MIC184
Micrel
MIC184
Local/Remote Thermal Supervisor
General Description
Features
The MIC184 is a versatile digital thermal supervisor capable
of measuring temperature using either its own internal sensor
or an inexpensive external sensor. A 2-wire serial interface is
provided to allow communication with either I2C or SMBus
masters. This device is a pin-for-pin and software compatible
upgrade for the industry standard LM75.
Additional features include remote temperature measurement
capability, and interrupt status and mask bits in the chip’s
configuration register for software polling. The open-drain
interrupt output pin can be used as either an overtemperature
alarm or thermostatic control signal. Three programmable address pins permit users to multidrop up to 8 devices along the
2-wire bus, allowing simple distributed temperature sensing
networks. Superior performance, low power and small size
makes the MIC184 an excellent choice for the most demanding thermal management applications.
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•
•
•
•
•
•
•
•
•
•
•
Measures local and remote temperatures
Pin and software backward compatible to LM75
9-bit sigma-delta ADC
2-wire I2C/SMBus compatible interface
Programmable thermostatic settings for either internal or
external zone
Open-drain comparator/interrupt output pin
Interrupt mask and status bits
Low-power shutdown mode
Fail-safe response to diode faults
2.7V to 5.5V power supply range
Up to 8 devices may share the same bus
8-Lead SOP and MSOP Packages
Applications
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•
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Desktop, Server and Notebook Computers
Printers and Copiers
Test and measurement equipment
Consumer electronics
Ordering Information
Part Number
Temperature Range
Package
MIC184BM
-55°C to +125°C
8-lead SOIC
Pb-FREE
MIC184BMM
-55°C to +125°C
8-lead MSOP
MIC184YM
-55°C to +125°C
8-lead SOIC
X
MIC184YMM
-55°C to +125°C
8-lead MSOP
X
Typical Application
3.0V to 3.6V
VDD
Data
Clock
Interrupt
3×
10k
8
1
2
3
MIC184
VDD
A2/T1
DATA
A1
CLK
INT
A0
GND
5
6
0.1µF
ceramic
7
2200pF
OPTIONAL
REMOTE
TEMPERATURE
SENSOR
4
FROM
SERIAL BUS
HOST
2-Channel SMBus Temperature Measurement System
Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
May 2006
1
MIC184
MIC184
Micrel
Pin Configuration
DATA
1
8 VDD
CLK 2
7 A0
INT 3
6 A1
GND 4
5 A2/T1
Pin Description
Pin Number
Pin Name
Pin Function
1
DATA
Data (Digital I/O): Open-drain. Serial data input/output.
2
CLK
Clock (Digital Input): The host provides the serial bit clock on this input.
3
INT
Interrupt (Digital Output): Open-drain. Interrupt or thermostat output.
4
GND
Ground: Power and signal return for all IC functions.
5
A2/T1
Address Bit 2 (Digital Input): Slave address selection input. See “Slave Address Truth Table.”
Temperature Sensor 1 (Analog Input): Input from remote temperature sensor
(diode junction).
MIC184
6
A1
Address Bit 1 (Digital Input): Slave address selection input. See “Slave Address Truth Table.”
7
A0
Address Bit 0 (Digital Input): Slave address selection input. See “Slave Address Truth Table.”
8
VDD
Supply (Analog Input): Power supply input to the IC.
2
May 2006
MIC184
Micrel
Absolute Maximum Ratings (Note 1)
Operating Ratings (Note 2)
Power Supply Voltage, VDD .......................................... 6.0V
Voltage on Any Pin ................................ –0.3V to VDD+0.3V
Current Into Any Pin ................................................... ±6mA
Power Dissipation, TA = +125°C ................................ 30mW
Junction Temperature .............................................. +150°C
Storage Temperature ................................ –65°C to +150°C
ESD Ratings (Note 3)
Human Body Model ..................................................... 700V
Machine Model ............................................................ 100V
Soldering
Vapor Phase (60 sec.) .............................. +220°C +5⁄–0°C
Infrared (15 sec.) ...................................... +235°C +5⁄–0°C
Power Supply Voltage, VDD ......................... +2.7V to +5.5V
Ambient Temperature Range (TA) ............. -55°C to +125°C
Package Thermal Resistance (θJA)
SOP ................................................................. +152°C/W
MSOP .............................................................. +206°C/W
Electrical Characteristics
2.7V ≤ VDD ≤ 5.5; TA = +25°C, bold values indicate –55°C ≤ TA ≤ +125°C, Note 4; unless noted.
Symbol
Parameter
Condition
Supply Current
Min
Typ
Max
Units
INT open, A2, A1, A0 = VDD or GND,
CLK = DATA = high, normal mode
340
500
µA
shutdown mode, CLK = 100kHz
2.5
Power Supply
IDD
tPOR
Power-On Reset Time
VPOR
Power-On Reset Voltage
VHYST
Power-On Reset
Hysteresis Voltage
µA
INT open, A2, A1, A0 = VDD or GND,
CLK = DATA = high, shutdown mode
1
10
µA
VDD > VPOR
15
100
µs
2.0
2.7
V
all registers reset to default values,
A/D conversions initiated
250
mV
Temperature-to-Digital Converter Characteristics
Accuracy—Local Temperature
Note 5, 6
Accuracy—Remote Temperature
Note 5, 6, 7
tCONV
Conversion Time, Note 5
0°C ≤ TA ≤ +100°C, INT open,
3V ≤ VDD ≤ 3.6V
±1
±2
°C
–55°C ≤ TA ≤ +125°C, INT open,
3V ≤ VDD ≤ 3.6V
±2
±3
°C
0°C ≤ TD ≤ +100°C, INT open,
3V ≤ VDD ≤ 3.6V, 0°C ≤ TA ≤ +85°C
±1
±3
°C
–55°C ≤ TD ≤ +125°C, INT open,
3V ≤ VDD ≤ 3.6V, 0°C ≤ TA ≤ +85°C
±2
±5
°C
local temperature
100
160
ms
remote temperature
200
320
ms
high level
224
400
µA
Remote Temperature Input (T1)
IF
Current to External Diode
Note 5
7.5
low level
14
µA
Address Inputs (A2/T1, A1, A0)
VIL
Low Input Voltage
VIH
High Input Voltage
ILEAK
Input Current
CIN
IPD
May 2006
Input Capacitance
Pulldown Current on A2/T1
2.7V ≤ VDD ≤ 5.5V
2.7V ≤ VDD ≤ 5.5V
0.6
2.0
V
10
±0.01
A2 = VDD, flows for tPOR at power-up
3
V
25
pF
±1
µA
µA
MIC184
MIC184
Symbol
Micrel
Parameter
Condition
Min
Typ
Max
Units
0.4
V
0.8
V
0.3VDD
V
Serial Data I/O Pin (DATA)
VOL
Low Output Voltage
IOL = 3mA
VIL
Low Input Voltage
2.7V ≤ VDD ≤ 5.5V
CIN
Input Capacitance
IOL = 6mA
VIH
High Input Voltage
ILEAK
Input current
VIL
Low Input Voltage
0.7VDD
2.7V ≤ VDD ≤ 5.5V
10
±0.01
V
pF
±1
µA
0.3VDD
V
±1
µA
0.4
V
Serial Clock Input (CLK)
2.7V ≤ VDD ≤ 5.5V
VIH
High Input Voltage
ILEAK
Input current
VOL
Low Output Voltage,
Note 8
tINT
Interrupt Propagation Delay,
Note 5
tnINT
Interrupt Reset Propagation Delay,
Note 5
CIN
0.7VDD
2.7V ≤ VDD ≤ 5.5V
Input Capacitance
10
±0.01
V
pF
Status Output (INT)
T_SET
Default T_SET Value
HYST
Default HYST Value
IOL = 3mA
IOL = 6mA
from TEMP > T_SET, FQ = 00 to INT < VOL,
RPULLUP = 10kΩ; POL bit = 0
from any register read to INT > VOH,
RPULLUP = 10kΩ; POL bit = 0
tPOR after VDD > VPOR, Note 9
tPOR after VDD > VPOR, Note 9
Serial Interface Timing (Note 5)
0.8
V
tCONV+1
µs
1
µs
80
80
80
°C
75
75
75
°C
t1
CLK (Clock) Period
2.5
t2
Data In Setup Time to CLK High
100
ns
t3
Data Out Stable After CLK Low
0
ns
t4
DATA Low Setup Time to CLK Low
start condition
100
ns
t5
DATA High Hold Time
After CLK High
stop condition
100
ns
Note 1.
Exceeding the absolute maximum rating may damage the device.
Note 2.
The device is not guaranteed to function outside its operating rating.
Note 3.
Devices are ESD sensitive. Handling precautions recommended.
Human body model: 1.5k in series with 100pF. Machine model: 200pF, no series resistance.
Note 4.
Final test on outgoing product is performed at TA = TBD°C.
Note 5.
µs
Guaranteed by design over the operating temperature range. Not 100% production tested.
Note 6.
Accuracy specification does not include quantization noise, which may be as great as ±1⁄ 2LSB (±1⁄4°C).
Note 7.
TD 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 8.
Note 9.
Current into the INT pin will result in self-heating of the MIC184. INT pin current should be minimized for best accuracy.
This is the decimal representation of a binary data value.
Timing Diagram
t1
SCL
t4
t5
t2
SDA Input
t3
SDA Output
Serial Interface Timing
MIC184
4
May 2006
MIC184
Micrel
Typical Characteristics
S hutdown I DD
vs . F requenc y
3.5
6
V DD = 5.0V
5
4
V DD = 3.0V
3
2
1
0
0
R es pons e to Immers ion in
125°C F luid B ath
S OIC -8
60
40
20
May 2006
2
fC LOC K = 0Hz
1
0.5
V DD = 3.3V
10
5
TIME (Sec)
15
-60
-40
-20
0
20
40
60
80
100
-10
140
250
200
150
100
50
0
5
-5
300
0
0
Meas urement E rror vs .
P C B L eakage to +5V /+3.3V /G ND
2
4
SUPPLY VOLTAGE (V)
6
Meas urment E rror vs .
C apc itanc e on T 1
G ND
0
80
0
0
2.5
1.5
S upply C urrent
vs . S uppl y V oltage
350
TEMPERATURE (°C)
120 MS OP -8
100
400
V DD = 5.0V
0
50 100 150 200 250 300 350 400
CLOCK FREQUENCY (kHz)
140
MEASURED LOCAL TEMPERATURE (°C)
SHUTDOWN CURRENT (µA)
7
TEMPERATURE (°C)
S hutdown Mode I DD
vs . T emperature
3
MEASUREMENT ERROR (°C)
SHUTDOWN CURRENT (µA)
8
50 f
C LOC K = 0Hz
0
80
100
120
REMOTE DIODE TEMERATURE (°C)
200
150
100
40
60
-60
-40
-20
0
20
40
60
80
100
120
-60
-40
-20
0
20
40
60
80
100
120
140
LOCAL DIODE TEMERATURE (°C)
9
V DD = 3.3V
-4
-5
V DD = 3.3V
300
250
0
20
V DD = 3.3V
-3
V DD = 5.0V
350
-20
-2
-1
-2
-3
Operating I DD
vs . T emperature
-60
-40
-1
1
0
SUPPLY CURRENT (µA)
0
2
-2
3.3V
MEASURMENT ERROR (°C)
1
500
450
400
SUPPLY CURRENT (µA)
MESUREMENT ERROR (°C)
MESUREMENT ERROR (°C)
2
5
4
3
120
140
3
R emote T emperature
Meas urement E rror
140
L oc al T emperature
Meas urement E rror
5.0V
-15
-20
-25
-30
1x10 6
1x10 7
1x10 8
RESISTANCE FROM T1(Ω)
5
1x10 9
-4
-6
-8
-10
-12
0 1 2 3 4 5 6 7 8 9 10
CAPACITANCE (nF)
MIC184
MIC184
Micrel
Functional Diagram
TEMPERATURE-TO-DIGITAL
CONVERTER
2:1
MUX
Bandgap
Sensor
and
Reference
Digital Filter
and
Control
Logic
1-Bit
DAC
Result
Register
A2/T1
A1
A0
2-Wire
Serial Bus
Interface
DATA
Temperature
Setpoint
Register
Temperature
Hysteresis
Register
State
Machine
and
Digital
Comparator
CLK
Configuration
Register
Thermostat
Output
Pointer
Register
INT
MIC184
Functional Description
the address specified in the serial bit stream must be made
to initiate communication. A1 and A0 should be connected
directly to VDD or ground. When A2/T1 is used as an address
bit input, it should also be tied to VDD or ground. A2/T1 can
alternatively connect to a remote temperature sensor. When
A2/T1 is used for temperature measurements, an off-chip diode junction must be connected between A2/T1 and ground. In
this case, internal circuitry will detect A2 as logic low, leaving
four possible slave addresses. See “Temperature Measurement” and “Power On” for more information. A2/T1, A1, and
A0 determine the slave address as shown in Table 1.
Pin Descriptions
VDD
Power supply input. See electrical specifications.
GND
Ground return for all MIC184 functions.
CLK
Clock input to the MIC184 from the two-wire serial bus. The
clock signal is provided by the bus host and is shared by all
devices on the bus.
INT
DATA
Temperature events are indicated to external circuitry via this
output. INT may be configured as active-low or active-high
by the host. Operation of the INT output is controlled by the
MODE and POL bits in the MIC184’s configuration register.
See “Comparator and Interrupt Modes” below. This output
is open-drain and may be wire-ORed with other open-drain
signals. Most systems will require a pull-up resistor or current
source on this pin. If the IM bit in the configuration register
is set, it prevents the INT output from sinking current. In
I2C and SMBus systems, the IM bit is therefore an interrupt
mask bit.
Serial data I/O pin that connects to the two-wire serial bus.
DATA is bidirectional and has an open-drain output driver.
An external pull-up resistor or current source somewhere in
the system is necessary on this line. This line is shared by
all devices on the bus.
A2/T1, A1, A0
These inputs set the three least significant bits of the MIC184’s
7-bit slave address. Each MIC184 will only respond to its own
unique slave address, allowing the use of up to eight MIC184s
on a single bus. A match between the MIC184’s address and
MIC184
6
May 2006
MIC184
Micrel
I n p u ts
A 2 /T 1
A1
against the contents of T_SET and T_HYST. Setting the ZONE
bit in CONFIG will result in the MIC184 acquiring temperature
data from an external diode connected to the A2/T1 pin. This
diode may be embedded in an integrated circuit (such as a
CPU, ASIC, or graphics processor), or it may be a diode-connected discrete transistor. Once the new value is written to
CONFIG, the A/D converter will begin a new conversion and
return temperature data from the external zone. This data
will be compared against T_SET, T_HYST, and the state of
the Fault_Queue (described below). The internal status bit
(STS) and the INT output will then be updated accordingly.
See “Applications Information” for more details on switching
between zones.
Diode Faults
The MIC184 is designed to respond in a fail-safe manner to
hardware faults in the external sensing circuitry. If the connection to the external diode is lost, or the sense line (A2/T1)
is shorted to VDD or ground, the temperature data reported
by the A/D converter will be forced to its full-scale value
(+127.5°C). This will cause an overtemperature event to occur whenever T_SET ≤ +127.0°C (0 1111 1110b). An interrupt
will be generated if so enabled. The temperature reported for
the external zone will remain 0 1111 1111b = +127.5°C until
the fault condition is cleared. This fault detection requires
that the MIC184 complete the number of conversion cycles
specified by Fault_Queue. The MIC184 may therefore require
one or more conversion cycles following power-on or a transition from shutdown to normal operation before reporting an
external diode fault.
Serial Port Operation
The MIC184 uses standard SMBus WRITE_BYTE, READ_
BYTE, WRITE_WORD, and READ_WORD operations for
communication with its host. The SMBus WRITE_BYTE and
WRITE_WORD operations involve sending the device’s slave
address (with the R/W bit low to signal a write operation),
followed by a command byte and one or two data bytes. The
SMBus READ_BYTE operation is similar, but is a composite
write and read operation: the host first sends the device’s
slave address followed by the command byte, as in a write
operation. A new “start” bit must then be sent to the MIC184,
followed by a repeat of the slave address with the R/W bit
(LSB) set to the high (read) state. The data to be read from
MI C 1 8 4 S l a v e A d d r e s s
A0
B ina r y
Hex
0
0
0
100 1000b
48h
0
0
1
100 1001b
49h
0
1
0
100 1010b
4Ah
0
1
1
100 1011b
4B h
1
0
0
100 1100b
4C h
1
0
1
100 1101b
4D h
1
1
0
100 1110b
4E h
1
1
1
100 1111b
4F h
diode
0
0
100 1000b
48h
diode
0
1
100 1001b
49h
diode
1
0
100 1010b
4Ah
diode
1
1
100 1011b
4B h
Table 1. MIC184 Slave Address Settings
Temperature Measurement
The temperature-to-digital converter for both internal and
external temperature data is built around a switched current
source and a 9-bit analog-to-digital converter. The temperature is calculated by measuring the forward voltage of a
diode junction at two different bias current levels. An internal
multiplexer directs the current source’s output to either an
internal or external diode junction.
The MIC184 uses two’s-complement data to represent
temperatures. If the MSB of a temperature value is 0, the
temperature is ≥ 0°C. If the MSB is 1, the temperature is <
0°. More detail on this is given in “Temperature Data Format” below. A temperature event results if the value in the
temperature result register (TEMP) is greater than the value
in the overtemperature setpoint register (T_SET), or if it is
less than the value in the temperature hysteresis register
(T_HYST).
The value of the ZONE bit in the configuration register determines whether readings are taken from the on-chip sensor
or from the A2/T1 input. At power-up, the ZONE bit of the
configuration register is set to zero. The MIC184 therefore
monitors its internal temperature and compares the result
C o m m a n d _ B y te
B ina r y
Hex
0000 0000b
0000 0001b
T a r g e t R e g i s te r
L a be l
D e s c r i p ti o n
00h
T E MP
me a s ure d te mpe ra ture re s ult
01h
C O N F IG
c onfigura tion re gis te r
0000 0010b
02h
T _HY S T
te mpe ra ture hys te re s is
0000 0011b
03h
T _S E T
ove rte mpe ra ture s e tpoint
0000 0100b
04h
re s e rv e d
do not us e
·
·
·
1111 1111b
·
·
·
FFh
Table 2. MIC184 Register Addresses
May 2006
7
MIC184
MIC184
8
CLK
DATA
Data Byte to MIC184
START
ACKNOWLEDGE
ACKNOWLEDGE
Command Byte
MIC184 Slave Address
Figure 1. WRITE_BYTE Protocol
R/W = WRITE
STOP
Data Read From MIC184
NOT ACKNOWLEDGE
MIC184 Slave Address
R/W = WRITE
ACKNOWLEDGE
START
R/W = READ
Command Byte
High-Order Byte to MIC184
Figure 2. READ_BYTE Protocol
ACKNOWLEDGE
NOT ACKNOWLEDGE
Low-Order Byte to MIC184
ACKNOWLEDGE
START
ACKNOWLEDGE
ACKNOWLEDGE
High-Order Byte from MIC184
STOP
Low-Order Byte from MIC184
NOT ACKNOWLEDGE
STOP
START
CLK
DATA
R/W = WRITE
START
R/W = READ
ACKNOWLEDGE
Low-Order Byte from MIC184
ACKNOWLEDGE
START
ACKNOWLEDGE
Master-to-slave transmission
ACKNOWLEDGE
Slave-to-master response
NOT ACKNOWLEDGE
Figure 5. RECEIVE_DATA from a 16-Bit Register
R/W = READ
S 1 0 0 1 A2 A1 A0 1 A D8 D7 D6 D5 D4 D3 D2 D1 A D0 X X X X X X X /A P
High-Order Byte from MIC184
Figure 4. READ_WORD Protocol
ACKNOWLEDGE
MIC184 Slave Address
ACKNOWLEDGE
STOP
NOT ACKNOWLEDGE
S 1 0 0 1 A2 A1 A0 0 A 0 0 0 0 0 0 X X A S 1 0 0 1 A2 A1 A0 1 A D8 D7 D6 D5 D4 D3 D2 D1 A D0 X X X X X X X /A P
MIC184 Slave Address
Figure 3. WRITE_WORD Protocol
ACKNOWLEDGE
Command Byte
R/W = WRITE
S 1 0 0 1 A2 A1 A0 0 A 0 0 0 0 0 0 X X A D8 D7 D6 D5 D4 D3 D0 D1 A D0 X X X X X X X /A P
START
S 1 0 0 1 A2 A1 A0 0 A 0 0 0 0 0 0 X X A S 1 0 0 1 A2 A1 A0 1 A D7 D6 D5 D4 D3 D2 D1 D0 /A P
MIC184 Slave Address
CLK
DATA
CLK
DATA
Command Byte
S 1 0 0 1 A2 A1 A0 0 A 0 0 0 0 0 0 X X A D7 D6 D5 D4 D3 D2 D1 D0 /A P
MIC184 Slave Address
CLK
DATA
MIC184 Slave Address
STOP
MIC184
Micrel
May 2006
May 2006
9
t/INT
START
ACKNOWLEDGE
Command Byte = 01h = CONFIG
STOP
MIC184 Slave Address
CONFIG Value**
New Conversion�
in Progress
tCONV
New Conversion
Result�
Begins
Ready
NOT ACKNOWLEDGE
START
R/W = WRITE
ACKNOWLEDGE
tn/INT
R/W = READ
ACKNOWLEDGE
Master-to-slave transmission
START
Figure 7. Responding to Interrupts
* Assumes INT Polarity is active low.
** Status bits in CONFIG are cleared to zero following this operation.
ACKNOWLEDGE
Slave-to-master response
NOT ACKNOWLEDGE
S 1 0 0 0 A2 A1 A0 0 A 0 0 0 0 0 0 0 1 A S 1 0 0 0 A2 A1 A0 1 A X X X X X X X X /A P
MIC184 Slave Address
Last Byte of Transaction
X X X X X X X X /A P
A/D Converter�
in Standby
ACKNOWLEDGE
…
Figure 6. A/D Converter Timing
Conversion Interrupted
By MIC184 Acknowledge
Conversion�
in Progress
R/W = WRITE
TEMP exceeds T_SET or falls below T_HYST
INT*
DATA
First Byte of Transaction
S 1 0 0 1 A2 A1 A0 1 A X X X X X X X X A
MIC184 Slave Address
STOP
MIC184
Micrel
MIC184
MIC184
Micrel
A/D Converter Timing
Whenever the MIC184 is not in its low power shutdown mode,
the internal A/D converter (ADC) attempts to make continuous
conversions unless interrupted by a bus transaction accessing
the MIC184. When the MIC184 is accessed, the conversion
in progress will be halted, and the partial result discarded.
When the access of the MIC184 is complete the ADC will
begin a new conversion cycle, with results valid tCONV after
that. Figure 6 shows this behavior. tCONV is twice as long for
external conversions as it is for internal conversions. This allows the use of a filter capacitor on the A2/T1 input without a
loss of accuracy due to the resulting longer settling times.
Power-On
When power is initially applied, the MIC184’s internal registers
are set to default states which make the MIC184 completely
backward compatible with the LM75. Also at this time, the
levels on the address inputs A2, A1, and A0 are read to establish the device’s slave address. The MIC184’s power-up
default state can be summarized as follows:
the MIC184 may then be clocked out. There is one exception to this rule: If the location latched in the pointer register
from the last write operation is known to be correct (i.e.,
points to the desired register), then the “RECEIVE_DATA”
procedure may be used. To perform a RECEIVE_DATA, the
host sends an address byte to select the slave MIC184, and
then retrieves the appropriate number (one or two) of data
bytes. Figures 1 through 5 show the formats for these data
read and data write procedures.
The command byte is 8 bits (1 byte) wide. This byte carries
the address of the MIC184 register to be operated upon, and
is stored in the MIC184’s pointer register. The pointer register
is a write-only register, which is implemented for backward
compatibility to the National Semiconductor LM75 and similar
devices. The command byte (pointer register) values corresponding to the various MIC184 register addresses are shown
in Table 2. Command byte values other than 0000 00XXb =
00h through 03h are reserved, and should not be used.
The CONFIG register is 8 bits (1 byte) wide. Therefore, communications with the CONFIG register will at a minimum require
a READ_BYTE, WRITE_BYTE, or a RECEIVE_BYTE.
The TEMP, T_HYST, and T_SET registers are logically
nine bits wide. Note, though, that these registers are physically two bytes (one SMBus word) wide within the MIC184.
Properly communicating with the MIC184 involves a 16-bit
READ_WORD or RECEIVE_WORD from, or WRITE_WORD
to, these registers. This is a requirement of the I2C/SMBus
serial data protocols, which only allow data transfers to occur
in multiples of eight bits.
Temperature Data Format
The LSB of each 9-bit logical register represents 0.5°C. The
values are in a two’s complement format, wherein the most
significant bit (D8) represents the sign: “0” for positive temperatures and “1” for negative temperatures. The seven least
significant bits of each 16-bit physical register are undefined.
Therefore, physical bits D6 through D0 of the data read
from these registers must be masked off, and the resulting
binary value right justified before using the data received.
It is also possible to read only the first byte of any of these
three registers, sacrificing 0.5°C of resolution in exchange
for somewhat simpler data handling. However, all writes
to the T_SET and T_HYST registers must be in the 16-bit
WRITE_WORD format. Table 3 shows examples of the data
format used by the MIC184 for temperatures.
• Normal-mode operation
(MIC184 not in shutdown)
• ZONE is set to internal
(on-chip temperature sensing)
• INT function is set to comparator mode
• INT output is set to active-low operation
• Fault_Queue depth = 1
• Interrupts are enabled (IM = 0)
• T_SET = +80°C; T_HYST = +75°C
In order to accommodate the use of A2/T1 as a dual-purpose
input, there is a weak pulldown on A2/T1 that will attempt to
sink ≈25µA from the pin to ground for tPOR following powerup of the MIC184. This allows the MIC184 to pull A2/T1 to a
low state when a diode junction is connected from that pin
to ground, and latch a zero as the A2 address value. If A2 is
not to be used as a diode connection, it should be connected
to VDD or ground. Note that a fault in the external temperature sensor (if used) may not be reported until one or more
conversion cycles have been completed following power-on.
See DIODE FAULTS.
Shutdown Mode
Setting the SHDN bit in the configuration register halts the
otherwise continuous conversions by the A/D converter. The
T e m p e r a tu r e
R a w B ina r y
Ma s k e d B i n a r y
Ma s k e d H e x
+1 2 5 ° C
0111 1101 0X X X X X X X
0 1111 101 0b
0F Ah
+2 5 ° C
0001 1001 0X X X X X X X
0 0011 001 0b
032h
+0 . 5 ° C
0000 0000 1X X X X X X X
0 0000 000 1b
001h
0° C
0000 0000 0X X X X X X X
0 0000 000 0b
000h
–0. 5° C
1111 1111 1X X X X X X X
1 1111 111 1b
1F F h
–25° C
1110 0111 0X X X X X X X
1 1100 111 0b
1C E h
–40° C
1101 1000 0X X X X X X X
1 1011 000 0b
1B 0h
–55° C
1100 1001 0X X X X X X X
1 1001 001 0b
192h
Table 3. Digital Temperature Format
MIC184
10
May 2006
MIC184
Micrel
MIC184’s power consumption drops to 1µA typical in shutdown
mode. All registers may be read from, or written to, while in
shutdown mode. Serial bus activity will slightly increase the
MIC184’s power consumption.
Entering shutdown mode will not affect the state of INT when
the device is in comparator mode (MODE = 0). However, If
the device is shut down while in interrupt mode, the INT pin
will be deasserted and the internal latch (STS) holding the
interrupt status will be cleared. Therefore, no interrupts will
be generated while the MIC184 is in shutdown mode, and
the interrupt status will not be retained. It is important to
note, however, that the cause of the last temperature event
will be retained in the MIC184. This is described further in
“Comparator and Interrupt Modes” below. The diode fault
detection mechanism (see “Diode Faults”) requires one or
more A/D conversion cycles to detect external sensor faults.
Hence, no diode faults will be detected while the device is
in shutdown.
Comparator and Interrupt Modes
tion, regardless of what caused the last temperature event.
This is done by clearing the MODE bit, and then immediately
resetting it to 1. Following this sequence the next temperature
event detected will be an overtemperature condition, regardless of whether the last temperature event was the result of
an overtemperature or undertemperature condition.
In both modes, the MIC184 will be responsive to overtemperature events upon power up.
Fault_Queue
A Fault_Queue (programmable digital filter) is provided in the
MIC184 to prevent false tripping due to thermal or electrical
noise. Two bits, CONFIG[4:3], set the depth of Fault_Queue.
Fault_Queue then determines the number of consecutive
temperature events (TEMP > T_SET or TEMP < T_HYST)
which must occur in order for the condition to be considered
valid. As an example, assume the MIC184 is in comparator
mode, and CONFIG[4:3] is programmed with 10b. Then the
measured temperature would have to exceed T_SET for four
consecutive A/D conversions before INT would be asserted
or the status bit set. Similarly, TEMP would have to be less
than T_HYST for four consecutive conversions before INT
would be reset.
Like any filter, the Fault_Queue function also has the effect of
delaying the detection of temperature events. In this example,
it would take 4 × tCONV to detect a temperature event. The
depth of Fault_Queue vs. D[4:3] of the configuration register
is shown in Table 4.
Handling Interrupts
The MIC184 may be either polled by the host, or request the
host’s attention via the INT pin. In the case of polled operation, the host periodically reads the contents of CONFIG to
check the state of the status bit. The act of reading CONFIG
clears the status bit, STS. If more than one event that sets
the status bit occurs before the host polls the MIC184, only
the fact that at least one such event has occurred will be
apparent to the host.
If TEMP < T_HYST or TEMP > T_SET for Fault_Queue conversions, the status bit STS will be set in the CONFIG register.
This action cannot be masked. However, a temperature
event will only generate an interrupt signal on INT if interrupts from the MIC184 are enabled (IM = 0 and MODE = 1
in the configuration register). Reading any register following
an interrupt will cause INT to be deasserted, and will clear
STS. The host should read the contents of the configuration
register after receiving an interrupt to confirm that the MIC184
was the source of the interrupt. This is shown in Figure 7.
As noted above, putting the device into shutdown mode will
also deassert INT and clear STS. Therefore, this usually
should not be done before completing the appropriate interrupt service routine(s).
Since temperature-to-digital conversions continue while INT
is asserted, it is possible that temperature could change between the MIC184’s assertion of its INT output and the host’s
response to the interrupt. It is good practice when servicing
interrupts for the host to read the current temperature to confirm
that the condition that caused the interrupt still exists.
Depending on the setting of the MODE bit in the configuration register, the INT output will behave either as an interrupt
request signal or a thermostatic control signal. Thermostatic
operation is known as comparator mode. The INT output is
asserted whenever the measured temperature, as reported
in the TEMP register, exceeds the threshold programmed in
the T_SET register for the number of conversions specified by
Fault_Queue (described below). In comparator mode, INT will
remain asserted unless and until the measured temperature
falls below the value in the T_HYST register for Fault_Queue
conversions. No action on the part of the host is required for
operation in comparator mode. Note that entering shutdown
mode will not affect the state of INT when the device is in
comparator mode.
In interrupt mode, once a temperature event has caused STS
to be set, and the INT output to be asserted, they will not be
automatically deasserted when the measured temperature
falls below T_HYST. They can only be deasserted by reading
any of the MIC184's internal registers or by putting the device
into SHUTDOWN mode. If the most recent temperature event
was an overtemperature condition, STS will not be set again,
and INT cannot be reasserted, until the device has detected
that TEMP < T_HYST. Similarly, if the most recent temperature
event was an undertemperature condition, STS will in be set
again, and INT cannot be reasserted, until the device has
detected that TEMP > T_SET. This keeps the internal logic of
the MIC184 backward compatible with that of the LM75 and
similar devices. There is a software override for this: while
the MIC184 is operating in interrupt mode, the part can be
unconditionally set to monitor for an overtemperature condiC O N F IG [4: 3]
F a u l t_ Q u e u e D e p th
00
1 c onve rs ion*
01
2 c onve rs ions
10
4 c onve rs ions
11
6 c onve rs ions
* D e fa ult s e tting
Table 4. Fault_Queue Depth Settings
May 2006
11
MIC184
MIC184
Micrel
Interrupt Polarity Selection
The INT output can be programmed to behave as an activelow signal or an active-high signal. The default is active-low.
INT polarity is selected by programming the appropriate value
into the polarity bit (POL) in the CONFIG register. Clearing
POL selects active-low interrupts; setting POL selects active-high interrupts. INT is an open-drain digital output and
may be wire-ORed with other open-drain logic signals. Most
applications will require a pull-up resistor on this pin.
Whether the CONFIG register’s POL bit is set to provide a
current-sinking (low) or high-Z (high) state at the INT pin when
STS is high, writing a one to IM will put the INT pin into a highZ state. This meets the requirement of an active-low interrupt
for the SMBus, while making IM available as an INT-forcing
bit for those applications which employ an active-high INT
output (for example, software fan-control routines).
LM75 Compatibility
The MIC184 can be used interchangeably with the LM75 in
existing applications. The MIC184 offers several advantages
MIC184
over the LM75:
• Ability to monitor a second, remote temperature
• Interrupt masking capability
• Status bit for software polling routines
• Lower quiescent current
• Supports single-byte reads from 16-bit registers
• No “inadvertent 8-bit read” bus lock-up issues
The three MSB’s of the configuration register (which power
up as zeroes) are used to access the MIC184’s additional
functions. These are reserved bits according to the LM75
specification and, for the LM75, must always be written as
zeroes. The MSB of the MIC184’s status register is a status
flag that does not exist in the LM75. This bit will be set to one
whenever an overtemperature event occurs. This bit would
never be set by an LM75. Software should not depend on this
bit being zero when using the MIC184 as an LM75 upgrade. If
at power-up the measured temperature is higher than T_SET,
the status bit will be set following the first conversion by the
A/D. See “Applications Information” for a method by which
host software can use this fact to differentiate between an
MIC184 and an LM75.
12
May 2006
MIC184
Micrel
Register Set and Programmer’s Model
Internal Register Set
Na me
D e s c r i p ti o n
C o m m a n d B y te
O p e r a ti o n
P o w e r -U p D e f a u l t
T E MP
me a s ure d te mpe ra ture
00h
9 -bit re a d only
0 0000 0000b
0° C (1)
C O N F IG
c onfigura tion re gis te r
0 1h
8 -bit re a d/write
0000 0000b
( N ote 2 )
T _HY S T
hys te re s is
02 h
9 -bit re a d/write
0 1001 0110b
+7 5 ° C
T _S E T
te mpe ra ture s e tpoint
03 h
9 -bit re a d/write
0 1010 0000b
+8 0 ° C
Detailed Register Descriptions
C O N F I G ( 8 -B i t R e a d /W r i te )
D [7]
D [ 6]
D [ 5]
re a d only
re a d/write
re a d/write
inte rrupt
s ta tus
(S T S )
inte rrupt
ma s k ( 3 )
( I M)
te mp
s e le c t
(ZO N E )
D [ 4]
D [ 3]
D [ 2]
D [ 1]
D [ 0]
re a d/write
re a d/write
re a d/write
re a d/write
fa ult que ue
de pth
(F _Q )
int
pola rity
(P O L )
C MP /I N T
mode
( MO D E )
S hutdown
(S H DN )
B i ts
F u n c ti o n
S TS
inte rrupt s ta tus ( re a d only)
1 = inte rrupt oc c ure d, 0 = none
inte rrupt ma s k
0 = e na ble d, 1 = dis a ble d
inte rna l/re mote te mpe ra ture s e le c tion
1 = re mote , 0 = inte rna l
F _Q
F a ult_ Q ue ue de pth
0 0 = 1 c onve rs ion, 0 1 = 2 c onve rs ions ,
1 0 = 4 c onve rs ions , 1 1 = 6 c onve rs ions
P OL
I N T output pola rity s e le c tion
1 = a c tive high, 0 = a c tive low
MO D E
c ompa ra tor/inte rrupt
mode s e le c tion for I N T pin
1 = inte rrupt mode ,
0 = c ompa ra tor mode
S HDN
norma l/s hutdown
ope ra ting mode s e le c tion
1 = s hutdown,
0 = norma l
IM
ZO NE
O p e r a ti o n
Power-Up Default Value: 0000 0000b = 00h(4)
• not in shutdown mode
• comparator mode
• INT = active low
• Fault_Queue depth = 1
• local temperature zone
• interrupts enabled.
CONFIG Command Byte Address: 0000 0001b = 01h
May 2006
(1) TEMP
will contain measured temperature data for the selected
zone after the completion of one conversion.
(2) After
the first Fault_Queue conversions are complete, the
status bit will be set if TEMP < T_HYST or TEMP > T_SET.
(3) Setting
IM forces the open-drain INT output into its high-Z
state. See “INT Polarity Selection.”
(4) After
the first Fault_Queue conversions are completed, the
status bit will be set if TEMP < T_HYST or TEMP > T_SET.
13
MIC184
MIC184
Micrel
Temperature Result Register
T E MP ( 9 -B i t R e a d O n l y )
D [15]
D [14]
D [13]
D [12]
D [11]
D [10]
D[9]
D [ 8]
D [ 7]
D [ 6]
D [ 5]
D [ 4]
D [ 3]
D [ 2]
D [ 1]
D [ 0]
MS B
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
LS B
X
X
X
X
X
X
X
te mpe ra ture da ta from A D C
B i ts
F u n c ti o n
D [1 5 : 7 ]
O p e r a ti o n
me a s ure d te mpe ra ture da ta
for s e le c te d z one
re a d only*
Power-Up Default Value: 0 0000 0000b = 0°C†
TEMP Command Byte Address: 0000 0000b = 00h
* The value in TEMP is 9 logical bits in width, but due to the
conventions of I2C/SMBus, it is represented by 16 serial bits.
System software should ignore undefined bits D[6:0]. See
“Serial Port Operation" and "Temperature Data Format” for
more details.
†
TEMP will contain measured temperature data for the selected
zone after the completion of one conversion.
Hysteresis Register
T _ H Y S T ( 9 -B i t R e a d /W r i te )
D [15]
D [14]
D [13]
D [12]
D [11]
D [10]
D[9]
D [ 8]
D [ 7]
D [ 6]
D [ 5]
D [ 4]
D [ 3]
D [ 2]
D [ 1]
D [ 0]
MS B
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
LS B
X
X
X
X
X
X
X
te mpe ra ture hys te re s is s e tting
B i ts
F u n c ti o n
D [1 5 : 7 ]
O p e r a ti o n
te mpe ra ture hys te re s is s e tting
re a d/write *
T_HYST Power-Up Default Value: 0 1001 0110b (+75°C)
T_HYST Command Byte Address: 0000 0010b = 02h
* The value in T_HYST is 9 logical bits in width, but due to the
conventions of I2C/SMBus, it is represented by 16 serial bits.
System software should ignore undefined bits D[6:0] during
register reads. Bits [6:0] should be set to zero during register
writes. See "Serial Port Operation" and “Temperature Data
Format” for more details.
Temperature Setpoint Register
T _ S E T ( 9 -B i t R e a d /W r i te )
D [15]
D [14]
D [13]
D [12]
D [11]
D [10]
D[9]
D [ 8]
D [ 7]
D [ 6]
D [ 5]
D [ 4]
D [ 3]
D [ 2]
D [ 1]
D [ 0]
MS B
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
LS B
X
X
X
X
X
X
X
ove rte mpe ra ture s e tpoint
B i ts
D [1 5 : 7 ]
F u n c ti o n
O p e r a ti o n
ove rte mpe ra ture c ompa ra tor s e tpoint
T_SET Power-Up Default Value: 0 1010 0000b (+80°C)
T_SET Command Byte Address: 0000 0011b = 03h
MIC184
re a d/write *
* The value in T_SET is 9 logical bits in width, but due to the
conventions of I2C/SMBus, it is represented by 16 serial bits.
System software should ignore undefined bits D[6:0] during
register reads. Bits [6:0] should be set to zero during register
writes. See Serial Port Operation" and “Temperature Data
Format” for more details.
14
May 2006
MIC184
Micrel
Applications Information
the eight bits of this register are used, and at least one bit
(the MSB) will always return a zero. The MIC184 uses all
eight bits of the CONFIG register: the MSB is the part’s
status bit (STS). A simple test by which the host can
determine whether a system has an MIC184 installed, or
is using a legacy LM75-type device, is to create a situation
which will set the MSB in the MIC184’s CONFIG register
and then determine if the MSB is in fact set. Two examples
of how this can be done are outlined below. The first is interrupt-driven, the second uses software polling. Note that
both procedures generate one or more spurious interrupts.
The code for these tests should therefore temporarily disable any affected interrupt routines.
{START Interrupt-Driven Test and Initialization
Routine}
1. Disable the host’s overtemperature and undertemperature interrupt handling routine. Redirect
interrupts from the part under test to a handler
for the interrupt that will be generated in steps
(4) and (7) of this routine.
Switching Zones
The recommended procedure for switching between the
internal and external zones is as follows:
1. Disable interrupts (if used)
by setting the IM bit in CONFIG.
2. Read the CONFIG register to:
a) Verify no masked interrupt was pending
(D[7] = 0)
b) Clear STS prior to switching zones
c) Hold the settings of CONFIG register for the
current zone
3. Write the appropriate values to
T_SET and T_HYST for the new zone.
4. Write to CONFIG as follows:
a) To toggle the ZONE bit (1 = remote, 0 =
internal)
b) If interrupts are being used, step 4 should
also clear MODE
5. If interrupts are being used, MODE must then be
set to 1 and IM reset to 0
At the conclusion of the serial bus transaction for step 4, the
A/D converter will begin a conversion cycle using the new
zone setting. The next conversion cycle completed after
the serial bus transaction for step 5 will result in the state of
the INT output being updated (if enabled) for the new zone.
Generally the MIC184’s A/D converter operates continuously,
but it will be halted and reset each time the part recognizes
its slave address on the serial bus. Interrupted conversions
will remain halted until the end of the host’s communication
with the MIC184. After the completion of step 5 and a delay
of tCONV x Fault_Queue, STS and INT will contain the results
for the new zone. The above routine is extremely unlikely
to miss a temperature event, as even one A/D conversion is
typically much slower than the I2C/SMBus transactions that
control the MIC184. See Figure 6: A/D Converter Timing.
Step 2(c) is recommended because the MIC184 has only
one CONFIG register, corresponding to the active zone. In
order to preserve data integrity for both zones, 2(c) allows
the host to create a virtual CONFIG register for the inactive
zone by dedicating one byte of memory to that purpose.
Additional virtual registers may be created as needed by
inserting additional reads as steps 2(d), 2(e), etc. These
could for example correspond to the values in T_SET and
T_HYST immediately prior to switching zones. Steps 4(b) and
5 ensure that the MIC184 will enter the new zone searching
for an overtemperature event.
Identifying an MIC184 by Software Test
The MIC184 and the LM75 each have an eight-bit CONFIG register. In LM75-type parts, no more than seven of
May 2006
2. Write 0000 0010b (02h) to the CONFIG register.
(The assumption is made that the host is an I2C
or SMBus part, and therefore responds to an active-low interrupt request.)
3. Write 1100 1000 1000 0000b = C880h to T_SET
and T_HYST. This corresponds to -55.5°C.
4. When the part has finished its first A/D conversion, INT will be asserted.
5. Read out the contents of the CONFIG register:
a) If the part is an MIC184, the MSB will be set
to one (CONFIG = 1000 0010b = 82h).
b) If the part is a conventional LM75-type part,
the MSB will be zero (CONFIG = 0000
0010b = 02h).
6.Write 0111 1111 1000 0000b = 7F80h to T_SET
and T_HYST. This corresponds to +127.5°C.
7.When the part has finished its next A/D conversion, INT will be asserted a second time.
8.Read CONFIG again, to clear the interrupt request from step (7). This will also clear STS, if
the part under test is an MIC184.
9.Based on the results of the test in step (4), do the
following within 50ms total:
a) Set the CONFIG register as required.
b) Load T_HYST with its operational value.
c) Load T_SET with its operational value.
d) Set the host’s interrupt handling routine back
to overtemperature and undertemperature
mode.
{END}
{START Polling-Based Test and Initialization Routine}
1. Temporarily disable the host’s interrupt input
15
MIC184
MIC184
Micrel
from the device under test.
2. Write 0000 0010b (02h) to the CONFIG register.
3. Write 1100 1000 1000 0000b = C880h to T_SET
and T_HYST. This corresponds to -55.5°C.
4. Wait tconv (160ms max.) for the part to finish at
least one A/D conversion.
5. Read the contents of the CONFIG register:
a) If the part is an MIC184, the MSB will be set
to one (CONFIG = 82h).
b) If the part is a conventional LM75-type part,
the MSB will be zero (CONFIG = 02h).
6. Write 0111 1111 1000 0000b = 7F80h to T_SET
and T_HYST. This corresponds to +127.5°C.
7. Wait an additional tconv for the part to finish a
second conversion.
8. Read CONFIG again, to clear the interrupt
request from step (7). This will also clear STS, if
the part under test is an MIC184.
self-heating (VDD × IDD). In order to understand what level of
error this might represent, and how to reduce that error, the
dissipation in the MIC184 must be calculated, and its effects
examined as a temperature error.
In most applications, the INT output will be low for at most a
few milliseconds before the host sets it back to the high state,
making its duty cycle low enough that its contribution to selfheating of the MIC184 is negligible. Similarly, the DATA pin
will in all likelihood have a duty cycle of substantially below
25% in the low state. These considerations, combined with
more typical device and application parameters, allow the
following calculation of typical device self-heating in interrupt-mode:
PD = (IDD(typ.) 3.3V + 25% IOL(data)0.3V +
1% IOL(int)0.3V)
PD = (0.3mA × 3.3V + 25% × 1.5mA × 0.3V +
1% × 1.5mA × 0.3V)
ΔTJ = 1.11mW × 206°C/W
ΔTJ relative to TA is 0.23°C
If the part is to be used in comparator mode, calculations
similar to those shown above (accounting for the expected
value and duty cycle of IOL(int)) will give a good estimate of
the device’s self-heating error.
In any application, the best test is to verify performance
against calculation in the final application environment. This
is especially true when dealing with systems for which some
of the thermal data, (for example, PC board thermal conductivity and/or ambient temperature), may be poorly defined or
unavailable except by empirical means.
Series Resistance
The operation of the MIC184 depends upon sensing the
ΔVCB-E of a diode-connected PNP transistor ("diode") at
two different current levels. For remote temperature measurements, this is done using an external diode connected
between A2/T1 and ground.
Since this technique relies upon measuring the relatively small
voltage difference resulting from two levels of current through
the external diode, any resistance in series with the external
diode will cause an error in the temperature reading from the
MIC184. A good rule of thumb is this: for each ohm in series
with the external transistor, there will be a 0.9°C error in the
MIC184's temperature measurement. It is not difficult to keep
the series resistance well below an ohm (typically 0.1Ω), so
9. Based on the results of the test in step (4), do
the following four steps within 50ms total:
a) Set the CONFIG register as required.
b) Load T_HYST with its operational value.
c) Load T_SET with its operational value.
d) Re-enable the host’s interrupt handling input
from the part under test.
{END}
These routines force the device under test to generate an
overtemperature fault (steps 3 and 4), followed by an undertemperature fault (steps 6 through 8). This sequence causes
the device under test to exit the routine prepared to respond
to an overtemperature condition. If being immediately prepared to detect an undertemperature condition upon exit is
desired, swap steps 3 and 6 in each routine.
Remote Diode Selection
Most small-signal PNP transistors with characteristics similar
to the JEDEC 2N3906 will perform well as remote temperature sensors. Table 3 lists several examples of such parts.
Micrel has tested those marked with a bullet for use with the
MIC184.
Minimizing Errors
Self-Heating
One concern when using a part with the temperature accuracy
and resolution of the MIC184 is to avoid errors induced by
Vendor
Part Number
Package
Tested
Fairchild
MMBT3906
SOT-23
On Semiconductor
MMBT3906L
SOT-23
Phillips Semiconductor
PMBT3906
SOT-23
Rohm Semiconductor
SST3906
SOT-23
Samsung
KST3906-TF
SOT-23
Zetex
FMMT3906
SOT-23
Table 5. Transistors Suitable for Remote Temperature Sensing Use
MIC184
16
May 2006
MIC184
Micrel
in most systems this will not be an issue.
Filter Capacitor Selection
When using a remote diode for temperature sensing, it is
sometimes desirable to use a filter capacitor between the
A2/T1 and GND pins of the MIC184. The use of this capacitor is recommended in environments with a significant high
frequency noise (such as digital switching noise), or if long
wires are used to connect to the remote diode. The maximum
recommended total capacitance from the A2/T1 pin to GND
is 2700pF. This usually suggests the use of a 2200pF NP0
or C0G ceramic capacitor with a 10% tolerance.
If the remote diode is to be at a distance of more than 6" ~
12" from the MIC184, using a shielded cable (solid foil shield
microphone cable is a good choice) for the connections to the
diode can significantly help reduce noise pickup. Remember
to subtract the cable's conductor-to-shield capacitance from
the 2700pF maximum total capacitance.
Layout Considerations
3. When using the MIC184 to sense the temperature of a processor or other device which has an
integral on-board “diode” (e.g., Intel’s Pentium®
III), connect the emitter and base of the remote
sensor to the MIC184 using the guard traces
and Kelvin return shown in Figure 8. The collector of the remote “diode” is inaccessible to
the user on these types of chips. To allow for
this, the MIC184 has superb rejection of noise
appearing from collector to GND, as long as the
base to ground connection is relatively quiet.
4. Due to the small currents involved in the measurement of the remote diode’s ΔVBE, it is
important to adequately clean the PC board after
soldering. This is most likely to show up as an
issue in some situations where water-soluble
soldering fluxes are used.
5. In general, wider traces for the ground and
A2/T1 pins will help reduce susceptibility to radiated noise (wider traces are less inductive). Use
trace widths and spacing of 10 mils wherever
possible. Wherever possible, place a ground
plane under the MIC184, and under the connections from the MIC184 to the remote diode. This
will help guard against stray noise pickup.
6. Always place a good quality VDD bypass capacitor directly adjacent to, or underneath, the
MIC184. This part should be a 0.1µF ceramic
capacitor. Surface-mount parts provide the best
bypassing because of their low inductance.
7. When the MIC184 is being powered from particularly noisy power supplies, or from supplies
which may have sudden high-amplitude spikes
appearing on them, it can be helpful to add additional power supply filtering. This should be
implemented as a 100Ω resistor in series with
the part’s VDD pin, and a 4.7µF, 6.3V electrolytic
capacitor from VDD to GND. See Figure 9.
Local Mode Only Applications:
If the MIC184 is not going to be used with an external diode,
the best layout is one which keeps it thermally coupled to the
subsystem(s) whose temperature it must monitor, while avoiding any strong sources of EMI, RFI, or electrostatically coupled
noise. Two of the most common examples of such sources
are switching power supply transformers and CRTs.
Remote Mode Applications:
1.
If the remote sensing capability of the
MIC184 will be used in an application, place the
MIC184 as close to the remote diode as possible, while taking care to avoid severe noise
sources (high frequency power transformers,
CRTs, memory and data busses, and the like).
2. Since any conductance from the various voltages on the PC Board and the A2/T1 pin can
induce serious errors, it is good practice to guard
the remote diode’s emitter trace with a pair of
ground traces. These ground traces should be
returned to the MIC184’s own ground pin. They
should not be grounded at any other part of their
run. However, it is highly desirable to use these
guard traces to carry the diode’s own ground
return back to the ground pin of the MIC184,
thereby providing a Kelvin connection for the
base of the diode. See Figure 8.
May 2006
17
MIC184
MIC184
Micrel
1 DATA
VDD 8
2 CLK
A0 7
3 INT
A1 6
4 GND
GUARD/RETURN
REMOTE DIODE (A2/T1)
A2/T1 5
GUARD/RETURN
Figure 8. Guard Traces/Kelvin Ground Returns
3.0V to 3.6V
100
0.1F
10k Pull-ups
8
1
FROM
SERIAL BUS
HOST
4.7µF
MIC184
2
3
VDD
DATA
A2/T1
A1
5
CLK
INT
A0
GND
7
6
2200pF
2N3906
4
Figure 9. VDD Decoupling for Very Noisy Supplies
MIC184
18
May 2006
MIC184
Micrel
Package Information
8-Lead SOIC (M)
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May 2006
19
MIC184
MIC184
Micrel
MICREL INC.
2180 FORTUNE DRIVE
SAN JOSE, CA 95131
USA
TEL + 1 (408) 944-0800 FAX + 1 (408) 474-1000 WEB http://www.micrel.com
This information furnished by�
Micrel reserves the right to change circuitry and specifications at any time without notification to the customer.
Micrel Products are not�
reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into
the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchaser's
use or sale of Micrel Pr�
Micrel for any damages resulting from such use or sale.
© 2005 Micrel Incorporated
MIC184
20
May 2006