions for extended periods may affect device reliability.
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MC74
DC ELECTRICAL CHARACTERISTICS
(V
DD
= 3.3 V or 5.0 V (Note 5.), –40°C
≤
T
A
≤
125°C, unless otherwise noted.)
Characteristic
Power Supply
Power–On Reset Threshold
(V
DD
Falling Edge or Rising Edge)
Operating Current
(V
DD
= 5.5V, Serial Port Inactive) (Note 1.)
Standby Supply Current
(V
DD
= 3.3 V, Serial Port Inactive) (Note 4.)
Temperature–to–Bits Converter
Temperature Accuracy MC74A
+25°C
≤
T
A
≤
+85°C
0°C
≤
T
A
≤
+125°C
–40°C
≤
T
A
≤
0°C
Conversion Rate (Note 2.)
Serial Port Interface
Logic Input High
Logic Input Low
SDA Output Low
I
OL
= 3 mA (Note 3.)
I
OL
= 6 mA (Note 3.)
Input Capacitance SDA, SCL
I/O Leakage
V
IH
V
IL
V
OL
–
–
C
IN
I
LEAK
–
–1.0
–
–
5.0
0.1
0.4
0.6
–
1.0
pF
mA
0.8 x V
DD
–
–
–
–
0.2 x V
DD
V
V
V
T
ERR
–2.0
–3.0
–
CR
4.0
–
–
±2.0
8.0
+2.0
+3.0
–
–
sa/sec
°C
V
POR
1.2
I
DD
–
I
DD–STANDBY
–
5.0
10
200
350
mA
–
2.2
mA
V
Symbol
Min
Typ
Max
Unit
SERIAL PORT AC TIMING
(V
DD
= 3.3 V or 5.0 V (Note 5.), –40°C
≤
(T
A
= T
J
)
≤
125°C; C
L
= 80 pF unless otherwise noted.)
Characteristic
SMBus Clock Frequency
Low Clock Period (10% to 10%)
High Clock Period (90% to 90%)
SMBus Rise Time (10% to 90%)
SMBus Fall Time (90% to 10%)
Start Condition Setup Time (90% SCL to 10% SDA)
(for Repeated Start Condition)
Start Condition Hold Time
Data in Setup Time
Data in Hold Time
Stop Condition Setup Time
Bus Free Time Prior to New Transition
Power–On Reset Delay (V
DD
≥
V
POR
(Rising Edge))
Symbol
f
SMB
t
LOW
t
HIGH
t
R
t
F
t
SU(START)
t
H(START)
t
SU–DATA
t
H–DATA
t
SU(STOP)
t
IDLE
t
POR
Min
10
4.7
4.0
–
–
4.0
4.0
1,000
1,250
4.0
4.7
–
Typ
–
–
–
–
–
–
–
–
–
–
–
500
Max
100
–
–
1,000
300
–
–
–
–
–
–
–
Unit
kHz
msec
msec
nsec
nsec
msec
msec
nsec
nsec
msec
msec
msec
1. Operating current is an average value integrated over multiple conversion cycles. Transient current may exceed this specification.
2. Maximum guaranteed conversion time after Power–On RESET (POR to DATA_RDY) is 250 msec.
3. Output current should be minimized for best temperature accuracy. Power dissipation within the MC74 will cause self–heating and
temperature drift error.
4. SDA and SCL must be connected to V
DD
or GND.
5. V
DD
= 3.3 V for MC74–33SNTR. V
DD
= 5.0 V for MC74–50T. All part types of the MC74 will operate properly over the wider power supply
range of 2.7 V to 5.5 V. Each part type is tested and specified for rated accuracy at its nominal supply voltage. As V
DD
varies from the nominal
value, accuracy will degrade 1°C/V of V
DD
change.
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MC74
DETAILED OPERATING DESCRIPTION
The MC74 acquires and converts temperature
information from its integrated solid state sensor with a
basic accuracy of
±1°C
. It stores the data in an internal
register which is read through the serial port. The system
interface is a slave SMBus. The temperature data can be read
at any time through the SMBus port. Eight SMBus addresses
are programmable for the MC74, which allows for a
multi–sensor configuration. Also, there is low–power
Standby mode where temperature acquisition is suspended.
Standby Mode
MC74 Serial Bus Conventions
Term
Transmitter
Receiver
Master
Explanation
The device sending data to the bus.
The device receiving data from the bus.
The device which controls the bus: initiating
transfers (START), generating the clock, and
terminating transfers (STOP).
The device addressed by the master.
A unique condition signaling the beginning of a
transfer indicated by SDA falling (High–Low)
while SCL is high.
A unique condition signaling the end of a trans-
fer indicated by SDA rising (Low–High) while
SCL is high.
A receiver acknowledges the receipt of each
byte with this unique condition. The receiver
drives SDA low during SCL high of the ACK
clock–pulse. The Master provides the clock
pulse for the ACK cycle.
Communication is not possible because the bus
is in use.
When the bus is idle, both SDA and SCL will
remain high.
The state of SDA must remain stable during the
High period of SCL in order for a data bit to be
considered valid. SDA only changes state while
SCL is low during normal data transfers (see
Start and Stop conditions).
Slave
Start
The MC74 allows the host to put it into a low power
(I
DD
= 5.0
µA,
typical) Standby mode. In this mode, the A/D
converter is halted and the temperature data registers are
frozen. The SMBus port operates normally. Standby mode
is enabled by setting the SHDN bit in the CONFIG register.
The table below summarizes this operation.
Standby Mode Operation
SHDN Bit
0
1
Operating Mode
Normal
Standby
Stop
ACK
Busy
NOT Busy
SMBus Slave Address
The MC74 is internally programmed to have a default
SMBus address value of 1001 101b. Seven other addresses
are available by custom order (contact factory).
SERIAL PORT OPERATION
The Serial Clock input (SCL) and bi–directional data port
(SDA) form a 2–wire bi–directional serial port for
programming and interrogating the MC74. The following
conventions are used in this bus architecture:
Data Valid
All transfers take place under control of a host, usually a
CPU or microcontroller, acting as the Master which
provides the clock signal for all transfers. The MC74
always
operates as a Slave. The serial protocol is illustrated in
Figure 1. All data transfers have two phases; all bytes are
transferred MSB first. Accesses are initiated by a start
condition (START), followed by a device address byte and
one or more data bytes. The device address byte includes a
Read/Write selection bit. Each access must be terminated by
a Stop Condition (STOP). A convention called
Acknowledge
(ACK) confirms receipt of each byte. Note
that SDA can change only during periods when SCL is LOW
(SDA changes while SCL is HIGH are reserved for Start and
Stop Conditions).
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MC74
Write Byte Format
S
ADDRESS
7 Bits
Slave Address
Read Byte Format
S
ADDRESS WR
7 Bits
Slave Address
ACK
COMMAND
8 Bits
WR
ACK
COMMAND
8 Bits
ACK
DATA
8 Bits
ACK
P
Command Byte: selects
which register you are
writing to.
ACK
S
ADDRESS RD
7 Bits
Data Byte: data goes
into the register set
by the command byte.
ACK
DATA
8 Bits
NACK
P
Command Byte: selects
which register you are
reading from.
Slave Address: repeated
due to change in data–
flow direction.
Data Byte: reads from
the register set by the
command byte.
Receive Byte Format
S
ADDRESS RD
7 Bits
ACK
DATA
8 Bits
NACK
P
Data Byte: reads data from
the register commanded by
the last Read Byte or Write
Byte transmission.
S = Start Condition
P = Stop Condition
Shaded = Slave Transmission
Figure 1. SMBus Protocols
Start Condition (START)
Acknowledge (ACK)
The MC74 continuously monitors the SDA and SCL lines
for a start condition (a HIGH to LOW transition of SDA
while SCL is HIGH) and will not respond until this condition
is met.
Address Byte
Immediately following the Start Condition, the host must
transmit the address byte to the MC74. The states of A1 and
A0 determine the 7–bit SMBus address for the MC74. The
7–bit address transmitted in the serial bit stream must match
for the MC74 to respond with an Acknowledge (indicating
the MC74 is on the bus and ready to accept data). The eighth
bit in the Address Byte is a Read–Write Bit. This bit is a 1
for a read operation or 0 for a write operation. During the
first phase of any transfer this bit will be set = 0 to indicate
that the command byte is being written.
Acknowledge (ACK) provides a positive handshake
between the host and the MC74. The host releases SDA after
transmitting eight bits, then generates a ninth clock cycle to
allow the MC74 to pull the SDA line LOW to acknowledge
that it successfully received the previous eight bits of data or
address.
Data Byte
After a successful ACK of the address byte, the host must
transmit the data byte to be written or clock out the data to
be read. (See the appropriate timing diagrams. ) ACK will
be generated after a successful write of a data byte into the
MC74.
Stop Condition (STOP)
Communications must be terminated by a stop condition
(a LOW to HIGH transition of SDA while SCL is HIGH).
The Stop Condition must be communicated by the
transmitter to the MC74. NOTE: Refer to Timing Diagrams
for serial bus timing (Figure 2).
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