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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/I2C-compatible serial port. Temperature resolution is 1C. Conversion rate is a nominal 8 samples/sec. Power consumption is only 200 A (5 A Standby). Features * Tested Operating Temperature Range: -40C to +125C * Simple Serial Port Interface * Solid State Temperature Sensing: 2C Accuracy from +25C to +85C 3C Accuracy from 0C to +125C * 3.3V and 5.5V Versions Typical Applications * Thermal Protection for Hard Disk Drives and Other PC Peripherals * Low-Cost Thermostat Controls * Power Supplies
FUNCTIONAL BLOCK DIAGRAM
VDD Internal Sensor (Diode) Serial Port Interface SDA SCL 3 4 SCL
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SOT-23-5 SN SUFFIX CASE TBD PRELIMINARY INFORMATION
PIN CONFIGURATION (Top View)
1 2 5 SDA
NC GND
SOT-23-5*
NOTE: *SOT-23-5 is equivalent to EIAJ-SC74A
DS Modulator
Control Logic
Temperature Register
1 5 TO-220-5 T SUFFIX CASE TBD PRELIMINARY INFORMATION
ORDERING INFORMATION
Device MC74A5-33SNTR MC74A5-50T Package SOT-23-5 TO-220-5 Voltage 3.3V VDD 5.0V VDD
(c) Semiconductor Components Industries, LLC, 1999
1
February, 2000 - Rev. 0
Publication Order Number: MC74/D
MC74
PIN DESCRIPTION FOR TO-220-5
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1 2 3 4 5 NC None Not Connected SDA Bi-directional Power Input SMBus Serial Data System Ground GND SCL SMBus Serial Clock Power Supply Input VDD Power
Pin No.
Symbol
Type
Description
PIN DESCRIPTION FOR SOT-23-5
Pin No. 1 2 3 4 5 Symbol NC Type
Description
None
Not Connected
GND VDD SCL
Power Power Input
System Ground
Power Supply Input
SMBus Serial Clock SMBus Serial Data
SDA
Bi-directional
PIN DESCRIPTION
VDD
SCL
Input. SMBus serial clock. Clocks data into and out of the MC74. See System Management Bus Specification, rev. 1.0, for timing diagrams.
SDA
Input. Power supply input. See electrical specifications.
GND
Input. Ground return for all MC74 functions.
Bi-directional. 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*
Symbol VDD TA Tstg PD Power Supply Voltage Voltage on Any Pin Operating Temperature Range Storage Temperature Range Current on Any Pin Maximum Power Dissipation Parameter Value 6.0 (GND - 0.3 V) to (VDD + 0.3 V) -40 to +125 -65 to +150 50 330 Unit V V C C mA mW
* Maximum Ratings are those values beyond which damage to the device may occur.
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MC74
DC ELECTRICAL CHARACTERISTICS (VDD = 3.3 V or 5.0V (5), -40C TA 125C, unless otherwise noted.) Symbol Power Supply VPOR IDD IDD-STANDBY Power-On Reset Threshold (VDD Falling Edge or Rising Edge) Operating Current (VDD = 5.5V, Serial Port Inactive) (1) Standby Supply Current (VDD = 3.3 V, Serial Port Inactive) (4) V 1.2 -- -- -- 200 5.0 2.2 Characteristic Min Typ Max Unit
mA
350
mA
10
Temperature-to-Bits Converter TERR Temperature Accuracy MC74A +25C TA +85C 0C TA +125C -40C TA 0C Conversion Rate (2) C -2.0 -3.0 -- 4.0 -- -- 2.0 8.0 +2.0 +3.0 -- -- sa/sec
CR
Serial Port Interface VIH VIL VOL Logic Input High Logic Input Low SDA Output Low IOL = 3 mA (3) IOL = 6 mA (3) Input Capacitance SDA, SCL 0.8 x VDD -- -- -- -- -- -- -- -- 5.0 -- 0.2 x VDD 0.4 0.6 -- pF V V V
CIN
ILEAK I/O Leakage -1.0 0.1 1.0 mA 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 VDD or GND. 5. VDD = 3.3V for MC74A5-33SNTR. VDD = 5.0V for MC74A5-50T. All part types of the MC74 will operate properly over the wider power supply range of 2.7V to 5.5V. Each part type is tested and specified for rated accuracy at its nominal supply voltage. As VDD varies from the nominal value, accuracy will degrade 1C/V of VDD change. SERIAL PORT AC TIMING (VDD = 3.3 V or 5.0V, -40C (TA = TJ) 125C; CL = 80 pF unless otherwise noted.) Symbol fSMB tLOW tHIGH tR tF tSU(START) tH(START) tSU-DATA tH-DATA tSU(STOP) tIDLE tPOR 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 (VDD VPOR (Rising Edge)) 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
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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 1C . 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 Explanation Transmitter The device sending data to the bus. Receiver Master 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 transfer 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 (IDD = 5A, 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 Data Valid
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:
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 7 Bits Slave Address WR 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. S = Start Condition P = Stop Condition Shaded = Slave Transmission
Figure 1. SMBus Protocols Acknowledge (ACK)
Start Condition (START)
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.
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MC74
SMBUS Write Timing Diagram
A
ILOW
B
IHIGH
C
D
EF
G
H
I
J
K
L
M
SCL
SDA
t SU(START) t H(START) t SU-DATA t H-DATA t SU(STOP) t IDLE
A = Start Condition B = MSB of Address Clocked into Slave C = LSB of Address Clocked into Slave D = R/W Bit Clocked into Slave E = Slave Pulls SDA Line Low
F = Acknowledge Bit Clocked into Master G = MSB of Data Clocked into Slave H = LSB of Data Clocked into Slave I = Slave Pulls SDA Line Low
J = Acknowledge Clocked into Master K = Acknowledge Clock Pulse L = Stop Condition, Data Executed by Slave M= New Start Condition
SMBUS Read Timing Diagram
A
ILOW
B
IHIGH
C
D
EF
G
H
I
J
K
SCL
SDA
t SU(START) t H(START) t SU-DATA t SU(STOP) t IDLE
A = Start Condition B = MSB of Address Clocked into Slave C = LSB of Address Clocked into Slave D = R/W Bit Clocked into Slave
E = Slave Pulls SDA Line Low F = Acknowledge Bit Clocked into Master G = MSB of Data Clocked into Master H = LSB of Data Clocked into Master
I = Acknowledge Clock Pulse J = Stop Condition K = New Start Condition
Figure 2.
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MC74
REGISTER SET and PROGRAMMER'S MODEL
MC74 Command Set (SMBus READ_BYTE and WRITE_BYTE) Command Byte Description
Command RTR RWCR Code 00h 01h Function Read Temperature (TEMP) Read/Write Configuration (CONFIG)
Temperature Register (TEMP), 8-Bits, READ-ONLY The binary value (2's complement format) in this register represents temperature of the integrated sensor following a conversion cycle. The registers are automatically updated in an alternating manner.
Temperature Register (TEMP)
D[7] MSB D[6] x D[5] x D[4] x D[3] x D[2] x D[1] x D[0] LSB
Configuration Register (CONFIG), 8-BITS, READ/WRITE Configuration Register (Config)
D[7] SHDN Bit D[7] D[6] D[5]--D[0] D[6] Data Rdy POR 0 0 0 D[5] D[4] D[3] D[2] D[1] D[0] Reserved Function STANDBY switch Data Ready* Reserved -- Always returns zero when read. Type Read/ Write Read Only N/A Operation 1 = standby, 0 = normal 1 = ready, 0 = not ready N/A
In the temperature data registers, each unit value represents one degree (Celsius). The value is in 2's-complement binary format such that a reading of 0000 0000b corresponds to 0C. Examples of this temperature to binary value relationship are shown in the following table.
Temperature-to-Digital Value Conversion (TEMP)
ACTUAL TEMPERATURE +130.00C +127.00C +126.50C +25.25C +0.50C +0.25C 0.00C REGISTERED TEMPERATURE +127C +127C +127C +25C +1C 0C 0C 0C 0C -1C -1C -25C -25C -55C -55C -65C BINARY HEX 0111 1111 0111 1111 0111 1111 0001 1001 0000 0001 0000 0000 0000 0000 0000 0000 0000 0000 1111 1111 1111 1111 1110 0111 1110 0110 1100 1001 1100 1001 1011 1111
*DATA_RDY bit reset at power-up and SHDN enable (see below).
V
DD
-0.25C -0.50C -0.75C -1.00C
DATA_RDY
-25.00C -25.25C
SHDN t conv t conv
-54.75C -55.00C -65.00C
Figure 3. . DATA_RDY, SHDN Operation Logic Diagram
Register Set Summary The MC74's register set is summarized below. All registers are 8-bits wide.
Name TEMP Description Internal sensor temperature (2's complement) CONFIG register POR State 0000 0000b* Read Write
CONFIG
0000 0000b
*NOTE: The TEMP register immediately will be updated by the A/D converter after the DATA_RDY bit goes high.
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MC74
TAPING FORM
Component Taping Orientation for 5L SOT-23 Devices
USER DIRECTION OF FEED
DEVICE MARKING
PIN 1
Standard Reel Component Orientation for TR Suffix Device (Mark Right Side Up)
Tape & Reel Specifications Table Package 5L SOT-23 Tape Width (W) 8 mm Pitch (P) 4 mm Part Per Full Reel 3000 Diameter 7 inches
MARKING
SOT-23-5
1
2
3
4
MC74 MC74A5-33SNTR
Marking V5
1
+
2
3
+
4
Date Code
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MC74
PACKAGE DIMENSIONS
SOT-23-5 SNTR SUFFIX PLASTIC PACKAGE CASE TBD ISSUE TBD
0.75 (1.90) REFERENCE
.122 (3.10) .098 (2.50)
.071 (1.80) .059 (1.50)
.020 (0.50) .012 (0.30)
.037 (0.95) REFERENCE .122 (3.10) .106 (2.70)
.057 (1.45) .035 (0.90) .006 (0.15) .000 (0.00) NOTE: SOT-23-5 is equivalent to EIAJ-SC74A
10 MAX.
.010 (0.25) .004 (0.09) .022 (0.55) .008 (0.20) Dimensions: inches (mm)
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MC74
PACKAGE DIMENSIONS
TO-220 T SUFFIX PLASTIC PACKAGE CASE TBD ISSUE TBD
.410 (10.41) .390 (9.91) .156 (3.96) .146 (3.71) DIA. .055 (1.40) .045 (1.14) .185 (4.70) .165 (4.19)
.113 (2.87) .103 (2.62)
.258 (6.55) .230 (5.84) .594 (15.09) .569 (14.45) 3 _ - 7.5 _ 5 PLCS.
.560 (14.22) .518 (13.16)
.037 (0.94) .027 (0.69)
.020 (0.51) .012 (0.30)
.072 (1.83) .062 (1.57) .273 (6.93) .263 (6.68) .115 (2.92) .095 (2.41) Dimensions: inches (mm)
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MC74
Notes
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MC74
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MC74/D

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