MIC281
Micrel
MIC281
Low-Cost IttyBitty™ Thermal Sensor
Final Information
General Description
The MIC281 is a digital thermal sensor capable of measuring
the temperature of a remote PN junction. It is optimized for
applications favoring low cost and small size. The remote
junction may be an inexpensive commodity transistor, e.g.,
2N3906, or an embedded thermal diode such as found in Intel
Pentium* II/III/IV CPUs, AMD Athlon* CPUs, and Xilinx
Virtex* FPGAs.
The MIC281 is 100% software and hardware backward
compatible with the MIC280 and features the same industry-
leading noise performance and small size. The advanced
integrating A/D converter and analog front-end reduce errors
due to noise for maximum accuracy and minimum
guardbanding.
A 2-wire SMBus 2.0-compatible serial interface is provided
for host communication. The clock and data pins are 5V-
tolerant regardless of the value of V
DD
. They will not clamp
the bus lines low even if the device is powered down.
Superior performance, low power, and small size make the
MIC281 an excellent choice for cost-sensitive thermal man-
agement applications.
Features
• Remote temperature measurement using embedded
thermal diodes or commodity transistors
• Accurate remote sensing
±3°C
max., 0°C to 100°C
• Excellent noise rejection
• I
2
C and SMBus 2.0 compatible serial interface
• SMBus timeout to prevent bus lockup
• Voltage tolerant I/Os
• Low power shutdown mode
• Failsafe response to diode faults
• 3.0V to 3.6V power supply range
• IttyBitty™ SOT23-6 Package
Applications
•
•
•
•
Desktop, server and notebook computers
Set-top boxes
Game consoles
Appliances
Typical Application
3.3V
10k
pull-ups
5
TO
SERIAL BUS
HOST
4
0.1µF
MIC281
VDD
T1
GND
1
3
2
DATA
CLK
NC
2000pF
CPU DIODE
MIC281 Typical Application
IttyBitty is a trademark of Micrel, Inc.
*All trademarks are the property of their respective owners.
Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 944-0970 • http://www.micrel.com
August 2002
1
MIC281
MIC281
Micrel
Ordering Information
Part Number
MIC281-0BM6*
MIC281-1BM6*
MIC281-2BM6*
MIC281-3BM6*
MIC281-4BM6
MIC281-5BM6*
MIC281-6BM6*
MIC281-7BM6*
Marking
TB00
TB01
TB02
TB03
TB04
TB05
TB06
TB07
Slave Address
1001 000x
b
1001 001x
b
1001 010x
b
1001 011x
b
1001 100x
b
1001 101x
b
1001 110x
b
1001 111x
b
Ambient Temperature Range
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
Package
SOT23-6
SOT23-6
SOT23-6
SOT23-6
SOT23-6
SOT23-6
SOT23-6
SOT23-6
* Contact Micrel regarding availability.
Pin Configuration
VDD 1
GND 2
T1 3
6 NC
5 DATA
4 CLK
SOT23-6
Pin Description
Pin
1
2
3
4
5
6
Pin Name
VDD
GND
T1
CLK
DATA
NC
Pin Description
Analog Input: Power supply input to the IC.
Ground return for all IC functions.
Analog Input: Connection to remote diode junction.
Digital Input: Serial bit clock input.
Digital I/O: Open-drain. Serial data input/output.
No Connection: Must be left unconnected.
MIC281
2
August 2002
MIC281
Micrel
Absolute Maximum Ratings
(Note 1)
Power Supply Voltage, V
DD ...................................................
3.8V
Voltage on T1 ........................................ –0.3V to V
DD
+0.3V
Voltage on CLK, DATA ................................. –0.3V to 6.0V
Current Into Any Pin .................................................
±10mA
Power Dissipation, T
A
= 125°C ............................... 109mW
Junction Temperature ............................................... 150°C
Storage Temperature ............................... –65°C to +150°C
ESD Ratings,
Note 7
Human Body Model ................................................ 1.5kV
Machine Model ........................................................ 200V
Soldering (SOT23-6 Package)
Vapor Phase (60s) ........................................ 220
+5
/
–0
°C
Infrared (15s) ................................................. 235
+5
/
–0
°C
Operating Ratings
(Note 2)
Power Supply Voltage, V
DD ..............................
+3.0V to +3.6V
Ambient Temperature Range (T
A
) ............. –40°C to +85°C
Package Thermal Resistance (θ
JA
)
SOT-23-6 .......................................................... 230°C/W
Electrical Characteristics
For typical values, T
A
=25°C, V
DD
=3.3V unless otherwise noted.
Bold
values are for T
MIN
≤
T
A
≤
T
MAX
unless otherwise noted.
Note 2
Symbol
Power Supply
I
DD
Supply Current
T1 open; CLK=DATA=High; Normal Mode
Shutdown mode; T1 open; CLK = 100kHz;
Note 5
Shutdown Mode; T1 open; CLK=DATA=High
t
POR
V
POR
V
HYST
Power-on reset time,
Note 5
Power-on reset voltage
Power-on reset hysteresis voltage
Note 5
0°C
≤
T
D
≤
100°C; 0°C
≤
T
A
≤
85°C;
3.15V
≤
V
DD
≤
3.45V
–40°C
≤
T
D
≤
125°C; 0°C
≤
T
A
≤
85°C;
3.15V
≤
V
DD
≤
3.45V
t
CONV
I
F
Conversion time,
Note 5
Remote Temperature Input, T1
Current into External Diode
Note 5
Serial Data I/O Pin, DATA
V
OL
V
IL
V
IH
C
IN
I
LEAK
Low Output Voltage,
Note 4
I
OL
= 3mA
I
OL
= 6mA
Low Input Voltage
High Input Voltage
Input Capacitance,
Note 5
Input Current
3.0V
≤
V
DD
≤
5.5V
3.0V
≤
V
DD
≤
5.5V
2.1
10
±1
0.3
0.5
0.8
5.5
V
V
V
V
pF
µA
T1 forced to 1.0V, high level
Low level
7
192
12
400
µA
µA
V
DD
> V
POR
All registers reset to default values; A/D
conversions initiated
0.23
9
6
200
2.65
300
2.95
0.4
mA
µA
µA
µs
V
mV
Parameter
Condition
Min
Typ
Max
Units
Temperature-to-Digital Converter Characteristics
Accuracy,
Notes 3, 5, 6
±1
±2
200
±3
±5
240
°C
°C
ms
August 2002
3
MIC281
MIC281
Symbol
Parameter
Condition
3.0V
≤
V
DD
≤
3.6V
3.0V
≤
V
DD
≤
3.6V
2.1
10
Min
Typ
Max
Micrel
Units
Serial Clock Input, CLK
V
IL
V
IH
C
IN
I
LEAK
t
1
t
2
t
3
t
4
t
5
t
TO
Low Input Voltage
High Input Voltage
Input Capacitance,
Note 5
Input current
0.8
5.5
V
V
pF
µA
µs
ns
ns
ns
ns
30
35
ms
±
1
2.5
100
300
Start Condition
Stop Condition
100
100
25
Serial Interface Timing
CLK (clock) period
Data in Setup Time to CLK High
Data Out Stable After CLK Low
DATA Low Setup Time to CLK Low
DATA High Hold Time After CLK High
Bus timeout
Note 1.
The device is not guaranteed to function outside its operating range.
Note 2.
Final test on outgoing product is performed at T
A
= 25°C.
Note 3.
T
D
is the temperature of the remote diode junction. Testing is performed using a single unit of one of the transistors listed in Table 5.
Note 4.
Current into the DATA pin will result in self-heating of the device. Sink current should be minimized for best accuracy.
Note 5.
Guaranteed by design over the operating temperature range. Not 100% production tested.
Note 6.
Accuracy specifications do not include quantization noise which may be up to
±
0.5LSB.
Note 7.
Devices are ESD sensitive. Observe appropriate handling precautions.
Timing Diagram
t
1
SCL
t
4
SDA
DATA INPUT
SDA
DATA OUTPUT
t
2
t
3
t
5
Serial Interface Timing
MIC281
4
August 2002
MIC281
Micrel
Typical Characteristics
V
DD
= 3.3V; T
A
= 25°C, unless otherwise noted.
Remote Temperature
Measurement Error
2
MEASUREMENT ERROR (°C)
SUPPLY CURRENT (µA)
1.5
1
0.5
0
-0.5
-1
-1.5
-2
0
20
40
60
80
100
REMOTE DIODE TEMPERATURE (°C)
400
350
300
250
200
150
100
50
0
-55 -35 -15 5 25 45 65 85 105125
TEMPERATURE (°C)
Supply Current vs.
Temperature for V
DD
= 3.3V
QUIESCENT CURRENT (µA)
20
Quiescent Current vs.
Clock Frequency in
Shutdown Mode
T1 open
DATA = HIGH
15
10
5
0
0
100
200
300
FREQUENCY (kHz)
400
Quiescent Current vs.
Temperature in Shutdown Mode
30
QUIESCENT CURRENT (µA)
T1 open
25 CLK = DATA = HIGH
20
15
10
5
0
-55 -35 -15 5 25 45 65 85 105125
TEMPERATURE (°C)
Quiescent Current vs.
Supply Voltage in Shutdown Mode
10
9
8
7
6
5
4
3
2
1
0
2.6
2.8
3.0
3.2
3.4
SUPPLY VOLTAGE (V)
3.6
MEASUREMENT ERROR (°C)
QUIESCENT CURRENT (µA)
T1 open
CLK = DATA = HIGH
Measurement Error vs.
PCB Leakage to +3.3V/GND
8
6
4
2
0
-2
-4
-6
-8
1x10
7
1x10
8
1x10
9
1x10
6
RESISTANCE FROM T1 (Ω)
3.3V
GND
Remote Temperature Error vs.
Capacitance on T1
5
Error Due to Noise on the Base
of Remote Transistor
7
REMOTE TEMP. ERROR (°C)
TEMPERTURE ERROR (°C)
6
5
4
3
2
1
10mV
P-P
3mV
P-P
25mV
P-P
Error Due to Noise on the
Collector of Remote Transistor
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
25mV
P-P
0
1 10 100 1k 10k100k 1M 10M100M
FREQUENCY (Hz)
50mV
P-P
100mV
P-P
TEMPERATURE ERROR (°C)
0
-5
-10
-15
-20
1000
2000
3000
4000
5000
6000
7000
CAPACITANCE (pF)
August 2002
8000
0
1 10 100 1k 10k100k 1M 10M100M
FREQUENCY (Hz)
0
5
MIC281
