MIC184
Micrel
MIC184
Local/Remote Thermal Supervisor
Advance Information
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 opendrain 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.
•
•
•
•
•
•
•
•
•
•
•
•
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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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 SOP
MIC184BMM
–55°C to +125°C
8-lead MSOP
Typical Application
3.0V to 3.6V
VDD
Data
3×
10k
MIC184
8
1
Clock
2
Interrupt
3
VDD
DATA
CLK
INT
A2/T1
A1
A0
5
GND
4
6
0.1µF
ceramic
7
2200pF
OPTIONAL
REMOTE
TEMPERATURE
SENSOR
FROM
SERIAL BUS
HOST
2-Channel SMBus Temperature Measurement System
Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 944-0970 • http://www.micrel.com
November 2000
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
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.”
Data (Digital I/O): Open-drain. Serial data input/output.
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
November 2000
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 .................................................. TBD V
Machine Model ......................................................... TBD V
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
TBD
µA
shutdown mode, CLK = 100kHz
2.5
Power Supply
IDD
µA
INT open, A2, A1, A0 = VDD or GND,
CLK = DATA = high, shutdown mode
1
TBD
µA
tPOR
Power-On Reset Time
VDD > VPOR
15
100
µs
VPOR
Power-On Reset Voltage
all registers reset to default values,
A/D conversions initiated
2.0
2.7
V
VHYST
Power-On Reset Hysteresis Voltage
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
low level
7.5
µA
14
Address Inputs (A2/T1, A1, A0)
VIL
Low Input Voltage
2.7V ≤ VDD ≤ 5.5V
VIH
High Input Voltage
2.7V ≤ VDD ≤ 5.5V
CIN
Input Capacitance
ILEAK
Input Current
IPD
Pulldown Current on A2/T1
November 2000
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
IOL = 3mA
0.4
V
IOL = 6mA
0.8
V
0.3VDD
V
Serial Data I/O Pin (DATA)
VOL
Low Output Voltage
VIL
Low Input Voltage
2.7V ≤ VDD ≤ 5.5V
VIH
High Input Voltage
2.7V ≤ VDD ≤ 5.5V
CIN
Input Capacitance
ILEAK
Input current
0.7VDD
V
10
±0.01
pF
±1
µA
0.3VDD
V
Serial Clock Input (CLK)
VIL
Low Input Voltage
2.7V ≤ VDD ≤ 5.5V
VIH
High Input Voltage
2.7V ≤ VDD ≤ 5.5V
CIN
Input Capacitance
ILEAK
Input current
0.7VDD
V
10
pF
±1
µA
IOL = 3mA
0.4
V
IOL = 6mA
0.8
V
tCONV+1
µs
1
µs
±0.01
Status Output (INT)
VOL
Low Output Voltage,
Note 8
tINT
Interrupt Propagation Delay,
Note 5
from TEMP > T_SET, FQ = 00 to INT < VOL,
RPULLUP = 10kΩ; POL bit = 0
tnINT
Interrupt Reset Propagation Delay,
Note 5
from any register read to INT > VOH,
RPULLUP = 10kΩ; POL bit = 0
T_SET
Default T_SET Value
tPOR after VDD > VPOR, Note 9
80
80
80
°C
HYST
Default HYST Value
tPOR after VDD > VPOR, Note 9
75
75
75
°C
Serial Interface Timing (Note 5)
t1
CLK (Clock) Period
2.5
µs
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.
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.
Current into the INT pin will result in self-heating of the MIC184. INT pin current should be minimized for best accuracy.
Note 9.
This is the decimal representation of a binary data value.
Timing Diagram
t1
SCL
t4
t2
t5
SDA Input
t3
SDA Output
Serial Interface Timing
MIC184
4
November 2000
MIC184
Micrel
Typical Characteristics
Remote Temperature
Measurement Error
TEMPERATURE (°C)
Shutdown IDD
vs. Frequency
Shutdown Mode IDD
vs. Temperature
Shutdown Mode IDD
vs. Suply Voltage
2
1
Response to Immersion in
125°C Fluid Bath
-60
VDD = 3.3V
250
200
150
100
0
0
40
20
5
10
TIME (Sec)
15
6
0
GND
0
-5
2
4
SUPPLY VOLTAGE (V)
Measurment Error vs.
Capcitance on T1
Measurement Error vs.
PCB Leakage to +5V/+3.3V/GND
3.3V
5.0V
-10
-15
-20
-25
-30
1x106
1x107
1x108
1x109
RESISTANCE FROM T1(Ω)
5
MEASURMENT ERROR (°C)
60
50
TEMPERATURE (°C)
MEASUREMENT ERROR (°C)
SOIC-8
80
November 2000
0.5
300
5
120 MSOP-8
0
0
1
0
140
100
QUIESCENT CURRENT (µA)
3
fCLOCK = 0Hz
1.5
350
120
140
VDD = 3.0V
100
4
2
60
80
5
2.5
40
VDD = 5.0V
0
20
6
3
-20
7
400
VDD = 5.0V
-40
SHUTDOWN CURRENT (µA)
3.5
8
120
140
100
60
80
0
20
-20
50 f
CLOCK = 0Hz
0
40
150
100
-60
SUPPLY CURRENT (µA)
VDD = 3.3V
250
200
120
140
100
60
80
120
140
100
60
80
40
-4 VDD = 3.3V
-5
350
300
REMOTE DIODE TEMERATURE (°C)
0
0 50 100 150 200 250 300 350 400
CLOCK FREQUENCY (kHz)
MEASURED LOCAL TEMPERATURE (°C)
-2
-3
VDD = 5.0V
LOCAL DIODE TEMERATURE (°C)
9
SHUTDOWN CURRENT (µA)
0
20
-60
-20
VDD = 3.3V
-3
0
-1
40
-2
2
1
0
20
-1
450
400
-20
0
500
4
3
-40
MESUREMENT ERROR (°C)
1
5
-60
2
-40
MESUREMENT ERROR (°C)
3
Operating IDD
vs. Temperature
-40
Local Temperature
Measurement Error
-2
-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
1-Bit
DAC
Digital Filter
and
Control
Logic
Result
Register
A2/T1
A1
A0
2-Wire
Serial Bus
Interface
Temperature
Setpoint
Register
Temperature
Hysteresis
Register
DATA
State
Machine
and
Digital
Comparator
CLK
Configuration
Register
Thermostat
Output
Pointer
Register
INT
MIC184
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.
Functional Description
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
November 2000
MIC184
Micrel
Inputs
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
MIC184 Slave Address
A2/T1
A1
A0
Binary
Hex
0
0
0
100 1000b
48h
0
0
1
100 1001b
49h
0
1
0
100 1010b
4Ah
0
1
1
100 1011b
4Bh
1
0
0
100 1100b
4Ch
1
0
1
100 1101b
4Dh
1
1
0
100 1110b
4Eh
1
1
1
100 1111b
4Fh
diode
0
0
100 1000b
48h
diode
0
1
100 1001b
49h
diode
1
0
100 1010b
4Ah
diode
1
1
100 1011b
4Bh
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
Command_Byte
Target Register
Binary
Hex
Label
Description
0000 0000b
00h
TEMP
measured temperature result
0000 0001b
01h
CONFIG
configuration register
0000 0010b
02h
T_HYST
temperature hysteresis
0000 0011b
03h
T_SET
overtemperature setpoint
0000 0100b
04h
·
·
·
·
·
·
reserved
do not use
1111 1111b
FFh
Table 2. MIC184 Register Addresses
November 2000
7
MIC184
MIC184
MIC184 Slave Address
Command Byte
Data Byte to MIC184
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
8
ACKNOWLEDGE
ACKNOWLEDGE
MIC184 Slave Address
NOT ACKNOWLEDGE
STOP
High-Order Byte from MIC184 Low-Order Byte from MIC184
Figure 3. WRITE_WORD Protocol
ACKNOWLEDGE
Command Byte
R/W = WRITE
STOP
CLK
START
START
R/W = READ
ACKNOWLEDGE
ACKNOWLEDGE
High-Order Byte from MIC184 Low-Order Byte from MIC184
Figure 4. READ_WORD Protocol
ACKNOWLEDGE
MIC184 Slave Address
ACKNOWLEDGE
CLK
START
ACKNOWLEDGE
Master-to-slave transmission
ACKNOWLEDGE
STOP
Slave-to-master response
NOT ACKNOWLEDGE
Figure 5. RECEIVE_DATA from a 16-Bit Register
R/W = READ
DATA 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
R/W = WRITE
NOT ACKNOWLEDGE
DATA 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
CLK
START
DATA 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
CLK
START
DATA 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
START
DATA 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
STOP
MIC184
Micrel
November 2000
November 2000
9
t/INT
START
ACKNOWLEDGE
Command Byte = 01h = CONFIG
MIC184 Slave Address
Result
Ready
CONFIG Value**
tCONV
New Conversion
in Progress
New Conversion
Begins
NOT ACKNOWLEDGE
STOP
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
to be read from 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.
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 powerup default state can be summarized as follows:
• 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.
Temperature
Raw Binary
Masked Binary
Masked Hex
+125° C
0111 1101 0XXX XXXX
0 1111 1010b
0FAh
+25° C
0001 1001 0XXX XXXX
0 0011 0010b
032h
+0.5° C
0000 0000 1XXX XXXX
0 0000 0001b
001h
0° C
0000 0000 0XXX XXXX
0 0000 0000b
000h
–0.5° C
1111 1111 1XXX XXXX
1 1111 1111b
1FFh
–25° C
1110 0111 0XXX XXXX
1 1100 1110b
1CEh
–40° C
1101 1000 0XXX XXXX
1 1011 0000b
1B0h
–55° C
1100 1001 0XXX XXXX
1 1001 0010b
192h
Table 3. Digital Temperature Format
MIC184
10
November 2000
MIC184
Micrel
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
condition, 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
Shutdown Mode
Setting the SHDN bit in the configuration register halts the
otherwise continuous conversions by the A/D converter. The
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
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
CONFIG[4:3]
Fault_Queue Depth
00
1 conversion*
01
2 conversions
10
4 conversions
11
6 conversions
* Default setting
Table 4. Fault_Queue Depth Settings
November 2000
11
MIC184
MIC184
Micrel
LM75 Compatibility
The MIC184 can be used interchangeably with the LM75 in
existing applications. The MIC184 offers several advantages
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.
servicing interrupts for the host to read the current temperature to confirm that the condition that caused the interrupt still
exists.
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 high-Z state. This meets the requirement of an active-low
interrupt for the SMBus, while making IM available as an INTforcing bit for those applications which employ an active-high
INT output (for example, software fan-control routines).
MIC184
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November 2000
MIC184
Micrel
Register Set and Programmer’s Model
Internal Register Set
Name
Description
Command Byte
Operation
Power-Up Default
TEMP
measured temperature
00 h
9-bit read only
0 0000 0000b
0° C(1)
CONFIG
configuration register
01 h
8-bit read/write
0000 0000b
(2)
T_HYST
hysteresis
02h
9-bit read/write
0 1001 0110b
+75° C
T_SET
temperature setpoint
03 h
9-bit read/write
0 1010 0000b
+80° C
Detailed Register Descriptions
CONFIG (8-Bit Read/Write)
D[7]
D[6]
D[5]
read only
read/write
read/write
interrupt
status
(STS)
interrupt
mask(3)
(IM)
temp
select
(ZONE)
D[4]
D[3]
D[2]
D[1]
D[0]
read/write
read/write
read/write
read/write
fault queue
depth
(F_Q)
int
polarity
(POL)
CMP/INT
mode
(MODE)
Shutdown
(SHDN)
Bits
Function
STS
interrupt status (read only)
1 = interrupt occured, 0 = none
interrupt mask
0 = enabled, 1 = disabled
internal/remote temperature selection
1 = remote, 0 = internal
F_Q
Fault_Queue depth
00 = 1 conversion, 01 = 2 conversions,
10 = 4 conversions, 11 = 6 conversions
POL
INT output polarity selection
1 = active high, 0 = active low
MODE
comparator/interrupt
mode selection for INT pin
1 = interrupt mode,
0 = comparator mode
SHDN
normal/shutdown
operating mode selection
1 = shutdown,
0 = normal
IM
ZONE
Operation
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
November 2000
(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
TEMP (9-Bit Read Only)
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]
MSB
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
LSB
X
X
X
X
X
X
X
temperature data from ADC
Bits
Function
D[15:7]
Operation
measured temperature data
for selected zone
read 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_HYST (9-Bit Read/Write)
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]
MSB
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
LSB
X
X
X
X
X
X
X
temperature hysteresis setting
Bits
Function
D[15:7]
Operation
temperature hysteresis setting
read/write*
* 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.
T_HYST Power-Up Default Value: 0 1001 0110b (+75°C)
T_HYST Command Byte Address: 0000 0010b = 02h
Temperature Setpoint Register
T_SET (9-Bit Read/Write)
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]
MSB
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
LSB
X
X
X
X
X
X
X
overtemperature setpoint
Bits
D[15:7]
Function
Operation
overtemperature comparator setpoint
* 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.
T_SET Power-Up Default Value: 0 1010 0000b (+80°C)
T_SET Command Byte Address: 0000 0011b = 03h
MIC184
read/write*
14
November 2000
MIC184
Micrel
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 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.
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}
Applications Information
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.
November 2000
15
MIC184
MIC184
Micrel
{START Polling-Based Test and Initialization
Routine}
1. Temporarily disable the host’s interrupt input
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.
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 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 interruptmode:
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)
∆TJ = 1.11mW × 206°C/W
∆TJ 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
∆VCB-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
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
November 2000
MIC184
Micrel
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 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
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.
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 ∆VBE, 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
November 2000
17
MIC184
MIC184
Micrel
VDD 8
1 DATA
2 CLK
A0 7
3 INT
A1 6
GUARD/RETURN
REMOTE DIODE (A2/T1)
A2/T1 5
4 GND
GUARD/RETURN
Figure 8. Guard Traces/Kelvin Ground Returns
3.0V to 3.6V
100
0.1µF
10k Pull-ups
8
1
FROM
SERIAL BUS
HOST
2
3
MIC184
VDD
A2/T1
DATA
A1
CLK
A0
INT
GND
4.7µF
5
6
2200pF
7
2N3906
4
Figure 9. VDD Decoupling for Very Noisy Supplies
MIC184
18
November 2000
MIC184
Micrel
Package Information
0.026 (0.65)
MAX)
PIN 1
0.157 (3.99)
0.150 (3.81)
DIMENSIONS:
INCHES (MM)
0.020 (0.51)
0.013 (0.33)
0.050 (1.27)
TYP
0.064 (1.63)
0.045 (1.14)
45°
0.0098 (0.249)
0.0040 (0.102)
0.197 (5.0)
0.189 (4.8)
0°–8°
0.010 (0.25)
0.007 (0.18)
0.050 (1.27)
0.016 (0.40)
SEATING
PLANE
0.244 (6.20)
0.228 (5.79)
8-Lead SOP (M)
0.122 (3.10)
0.112 (2.84)
0.199 (5.05)
0.187 (4.74)
DIMENSIONS:
INCH (MM)
0.120 (3.05)
0.116 (2.95)
0.036 (0.90)
0.032 (0.81)
0.043 (1.09)
0.038 (0.97)
0.012 (0.30) R
0.012 (0.03)
0.0256 (0.65) TYP
0.008 (0.20)
0.004 (0.10)
5° MAX
0° MIN
0.007 (0.18)
0.005 (0.13)
0.012 (0.03) R
0.039 (0.99)
0.035 (0.89)
0.021 (0.53)
8-Lead MSOP (MM)
November 2000
19
MIC184
MIC184
MIC184
Micrel
20
November 2000
MIC184
Micrel
MICREL INC. 1849 FORTUNE DRIVE SAN JOSE, CA 95131
TEL
+ 1 (408) 944-0800
FAX
+ 1 (408) 944-0970
WEB
USA
http://www.micrel.com
This information is believed to be accurate and reliable, however no responsibility is assumed by Micrel for its use nor for any infringement of patents or
other rights of third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent right of Micrel Inc.
© 2000 Micrel Incorporated
November 2000
21
MIC184