M
Tiny Serial Digital Thermal Sensor
Features
• Digital Temperature Sensing in SOT-23-5 or
TO-220 Packages
• Outputs Temperature as an 8-Bit Digital Word
• Simple SMBus/I
2
C™ Serial Port Interface
• Solid-State Temperature Sensing:
- ±2°C (max.) Accuracy from +25°C to +85°C
- ±3°C (max.) Accuracy from 0°C to +125°C
• Supply Voltage of 2.7V to 5.5V
• Low Power:
- 200 µA (typ.) Operating Current
- 5 µA (typ.) Standby Mode Current
TC74
General Description
The TC74 is a serially accessible, digital temperature
sensor particularly suited for low cost and small form-
factor applications. Temperature data is converted from
the onboard thermal sensing element and made
available as an 8-bit digital word.
Communication with the TC74 is accomplished via a 2-
wire SMBus/I
2
C compatible serial port. This bus also
can be used to implement multi-drop/multi-zone
monitoring. The SHDN bit in the CONFIG register can
be used to activate the low power Standby mode.
Temperature resolution is 1°C. Conversion rate is a
nominal 8 samples/sec. During normal operation, the
quiescent current is 200 µA (typ). During standby
operation, the quiescent current is 5 µA (typ).
Small size, low installed cost and ease of use make the
TC74 an ideal choice for implementing thermal
management in a variety of systems.
Applications
• Thermal Protection for Hard Disk Drives
and other PC Peripherals
• PC Card Devices for Notebook Computers
• Low Cost Thermostat Controls
• Power Supplies
• Thermistor Replacement
Functional Block Diagram
Package Types
TO-220
SDA
5
TC74
123 45
Internal Sensor
(Diode)
SDA
Serial Port
Interface
SCLK
SOT-23
SCLK
4
TC74
1
2
GND
3
V
DD
Temperature
Register
∆Σ
Modulator
Control
Logic
2002 Microchip Technology Inc.
NC
SDA
GND
SCLK
VDD
NC
Note: The TO-220 tab is connected
to pin 3 (GND)
DS21462C-page 1
TC74
1.0
1.1
ELECTRICAL
CHARACTERISTICS
Absolute Maximum Ratings†
Supply Voltage (V
DD
) ............................................ +6V
Voltage On Any Pin ....... (GND – 0.3V) to (V
DD
+ 0.3V)
Current On Any Pin .......................................... ±50 mA
Operating Temperature (T
A
) ........ -40°C
≤
T
A
≤
+125°C
Storage Temperature (T
STG
) .............. -65°C to +150°C
Junction Temperature (T
J
)................................ +150°C
† Notice:
Stresses above those listed under "Maxi-
mum Ratings" may cause permanent damage to the
device. This is a stress rating only and functional oper-
ation of the device at those or any other conditions
above those indicated in the operation listings of this
specification is not implied. Exposure to maximum rat-
ing conditions for extended periods may affect device
reliability.
DC CHARACTERISTICS
Electrical Specifications:
Unless otherwise noted, V
DD
= 3.3V for TC74AX-3.3VXX and
V
DD
= 5.0V for TC74AX-5.0VXX, -40°C
≤
T
A
≤
125°C.
Note 5
Parameters
Power Supply
Power-on Reset Threshold
Supply Voltage
Operating Current
Standby Supply Current
Temperature-to-Bits Converter
Temperature Accuracy
T
ERR
-2.0
-3.0
—
4
0.8 x V
DD
—
—
—
—
-1.0
10
4.7
4.0
—
—
±2.0
8
—
—
—
—
5.0
0.1
—
—
—
+2.0
+3.0
—
—
—
0.2 x V
DD
0.4
0.6
—
1.0
100
—
—
°C
+25°C <T
A
< +85°C
0°C < T
A
< +125°C
-40°C < T
A
< 0°C
Note 2
V
POR
V
DD
I
DD
I
DD-STANDBY
1.2
2.7
—
—
—
—
200
5.0
2.2
5.5
350
10
V
V
µA
µA
V
DD
Falling Edge or Rising
Edge
Note 5
V
DD
= 5.5V,
Note 1
V
DD
= 3.3V
Serial Port Inactive,
Note 4
Sym
Min
Typ
Max
Units
Conditions
Conversion Rate
Serial Port Interface
Logic Input High
Logic Input Low
SDA Output Low
Input Capacitance SDA, SCLK
I/O Leakage
SMBus/I
2
C Clock Frequency
Low Clock Period
High Clock Period
CR
V
IH
V
IL
V
OL
C
IN
I
LEAK
f
SMB
t
LOW
t
HIGH
SPS
V
V
V
V
pF
µA
kHz
µsec
µsec
I
OL
= 3 mA
I
OL
= 6 mA,
Note 3
Serial Port AC Timing (C
LOAD
= 80 pF)
10% to 10%
90% to 90%
Note 1:
Operating current is an average value integrated over multiple conversion cycles. Transient current may
exceed this specification.
2:
Maximum ensured 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 TC74 will
cause self-heating and temperature drift error.
4:
SDA and SCLK must be connected to V
DD
or GND.
5:
V
DD
= 3.3V for TC74AX -3.3 VXX. V
DD
= 5.0V for TC74AX -5.0 VXX. All part types of the TC74 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 V
DD
varies from the nominal value, accuracy will degrade 1°C/V
of V
DD
change.
DS21462C-page 2
2002 Microchip Technology Inc.
TC74
DC CHARACTERISTICS (CONTINUED)
Electrical Specifications:
Unless otherwise noted, V
DD
= 3.3V for TC74AX-3.3VXX and
V
DD
= 5.0V for TC74AX-5.0VXX, -40°C
≤
T
A
≤
125°C.
Note 5
Parameters
SMBus/I
2
C Rise Time
SMBus/I
2
C Fall Time
START Condition Setup Time
(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
Note 1:
2:
3:
4:
5:
Sym
t
R
t
F
t
SU(START)
Min
—
—
4.0
Typ
—
—
—
Max
1000
300
—
Units
nsec
nsec
µsec
Conditions
10% to 90%
90% to10%
90% SCLK to 10% SDA
t
H(START)
t
SU-DATA
t
H-DAT
t
SU(STOP)
t
IDLE
t
POR
4.0
1000
1250
4.0
4.7
—
—
—
—
—
—
500
—
—
—
—
—
—
µsec
nsec
nsec
µsec
µsec
µsec
V
DD
≥
V
POR
(Rising Edge)
Operating current is an average value integrated over multiple conversion cycles. Transient current may
exceed this specification.
Maximum ensured conversion time after Power-on Reset (POR to DATA_RDY) is 250 msec.
Output current should be minimized for best temperature accuracy. Power dissipation within the TC74 will
cause self-heating and temperature drift error.
SDA and SCLK must be connected to V
DD
or GND.
V
DD
= 3.3V for TC74AX -3.3 VXX. V
DD
= 5.0V for TC74AX -5.0 VXX. All part types of the TC74 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 V
DD
varies from the nominal value, accuracy will degrade 1°C/V
of V
DD
change.
2002 Microchip Technology Inc.
DS21462C-page 3
TC74
SMBUS Read Timing Diagram
A
B
t
LOW
t
HIGH
C
D
E F
G
H
I
J
K
SCLK
SDA
t
SU(START)
t
H(START)
t
SU-DATA
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
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
I = Acknowledge Clock Pulse
J = Stop Condition
K = New Start Condition
SMBUS Write Timing Diagram
A
B
t
LOW
t
HIGH
C
D
E F
G
H
I J
K
L
M
SCLK
SDA
t
SU(START)
t
H(START)
t
SU-DATA
t
H-DATA
t
SU(STOP)
t
IDLE
J = Acknowledge Clocked into Master
K = Acknowledge Clock Pulse
L = Stop Condition, Data Executed by Slave
M = New Start Condition
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
FIGURE 1-1:
Timing Diagrams.
DS21462C-page 4
2002 Microchip Technology Inc.
TC74
2.0
PIN DESCRIPTIONS
The descriptions of the pins are listed in Table 2-1.
TABLE 2-1:
Pin No.
(5-Pin
SOT-23)
1
2
3
4
5
PIN FUNCTION TABLE
Pin No.
(5-Pin TO-220)
1
3
5
4
2
Symbol
NC
GND
V
DD
SCLK
SDA
Type
None
Power
Power
Input
Bidirectional
Description
No Internal Connection
System Ground
Power Supply Input
SMBus/I
2
C Serial Clock
SMBus/I
2
C Serial Data
2.1
2.2
Ground (GND)
Power Supply Input (V
DD
)
SMBus/I
2
C Serial Clock (SCLK)
Input. Ground return for all TC74 functions.
Power supply input. See Electrical Specifications.
2.3
Input. SMBus/I
2
C serial clock. Clocks data into and out
of the TC74. See System Management Bus
Specification, Rev. 1.0, for timing diagrams.
2.4
Serial Data (SDA)
Bidirectional. Serial data is transferred on the SMBus/
I
2
C in both directions using this pin. See System
Management Bus Specification, Rev. 1.0 for timing
diagrams.
2002 Microchip Technology Inc.
DS21462C-page 5
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