MICREL MIC284-0BM

MIC284
Micrel
MIC284
Two-Zone Thermal Supervisor
Advance Information
General Description
Features
The MIC284 is a versatile digital thermal supervisor capable
of measuring temperature using its own internal sensor and
an inexpensive external sensor or embedded silicon diode
such as those found in the Intel Pentium III* CPU. A 2-wire
serial interface is provided to allow communication with either
I2C** or SMBus* masters. Features include an open-drain
over-temperature output with dedicated registers for implementing fan control or over-temperature shutdown circuits.
Interrupt status and mask bits are provided for reduced
software overhead. The open-drain interrupt output pin can
be used as either an overtemperature alarm or a thermostatic
control signal. A programmable address pin permits two
devices to share the bus. (Alternate base addresses available-contact Micrel.) Superior performance, low power and
small size makes the MIC284 an excellent choice for the most
demanding thermal management applications.
• Optimized for CPU Thermal Supervision in Computing
Applications
• Measures Local and Remote Temperature
• Sigma-Delta ADC for 8-Bit Temperature Results
• 2-Wire SMBus-compatible Interface
• Programmable Thermostat Settings for both Internal and
External Zones
• Open-Drain Interrupt Output Pin
• Open-Drain Over Temperature Output Pin for Fan
Control or Hardware Shutdown
• Interrupt Mask and Status Bits
• Low Power Shutdown Mode
• Failsafe response to diode faults
• 2.7V to 5.5V Power Supply Range
• 8-Lead SOIC and MSOP Packages
*SMBus and Pentium III are trademarks of Intel Corporation.
•
•
•
•
•
Applications
**I2C is a trademark of Philips Electronics, N.V.
Ordering Information
Desktop, Server and Notebook Computers
Power Supplies
Test and Measurement Equipment
Wireless Systems
Networking/Datacom Hardware
Part Number
Base Address(*)
Junction Temp. Range
Package
MIC284-0BM
100 100x
–55°C to +125°C
8-Lead SOP
MIC284-1BM
100 101x
–55°C to +125°C
8-Lead SOP
Contact Factory
MIC284-2BM
100 110x
–55°C to +125°C
8-Lead SOP
Contact Factory
MIC284-3BM
100 111x
–55°C to +125°C
8-Lead SOP
Contact Factory
MIC284-0BMM
100 100x
–55°C to +125°C
8-Lead MSOP
MIC284-1BMM
100 101x
–55°C to +125°C
8-Lead MSOP
Contact Factory
MIC284-2BMM
100 110x
–55°C to +125°C
8-Lead MSOP
Contact Factory
MIC284-3BMM
100 111x
–55°C to +125°C
8-Lead MSOP
Contact Factory
Notes
* The least-significant bit of the slave address is determined by the state of the A0 pin.
Typical Application
3.3V
4 × 10k
pull-ups
FROM
SERIAL BUS
HOST
OVER-TEMP
SHUTDOWN
0.1µF
MIC284
DATA
VDD
CLK
T1
/INT
/CRIT
REMOTE
DIODE
A0
GND
2200pF
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
September 29, 2000
1
MIC284
MIC284
Micrel
Pin Configuration
DATA 1
8 VDD
CLK 2
7 A0
/INT 3
6 T1
GND 4
5 /CRIT
Pin Description
Pin Number
Pin Name
1
DATA
2
CLK
Digital Input: The host provides the serial bit clock on this input.
3
/INT
Digital Output: Open-drain. Interrupt or thermostat output.
4
GND
Ground: Power and signal return for all IC functions.
5
/CRIT
Digital Output: Open-Drain. Over-temperature indication
6
T1
Analog Input: Connection to remote temperature sensor (diode junction)
7
A0
Digital Input: Slave address selection input. See Table 1. MIC284 Slave
Address Settings.
8
VDD
MIC284
Pin Function
Digital I/O: Open-drain. Serial data input/output.
Analog Input: Power supply input to the IC.
2
September 29, 2000
MIC284
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 ................................................ ±10 mA
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
Min
Supply Current
/INT, open, A0 = VDD or GND,
CLK = DATA = high, normal mode
Typ
Max
Units
350
750
µA
Power Supply
IDD
/INT, /CRIT open, A0 = VDD or GND
shutdown mode, CLK = 100kHz
3
/INT, /CRIT open, A0 = VDD or GND
shutdown mode, CLK = DATA = high
1
tPOR
Power-On Reset Time, Note 7
VDD > VPOR
VPOR
Power-On Reset Voltage
all registers reset to default values,
A/D conversions initiated
VHYST
Power-On Reset Hysteresis Voltage
2.0
µA
10
µA
200
µs
2.7
V
250
mV
Temperature-to-Digital Converter Characteristics
Accuracy—Local Temperature
Note 4, 9
Accuracy—Remote Temperature
Note 4, 5, 9
tCONV0
Conversion Time, local zone
Note 7
tCONV1
Conversion Time, remote zone
Note 7
0°C ≤ TA ≤ +100°C, /INT and /CRIT open,
3V ≤ VDD ≤ 3.6V
±1
±2
°C
–55°C ≤ TA ≤ +125°C, /INT and /CRIT open,
3V ≤ VDD ≤ 3.6V
±2
±3
°C
0°C ≤ TD ≤ +100°C, /INT and /CRIT open,
3V ≤ VDD ≤ 3.6V, 0°C ≤ TA ≤ +85°C
±1
±3
°C
–55°C ≤ TD ≤ +125°C, /INT and /CRIT open,
3V ≤ VDD ≤ 3.6V, 0°C ≤ TA ≤ +85°C
±2
±5
°C
50
80
ms
100
160
ms
224
400
µA
Remote Temperature Input (T1)
IF
Current to External Diode
Note 7
high level, T1 forced to 1.5V
low level
7.5
µA
14
Address Input (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
September 29, 2000
0.6
2.0
V
10
±0.01
3
V
pF
±1
µA
MIC284
MIC284
Symbol
Micrel
Parameter
Condition
Min
Typ
Max
Units
Serial Data I/O Pin (DATA)
VOL
Low Output Voltage
IOL = 3mA
0.4
V
Note 6
IOL = 6mA
0.8
V
VIL
Low Input Voltage
2.7V ≤ VDD ≤ 5.5V
0.3VDD
V
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 6
tINT
Interrupt Propagation Delay,
Note 7, 8
from TEMP > T_SET or TEMPx < T_HYSTx
to INT < VOL, FQ = 00, RPULLUP = 10kΩ
tnINT
Interrupt Reset Propagation Delay,
Note 7
from any register read to /INT > VOH
FQ = 00, RPULLUP = 10kΩ
T_SET0
Default T_SET0 Value
tPOR after VDD > VPOR
81
81
81
°C
T_HYST0
Default T_HYST0 Value
tPOR after VDD > VPOR
76
76
76
°C
T_SET1
Default T_SET1 Value
tPOR after VDD > VPOR
97
97
97
°C
T_HYST1
Default T_HYST1 Value
tPOR after VDD > VPOR
92
92
92
°C
IOL = 3mA
0.4
V
IOL = 6mA
0.8
V
tCONV+1
µs
1
µs
Over-Temperature Output (/CRIT)
VOL
Low Output Voltage,
Note 6
tCRIT
/CRIT Propagation Delay,
Note 7, 8
from TEMPx > T_SETx or TEMPx < T_HYSTx
to INT < VOL, FQ = 00, RPULLUP = 10kΩ
tnCRIT
/CRIT Reset Propagation Delay,
Note 7
from TEMPx < nCRITx to /CRIT > VOH
FQ = 00, RPULLUP = 10kΩ
CRIT1
Default CRIT1 Value
tPOR after VDD > VPOR
97
97
97
°C
nCRIT1
Default nCRIT1 Value
tPOR after VDD > VPOR
92
92
92
°C
Serial Interface Timing (Note 7)
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
MIC284
4
September 29, 2000
MIC284
Micrel
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.
TD is the temperature of the remote diode junction. Testing is performed using a single unit of one of the transistors listed in Table 6.
Note 6.
Current into this pin will result in self-heating of the MIC284. Sink current should be minimized for best accuracy.
Note 7.
Guaranteed by design over the operating temperature range. Not 100% production tested.
Note 8.
tCONV = tCONV0 + tCONV1. tCONV0 is the conversion time for the local zone; tCONV1 is the conversion time for the remote zone.`
Note 9.
Accuracy specification does not include quantization noise, which may be as great as ±1⁄ 2LSB (±0.5°C).
Timing Diagram
t1
SCL
t4
t2
t5
SDA Data In
t3
SDA Data Out
Serial Interface Timing
September 29, 2000
5
MIC284
MIC284
Micrel
Functional Diagram
VDD
TEMPERATURE-TO-DIGITAL
CONVERTER
T1
∫
2:1
MUX
∑
Bandgap
Sensor
and
Reference
1-Bit
DAC
Digital Filter
and
Control
Logic
Result
Registers
A0
2-Wire
Serial Bus
Interface
T_SET & /CRIT
Setpoint
Registers
State
Machine
and
Digital
Comparator
Temperature
Hysteresis
Registers
DATA
Pointer
Register
CLK
Configuration
Register
Open-Drain
Output
/INT
/CRIT
MIC284
GND
and Power On" for more information. A0 determines the slave
address as shown in Table 1:
FUNCTIONAL DESCRIPTION
Pin Descriptions
VDD: Power supply input. See electrical specifications.
GND: Ground return for all MIC284 functions.
CLK: Clock input to the MIC284 from the two-wire serial bus.
The clock signal is provided by the host, and is shared by all
devices on the bus.
DATA: Serial data I/O pin that connects to the two-wire serial
bus. DATA is bi-directional 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.
A0: This inputs sets the least significant bit of the MIC284’s
7-bit slave address. The six most-significant bits are fixed
and are determined by the part number ordered. (See ordering information table above.) Each MIC284 will only respond
to its own unique slave address, allowing up to eight MIC284s
to share a single bus. A match between the MIC284’s
address and the address specified in the serial bit stream
must be made to initiate communication. A0 should be tied
directly to VDD or ground. See "Temperature Measurement
MIC284
Part Number
Inputs
MIC284 Slave Address
A0
Binary
Hex
0
100 1000b
48h
1
100 1001b
49h
MIC284-1
0
100 1010b
4Ah
1
100 1011b
4Bh
MIC284-2
0
100 1100b
4Ch
1
100 1101b
4Dh
0
100 1110b
4Eh
1
100 1111b
4Fh
MIC284-0
MIC284-3
Table 1. MIC284 Slave Address Settings
/INT: Temperature events are indicated to external circuitry
via this output. Operation of the /INT output is controlled by
the MODE and IM bits in the MIC284’s configuration register.
See "Comparator and Interrupt Modes" below. This output is
open-drain and may be wire-OR’ed 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
6
September 29, 2000
MIC284
Micrel
set, it prevents the /INT output from sinking current. In I2C
and SMBus systems, the IM bit is therefore an interrupt mask
bit.
/CRIT: Over-temperature events are indicated to external
circuitry via this output. This output is open-drain and may be
wire-OR’ed with other open-drain signals. Most systems will
require a pull-up resistor or current source on this pin.
T1: This pin connects to an off-chip PN diode junction, for
monitoring the junction temperature at a remote location. The
remote diode may be an embedded thermal sensing junction
in an integrated circuit so equipped (such as Intel's Pentium
III), or a discrete 2N3906-type bipolar transistor with base and
collector tied together.
Temperature Measurement
The temperature-to-digital converter is built around a switched
current source and an eight-bit analog-to-digital converter.
Each diode's temperature is calculated by measuring its
forward voltage drop at two different current levels. An
internal multiplexer directs the MIC284's current source output to either an internal or external diode junction. The
MIC284 uses two’s-complement data to represent temperatures. If the MSB of a temperature value is zero, the
temperature is zero or positive. If the MSB is one, the
temperature is negative. More detail on this is given in the
"Temperature Data Format" section below. A “temperature
event” results if the value in either of the temperature result
registers (TEMPx) becomes greater than the value in the
corresponding temperature setpoint register (T_SETx). Another temperature event occurs if and when the measured
temperature subsequently falls below the temperature hysteresis setting in T_HYSTx.
During normal operation the MIC284 continuously performs
temperature-to-digital conversions, compares the results
against the setpoint registers, and updates the states of /INT,
/CRIT, and the status bits accordingly. The remote zone is
converted first, followed by the local zone. The states of /INT,
/CRIT, and the status bits are updated after each measurement is taken. The remote diode junction connected to T1
may be embedded in an integrated circuit such as a CPU,
ASIC, or graphics processor, or it may be a diode-connected
discrete transistor.
September 29, 2000
Diode Faults
The MIC284 is designed to respond in a failsafe manner to
hardware faults in the external sensing circuitry. If the
connection to the external diode is lost or the sense line (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°C). This will cause a temperature event to occur if
T_SET1 or CRIT1 are set to any value less than 127°C (7Fh
= 0111 1111b). An interrupt will be generated on /INT if so
enabled. The temperature reported for the external zone will
remain +127°C until the fault condition is cleared. This fault
detection mechanism requires that the MIC284 complete the
number of conversion cycles specified by Fault_Queue. The
part will 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 MIC284 uses standard SMBus Write_Byte and
Read_Byte operations for communication with its host. The
SMBus Write_Byte operation involves sending the device’s
slave address (with the R/W bit low to signal a write operation), followed by a command byte and a data byte. 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 MIC284,
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
the part may then be clocked out.
The command byte is eight bits wide. This byte carries the
address of the MIC284 register to be operated upon, and is
stored in the part’s pointer register. The pointer register is an
internal write-only register. The command byte (pointer
register) values corresponding to the various MIC284 register addresses are shown in Table 2. Command byte values
other than those explicitly shown are reserved, and should
not be used. Any command byte sent to the MIC284 will
persist in the pointer register indefinitely until it is overwritten
by another command byte. If the location latched in the
pointer register from the last operation is known to be correct
(i.e., points to the desired register), then the Receive_Byte
procedure may be used. To perform a Receive_Byte, the host
sends an address byte to select the MIC284, and then
retrieves the data byte. Figures 1 through 3 show the formats
for these procedures.
7
MIC284
MIC284
Micrel
Command_Byte
Binary
Hex
Target Register
Label
Description
0000 0000b
00h
TEMP0
local temperature
0000 0001b
01h
CONFIG
configuration register
0000 0010b
02h
T_HYST0
local temperature hysteresis
0000 0011b
03h
T_SET0
local temperature setpoint
0001 0000b
10h
TEMP1
remote temperature
0001 0010b
12h
0001 0011b
13h
T_SET1
remote temperature setpoint
0010 0010b
22h
nCRIT1
over-temperature hysteresis
0010 0011b
23h
CRIT1
over-temperature setpoint
T_HYST1 remote temperature hysteresis
Table 2. MIC284 Register Addresses
MIC284
8
September 29, 2000
September 29, 2000
Command Byte
Data Byte to MIC284
START
ACKNOWLEDGE
Master-to-slave transmission
ACKNOWLEDGE
Command Byte
NOT ACKNOWLEDGE
STOP
Data Read From MIC284
Slave-to-master response
MIC284 Slave Address
Figure 1. WRITE_BYTE Protocol
R/W = WRITE
CLK
START
9
ACKNOWLEDGE
R/W = READ
MIC284 Slave Address
Data Byte from MIC284
CLK
R/W = READ
NOT ACKNOWLEDGE
Slave-to-master response
ACKNOWLEDGE
Figure 3. RECEIVE_BYTE
Master-to-slave transmission
START
STOP
NOT ACKNOWLEDGE
STOP
Slave-to-master response
ACKNOWLEDGE
Master-to-slave transmission
START
Figure 2. READ_BYTE Protocol
ACKNOWLEDGE
DATA S 1 0 0 1 X X A0 1 A X X X X X X X X /A P
R/W = WRITE
DATA S 1 0 0 1 X X A0 0 A 0 0 X X X X X X A S 1 0 0 1 X X A0 1 A X X X X X X X X /A P
MIC284 Slave Address
CLK
DATA S 1 0 0 1 X X A0 0 A 0 0 X X X X X X A X X X X X X X X /A P
MIC284 Slave Address
MIC284
Micrel
MIC284
MIC284
10
START
ACKNOWLEDGE
Command Byte = 01h = CONFIG
MIC284 Slave Address
Figure 4. A/D Converter Timing
Slave-to-master response
First
Result
Ready
CONFIG Value*
tCONV1
New Conversion
in Progress
New Conversion
Begins
NOT ACKNOWLEDGE
STOP
START
ACKNOWLEDGE
ACKNOWLEDGE
tn/INT
R/W = READ
ACKNOWLEDGE
Master-to-slave transmission
START
Figure 5. Responding to Interrupts
* Status bits in CONFIG are cleared to zero following this operation
R/W = WRITE
Slave-to-master response
NOT ACKNOWLEDGE
S 1 0 0 0 X X A0 0 A 0 0 0 0 0 0 0 1 A S 1 0 0 0 X X A0 1 A X X X X X X X X /A P
MIC284 Slave Address
Last Byte of Transaction
X X X X X X X X /A P
A/D Converter
in Standby
ACKNOWLEDGE
…
Master-to-slave transmission
Conversion Interrupted
By MIC284 Acknowledge
Conversion
in Progress
R/W = DONT CARE
Temperature event occurs
INT
t/INT
First Byte of Transaction
S 1 0 0 1 X X X X A X X X X X X X X A
MIC284 Slave Address
STOP
MIC284
Micrel
September 29, 2000
MIC284
Micrel
Temperature Data Format
The LSB of each register represents one degree Centigrade.
The values are in a two’s complement format, wherein the
most significant bit (D7), represents the sign: zero for positive
temperatures and one for negative temperatures. Table 3
shows examples of the data format used by the MIC284 for
temperatures.
A/D Converter Timing
Whenever the MIC284 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 MIC284. When the part is accessed, the
conversion in progress will be halted, and the partial result
discarded. When the access to the MIC284 is complete, the
ADC will begin a new conversion cycle with results for the
remote zone valid tCONV1 after that, and for the local zone
tCONV0 later. Figure 4 shows this behavior. The conversion
time is twice as long for external conversions as it is for
internal conversions. This allows the use of a filter capacitor
on T1 without a loss of accuracy due to the resulting longer
settling times.
Upon powering-up, coming out of shutdown mode, or resuming operation following a serial bus transaction, the ADC will
begin acquiring temperature data starting with the external
zone (zone 1), followed by the internal zone (zone 0). If the
ADC is interrupted by a serial bus transaction, it will restart the
conversion that was interrupted and then continue in the
normal sequence. This sequence will repeat indefinitely until
the MIC284 is shut down, powered off, or is interrupted by a
serial bus transaction as described above.
Power-On
When power is initially applied, the MIC284’s internal registers are set to their default states, and A0 is read to establish
the device’s slave address. The MIC284’s power-up default
state can be summarized as follows:
• Normal Mode operation (i.e., part is not in shutdown)
• /INT function is set to Comparator Mode
• Fault Queue depth = 1 (FQ=00)
• Interrupts are enabled (IM = 0)
• T_SET0 = 81°C; T_HYST0 = 76°C
• T_SET1 = 97°C; T_HYST1 = 92°C
• CRIT1 = 97°C; nCRIT1 = 92°C
• Initialized to recognize overtemperature faults
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 when the measured temperature, as reported in
either of the TEMPx registers, exceeds the threshold programmed into the corresponding T_SETx register for the
number of conversions specified by Fault_Queue (described
below). In comparator mode, /INT will remain asserted and
the status bits will remain high unless and until the measured
temperature falls below the value in the T_HYSTx 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 a
status bit (Sx) to be set, and the /INT output to be asserted,
they will not be automatically de-asserted when the measured temperature falls below T_HYSTx. They can only be
de-asserted by reading any of the MIC284’s internal registers
or by putting the device into shutdown mode. If the most
recent temperature event was an overtemperature condition,
Sx will not be set again, and /INT cannot be reasserted, until
the device has detected that TEMPx < T_HYSTx. Similarly,
if the most recent temperature event was an undertemperature
condition, Sx will not be set again, and /INT cannot be
reasserted, until the device has detected that TEMPx >
T_SETx. This keeps the internal logic of the MIC284 backward compatible with that of the LM75 and similar devices. In
both modes, the MIC284 will be responsive to over-temperature events at power-up. See "Interrupt Generation", below.
Shutdown Mode
Setting the SHDN bit in the configuration register halts the
otherwise continuous conversions by the A/D converter. The
MIC284’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
part’s power consumption.
Entering shutdown mode will not affect the state of /INT when
the device is in comparator mode (MODE = 0). It will retain
its state until after the device exits shutdown mode and
resumes A/D conversions.
Temperature
Binary
Hex
+125° C
0111 1101b
7Dh
+25° C
0001 1001b
19h
+1.0° C
0000 0001b
01h
0° C
0000 0000b
00h
– 1.0° C
1111 1111b
FFh
– 25° C
1110 0111b
E7h
– 40° C
1101 1000b
D8h
– 55° C
1100 1001b
C9h
Table 3. Digital Temperature Format
September 29, 2000
11
MIC284
MIC284
Micrel
If the device is shut down while in interrupt mode (mode = 1),
the /INT pin will be unconditionally de-asserted and the
internal latches holding the interrupt status will be cleared.
Therefore, no interrupts will be generated while the MIC284
is in shutdown mode, and the interrupt status will not be
retained. Regardless of the setting of the MODE bit, the state
of /CRIT and its corresponding status bit, CRIT1, does not
change when the MIC284 enters shutdown mode. They will
retain their states until after the device exits shutdown mode
and resumes A/D conversions. Since entering shutdown
mode stops A/D conversions, the MIC284 is incapable of
detecting or reporting temperature events of any kind while in
shutdown. Diode fault detection requires one or more A/D
conversion cycles to detect external sensor faults, therefore
diode faults will not be reported until the MIC284 exits
shutdown (see "Diode Faults" above).
Fault Queues
Fault queues (programmable digital filters) are provided in
the MIC284 to prevent false tripping due to thermal or
electrical noise. The two bits in CONFIG[4:3] set the depth of
Fault_Queue. Fault_Queue then determines the number of
consecutive temperature events (TEMPx > T_SETx, TEMPx
< T_HYSTx, TEMP1 > CRIT1, or TEMP1 < nCRIT1) which
must occur in order for the condition to be considered valid.
There are separate fault queues for each zone and for the
over-temperature detect function. As an example, assume
the part is in comparator mode, and CONFIG[4:3] is programmed with 10b. The measured temperature in zone one
would have to exceed T_SET1 for four consecutive A/D
conversions before /INT would be asserted or the S1 status
bit set. Similarly, TEMP1 would have to be less than T_HYST1
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 x tCONV to detect a temperature event.
The depth of Fault_Queue vs. D[4:3] of the configuration
register is shown in Table 4:
CONFIG[4:3]
Fault_Queue Depth
00
1 conversion*
01
2 conversions
10
4 conversions
11
6 conversions
should read the contents of the configuration register to
confirm that the MIC284 was the source of the interrupt. A
read operation on any register will cause /INT to be deasserted. This is shown in Figure 5. The status bits will be
cleared once CONFIG has been read.
Since temperature-to-digital conversions continue while /INT
is asserted, the measured temperature could change between the MIC284’s assertion of /INT or /CRIT and the host’s
response. It is good practice for the interrupt service routine
to read the value in TEMPx, to verify that the over-temperature or under-temperature condition still exists. In addition,
more than one temperature event may have occurred simultaneously or in rapid succession between the assertion of
/INT and servicing of the MIC284 by the host. The interrupt
service routine should allow for this eventuality. Keep in mind
that clearing the status bits and deasserting /INT is not
sufficient to allow further interrupts to occur. TEMPx must
become less than T_HYSTx if the last event was an overtemperature condition, or greater than T_SETx if the last
event was an under-temperature condition, before /INT can
be asserted again.
Putting the device into shutdown mode will de-assert /INT
and clear the S0 and S1 status bits. This should not be done
before completing the appropriate interrupt service routine(s).
/CRIT Output
If and when the measured remote temperature exceeds the
value programmed into the CRIT1 register, the /CRIT output
will be asserted and CRIT1 in the configuration register will be
set. If and when the measured temperature in zone one
subsequently falls below the value programmed into nCRIT1,
the /CRIT output will be de-asserted and the CRIT1 bit in
CONFIG will be cleared. This action cannot be masked and
is completely independent of the settings of the mode bit and
interrupt mask bit. The host may poll the state of the /CRIT
output at any time by reading the configuration register. The
state of the CRIT1 bit exactly follows the state of the /CRIT
output. The states of /CRIT and CRIT1 do not change when
the MIC284 enters shutdown mode. Entering shutdown mode
stops A/D conversions, however, so their states will not
change while the device is shut down.
Polling
The MIC284 may either be 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 bits. The act of reading
CONFIG clears the status bits. If more than one event that
sets a given status bit occurs before the host polls the
MIC284, only the fact that at least one such event has
occurred will be apparent to the host. For polled systems, the
interrupt mask bit should be set (IM = 1). This will disable
interrupts from the MIC284, and prevent the /INT pin from
sinking current. The host may poll the state of the /CRIT
output at any time by reading the configuration register. The
state of the CRIT1 bit exactly follows the state of the /CRIT
output.
* Default setting
Table 4. Fault_Queue Depth Settings
Interrupt Generation
Assuming the MIC284 is in interrupt mode and interrupts are
enabled, there are five different conditions that will cause the
MIC284 to set one of the status bits (S0, S1, or CRIT1) in
CONFIG and assert the /INT output and/or the /CRIT output.
These conditions are listed in Table 5. When a temperature
event occurs, the corresponding status bit will be set in
CONFIG. This action cannot be masked. However, a
temperature event will only generate an interrupt signal on /
INT if it is specifically enabled by the interrupt mask bit (IM =0
in the configuration register). Following an interrupt, the host
MIC284
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September 29, 2000
MIC284
Micrel
EVENT
CONDITION*
MIC284 Response**
High temperature, remote
TEMP1 > T_SET1
Set S1 in CONFIG, assert /INT
High temperature, local
TEMP0 > T_SET0
Set S0 in CONFIG, assert /INT
Low temperature, remote
TEMP1 < T_HYST1
Set S1 in CONFIG, assert /INT
Low temperature, local
TEMP0 < T_HYST0
Set S0 in CONFIG, assert /INT
Over-temperature, remote
TEMP1 > CRIT1
Set CRIT in CONFIG, assert /CRIT
NOT Over-temperature, remote
TEMP < nCRIT1
Clear CRIT in CONFIG, de-assert /CRIT
Diode Fault
T1 open or T1 shorted to VDD or GND
Set CRIT and S1 in CONFIG, assert /INT
and /CRIT***
*
CONDITION must be true for Fault_Queue conversions to be recognized
** Assumes interupts enabled
*** Assumes that T_SET1 and CRIT1 are set to any value less than +127° C = 7Fh = 0111 1111b.
Table 5. MIC284 Temperature Events
September 29, 2000
13
MIC284
MIC284
Micrel
Register Set and Programmer’s Model
Internal Register Set
Name
Description
Command Byte
Operation
Power-Up Default
TEMP0
local temperature
00h
8-bit read only
00h (0° C)(1)
CONFIG
configuration register
01h
8-bit read/write
00h (2)
T_HYST0
local hysteresis
02h
8-bit read/write
4Ch (+76° C)
T_SET0
local temperature setpoint
03 h
8-bit read/write
51h (+81° C)
TEMP1
remote temperature
10h
8-bit read only
00h (0° C)(1)
T_HYST1
remote hysteresis
12 h
8-bit read/write
5Ch (+92° C)
T_SET1
remote temperature
setpoint
13h
8-bit read/write
61h (+97° C)
nCRIT1
over-temperature
hysteresis
22h
8-bit read/write
5Ch (+92° C)
CRIT1
over-temperature
temperature setpoint
23 h
8-bit read/write
61h (+97° C)
(1)
TEMP0 and TEMP1 will contain measured temperature data after the completion of one conversion cycle.
(2)
After the first Fault_Queue conversions are complete, status bits will be set if TEMPx > T_SETx or TEMP1 > CRIT1.
Detailed Register Descriptions
Configuration Register
CONFIGURATION REGISTER (CONFIG)
8-Bit Read/Write
D[7]
D[6]
D[5]
read only
read only
read only
local
status
(S0)
remote
status
(S1)
/CRIT
status
(CRIT1)
Bits
D[4]
D[3]
D[2]
D[1]
D[0]
read/write
read/write
read/write
read/write
fault queue
depth
(FQ[1:0])
interrupt
mask
(IM)
CMP/INT
mode
(MODE)
Shutdown
(SHDN)
Function
Operation
S0
local interrupt status (read only)
1 = event occured, 0 = no event
S1
remote interrupt status (read only)
1 = event occured, 0 = no event
CRIT1 remote over-temperature status (read only)
1 = over-temperature, 0 = no event
FQ[1:0] Fault_Queue depth
00 = 1 conversion, 01 = 2 conversions,
10 = 4 conversions, 11 = 6 conversions
IM
interrupt mask
1 = disabled, 0 = interrupts enabled
comparator/interrupt
MODE
mode selection for /INT pin
SHDN
1 = interrupt mode,
0 = comparator mode
normal/shutdown
operating mode selection
1 = shutdown,
0 = normal
CONFIG Power-Up Value: 0000 0000b = 00h(*)
• not in shutdown mode
• comparator mode
• /INT = active low
• Fault_Queue depth = 1
• interrupts enabled.
• no temperature events pending
CONFIG Command Byte Value: 0000 0001b = 01h
* Following the first Fault_Queue conversions, one or more of the status bits may be set.
MIC284
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September 29, 2000
MIC284
Micrel
Local Temperature Result Register
LOCAL TEMPERATURE RESULTS (TEMP0)
8-Bit Read Only
D[7]
D[6]
D[5]
D[4]
D[3]
D[2]
D[1]
D[0]
MSB
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
LSB
local temperature data from ADC*
Bits
D[7:0]
Function
Operation
measured temperature data for the local
zone*
TEMP0 Power-Up Value: 0000 0000b = 00h (0°C)†
TEMP0 Command Byte Value: 0000 0000b = 00h
read only
* Each LSB represents one degree Centigrade. The values are
in a two's complement format such that 0°C is reported as
0000 0000b. See "Temperature Data Format" for more details.
†
TEMP0 will contain measured temperature data after the
completion of one conversion.
Local Temperature Hysteresis Register
LOCAL TEMPERATURE HYSTERESIS (T_HYST0)
8-Bit Read/Write
D[7]
D[6]
D[5]
D[4]
D[3]
D[2]
D[1]
D[0]
MSB
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
LSB
local temperature hysteresis setting
Bits
D[7:0]
Function
Operation
local temperature hysteresis setting*
read/write
* Each LSB represents one degree Centigrade. The values are
in a two's complement format such that 0°C is reported as
0000 0000b. See "Temperature Data Format" for more details.
T_HYST0 Power-Up Value: 0100 1100b = 4Ch (+76°C)
T_HYST0 Command Byte Value: 0000 0010b = 02h
Local Temperature Setpoint Register
LOCAL TEMPERATURE SETPOINT (T_SET0)
8-Bit Read/Write
D[7]
D[6]
D[5]
D[4]
D[3]
D[2]
D[1]
D[0]
MSB
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
LSB
local temperature setpoint
Bits
D[7:0]
Function
Operation
local temperature setpoint*
read/write
* Each LSB represents one degree Centigrade. The values are
in a two's complement format such that 0°C is reported as
0000 0000b. See "Temperature Data Format" for more details.
T_SET0 Power-Up Value: 0101 0001b = 51h (+81°C)
T_SET0 Command Byte Value: 0000 0011b = 03h
September 29, 2000
15
MIC284
MIC284
Micrel
Remote Temperature Result Register
REMOTE TEMPERATURE RESULT (TEMP1)
8-Bit Read Only
D[7]
D[6]
D[5]
D[4]
D[3]
D[2]
D[1]
D[0]
MSB
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
LSB
remote temperature data from ADC*
Bits
D[7:0]
Function
Operation
measured temperature data for the remote
read only
zone*
TEMP1 Power-Up Value: 0000 0000b = 00h (0°C)†
TEMP1 Command Byte Value: 0001 0000b = 10h
* Each LSB represents one degree Centigrade. The values are
in a two's complement format such that 0°C is reported as
0000 0000b. See "Temperature Data Format" for more details.
†
TEMP1 will contain measured temperature data for the
selected zone after the completion of one conversion.
Remote Temperature Hysteresis Register
REMOTE TEMPERATURE HYSTERESIS (T_HYST1)
8-Bit Read/Write
D[7]
D[6]
D[5]
D[4]
D[3]
D[2]
D[1]
D[0]
MSB
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
LSB
remote temperature hysteresis setting
Bits
D[7:0]
Function
Operation
remote temperature hysteresis setting*
read/write
* Each LSB represents one degree Centigrade. The values are
in a two's complement format such that 0°C is reported as
0000 0000b. See "Temperature Data Format" for more details.
T_HYST1 Power-Up Value: 0101 1100b = 5Ch (+92°C)
T_HYST1 Command Byte Value: 0001 0010b = 12h
Remote Temperature Setpoint Register
REMOTE TEMPERATURE SETPOINT (T_SET1)
8-Bit Read/Write
D[7]
D[6]
D[5]
D[4]
D[3]
D[2]
D[1]
D[0]
MSB
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
LSB
remote temperature setpoint
Bits
D[7:0]
Function
Operation
remote temperature setpoint*
read/write
* Each LSB represents one degree Centigrade. The values are
in a two's complement format such that 0°C is reported as
0000 0000b. See "Temperature Data Format" for more details.
T_SET1 Power-Up Value: 0110 0001b = 61h (+97°C)
T_SET1 Command Byte Value: 0001 0011b = 13h
MIC284
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September 29, 2000
MIC284
Micrel
Remote Over-Temperature Hysteresis Register
REMOTE OVER-TEMPERATURE HYSTERESIS (nCRIT1)
8-Bit Read/Write
D[7]
D[6]
D[5]
D[4]
D[3]
D[2]
D[1]
D[0]
MSB
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
LSB
remote over-temperature hysteresis setting
Bits
D[7:0]
Function
Operation
remote temperature hysteresis setting*
read/write
* Each LSB represents one degree Centigrade. The values are
in a two's complement format such that 0°C is reported as
0000 0000b. See "Temperature Data Format" for more details.
nCRIT Power-Up Value: 0101 1100b = 5Ch (+92°C)
nCRIT1 Command Byte Value: 0010 0010b = 22h
Remote Over-Temperature Setpoint Register
REMOTE OVER-TEMPERATURE SETPOINT (CRIT1)
8-Bit Read/Write
D[7]
D[6]
D[5]
D[4]
D[3]
D[2]
D[1]
D[0]
MSB
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
LSB
remote over-temperature setpoint
Bits
D[7:0]
Function
Operation
remote over-temperature setpoint*
read/write
* Each LSB represents one degree Centigrade. The values are
in a two's complement format such that 0°C is reported as
0000 0000b. See "Temperature Data Format" for more details.
CRIT1 Power-Up Value: 0110 0001b = 61h (+97°C)
CRIT1 Command Byte Value: 0010 0011b = 23h
September 29, 2000
17
MIC284
MIC284
Micrel
of the thermal data (e.g., PC board thermal conductivity and
ambient temperature) may be poorly defined or unobtainable
except by empirical means.
Series Resistance
The operation of the MIC284 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 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 MIC284. 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 MIC284’s temperature measurement. It isn’t difficult to
keep the series resistance well below an ohm (typically <
0.1Ω), so this will rarely be an issue.
Filter Capacitor Selection
Applications
Remote Diode Selection
Most small-signal PNP transistors with characteristics similar
to the JEDEC 2N3906 will perform well as remote temperature sensors. Table 6 lists several examples of such parts
that Micrel has tested for use with the MIC284. Other
transistors equivalent to these should also work well.
Minimizing Errors
Self-Heating
One concern when using a part with the temperature accuracy and resolution of the MIC284 is to avoid errors induced
by self-heating (VDD × IDD) + (VOL × IOL). In order to
understand what level of error this might represent, and how
to reduce that error, the dissipation in the MIC284 must be
calculated and its effects reduced to a temperature offset.
The worst-case operating condition for the MIC284 is when
VDD = 5.5V, MSOP-08 package. T he maximum power
dissipated in the part is given in Equation 1 below.
In most applications, the /INT output will be low for at most a
few milliseconds before the host resets it back to the high
state, making its duty cycle low enough that its contribution to
self-heating of the MIC284 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, give a better
system-level view of device self-heating in interrupt-mode
usage. This is illustrated by Equation 2.
If the part is to be used in comparator mode, calculations
similar to those shown in Equation 2 (accounting for the
expected value and duty cycle of IOL(/INT) and IOL(/CRIT))
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
It is sometimes desirable to use a filter capacitor between the
T1 and GND pins of the MIC284. The use of this capacitor is
recommended in environments with a lot of high frequency
noise (such as digital switching noise), or if long wires are
used to attach to the remote diode. The maximum recommended total capacitance from the T1 pin to GND is 2700pF.
This typically 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 MIC284, using twisted pair wiring or shielded
microphone cable for the connections to the diode can
significantly help reduce noise pickup. If using a long run of
shielded cable, remember to subtract the cable’s conductorto-shield capacitance from the 2700pF maximum total capacitance.
PD = [(IDD × VDD ) + (IOL(DATA) × VOL(DATA) ) + (IOL(/INT) × VOL(/INT) ) + (IOL(/CRIT) × VOL(/CRIT) )]
PD = [(0.75mA × 5.5V) + (6mA × 0.8V) + (6mA × 0.8V) + (6mA × 0.8V)
PD = 18.53mW
Rθ(j-a)of MSOP - 08 package is 206°C / W
Maximum ∆TJ relative to TA due to self heating is 18.53mW × 206°C / W = 3.82°C
Equation 1. Worst-case self-heating
[(0.35mA IDD(typ) × 3.3V) + (25% × 1.5mA IOL(DATA) × 0.3V) + (1% × 1.5mA IOL(/INT) × 0.3V) + (25% × 1.5mA IOL(/CRIT) × 0.3V) = 1.38mW
∆TJ = (1.38mW × 206°C / W) = 0.29°C
Equation 2. Real-world self-heating example
Vendor
Part Number
Package
Fairchild
MMBT3906
SOT-23
On Semiconductor
MMBT3906L
SOT-23
Phillips Semiconductor
PMBT3906
SOT-23
Samsung
KST3906-TF
SOT-23
Table 6. Transistors Suitable for Remote Temperature Sensing Use
MIC284
18
September 29, 2000
MIC284
Micrel
Layout Considerations
The following guidelines should be kept in mind when designing and laying out circuits using the MIC284:
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 to prevent current leakage. This is
most likely to show up as an issue in situations
where water-soluble soldering fluxes are used.
5. In general, wider traces for the ground and T1
lines will help reduce susceptibility to radiated
noise (wider traces are less inductive). Use
trace widths and spacing of 10 mils wherever
possible and provide a ground plane under the
MIC284 and under the connections from the
MIC284 to the remote diode. This will help
guard against stray noise pickup.
6. Always place a good quality power supply
bypass capacitor directly adjacent to, or underneath, the MIC284. This should be a 0.1µF
ceramic capacitor. Surface-mount parts provide
the best bypassing because of their low inductance.
7. When the MIC284 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 7.
1. Place the MIC284 as close to the remote diode
as possible, while taking care to avoid severe
noise sources such as 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 T1 line 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 MIC284’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
MIC284, thereby providing a Kelvin connection
for the base of the diode. See Figure 6.
3. When using the MIC284 to sense the temperature of a processor or other device which has an
integral thermal diode, e.g., Intel’s Pentium III,
connect the emitter and base of the remote
sensor to the MIC284 using the guard traces
and Kelvin return shown in Figure 6. The
collector of the remote diode is typically inaccessible to the user on these devices. To allow for
this, the MIC284 has superb rejection of noise
appearing from collector to GND, as long as the
base to ground connection is relatively quiet.
MIC284
1 DATA
VDD 8
2 CLK
A0 7
3 /INT
T1 6
GUARD/RETURN
REMOTE DIODE (T1)
GUARD/RETURN
4 GND
/CRIT 5
Figure 6. Guard Traces/Kelvin Ground Returns
100
3.3V
0.1µF
10k pull-ups
4.7µF
MIC284
FROM
SERIAL BUS
HOST
OVER-TEMP
SHUTDOWN
DATA
CLK
/INT
VDD
T1
A0
/CRIT
GND
Remote
Diode
2200pF
Figure 7. VDD Decoupling for Very Noisy Supplies
September 29, 2000
19
MIC284
MIC284
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)
0.199 (5.05)
0.187 (4.74)
0.122 (3.10)
0.112 (2.84)
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
0.008 (0.20)
0.004 (0.10)
0.012 (0.03)
0.0256 (0.65) TYP
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)
MICREL INC.
TEL
1849 FORTUNE DRIVE SAN JOSE, CA 95131 USA
+ 1 (408) 944-0800
FAX
+ 1 (408) 944-0970
WEB
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
MIC284
20
September 29, 2000