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ADM1022ARQ-REEL-ADM1022ARQ-REEL7
Remote Dual Channel Temperature Sensor, Fan Control and Power Good Detection with Serial Interface
REV.B
Low-Cost PC Temperature
Monitor and Fan Control ASIC
FUNCTIONAL BLOCK DIAGRAMRST1
RST2
D1+
D1–
D2+/GPI
D2–/THERM
GND
SDA
SCL
ADD/NTEST_OUT
VCCVMON
FAN_SPD/NTEST_IN
INT
FAN_OFF
FEATURES
External Temperature Measurement with Remote
Diode (Two Channels)
On-Chip Temperature Sensor
Interrupt and Over-Temperature Outputs
Fault Tolerant Fan Control
Brownout Detection
LDCM Support
System Management Bus (SMBus)
Standby Mode to Minimize Power Consumption
Limit Comparison of all Monitored Values
APPLICATIONS
Network Servers and Personal Computers
Microprocessor-Based Office Equipment
Test Equipment and Measuring Instruments
GENERAL DESCRIPTIONThe ADM1022 is a low cost temperature monitor and fan con-
troller for microprocessor-based systems. The temperature of one
or two remote sensor diodes may be measured, allowing monitor-
ing of processor temperature in single- or dual-processor systems.
Measured values can be read out via a serial System Manage-
ment Bus, and values for limit comparisons can be programmed
in over the same serial bus.
The ADM1022 also contains a DAC for fan speed control.
Automatic hardware temperature trip points are provided and
the fan will be driven to full speed if they are exceeded.
Finally, the chip has two supply voltage monitors for brownout
detection.
The ADM1022’s 3.0 V to 5.5 V supply voltage range, low supply
current, and SMBus interface make it ideal for a wide range of
applications. These include hardware monitoring and protection
applications in personal computers, electronic test equipment
and office electronics.
ADM1022–SPECIFICATIONSTEMPERATURE-TO-DIGITAL CONVERTER
RESET OUTPUTS, RST1, RST2
DIGITAL OUTPUT ADD/NTEST_OUT
(TA = TMIN to TMAX, VCC = VMIN to VMAX, unless otherwise noted.)
ADM1022NOTESTypicals are at TA = 25∞C and represent most likely parametric norm. Standby current typ is measured with VCC = 3.3 V.ADD is a three-state input that may be pulled high, low or left open-circuit.Timing specifications are tested at logic levels of VIL = 0.8 V for a falling edge and VIH = 2.2 V for a rising edge.
Specifications subject to change without notice.
Figure 1.Diagram for Serial Bus Timing
ADM1022
ABSOLUTE MAXIMUM RATINGS*Positive Supply Voltage (VCC) . . . . . . . . . . . . . . . . . . . . 6.5 V
Voltage On Digital Inputs Except Therm . . –0.3 V to +6.5 V
Voltage On Therm Pin . . . . . . . . . . . . –0.3 V to VCC + 0.3 V
Voltage on Any Other Input
or Output Pin . . . . . . . . . . . . . . . . . . –0.3 V to VCC + 0.3 V
Input Current at Any Pin . . . . . . . . . . . . . . . . . . . . . . .±5 mA
Package Input Current . . . . . . . . . . . . . . . . . . . . . . .±20 mA
Maximum Junction Temperature (TJ max) . . . . . . . . . .150∞C
Storage Temperature Range . . . . . . . . . . . . –65∞C to +150∞C
Lead Temperature, Soldering
Vapor Phase 60 sec . . . . . . . . . . . . . . . . . . . . . . . . . . 215∞C
Infrared 15 sec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200∞C
ESD Rating (Human Body Model) . . . . . . . . . . . . . . . 4000 V
*Stresses above those listed under Absolute Maximum Ratings may cause perma-
nent damage to the device. This is a stress rating only; functional operation of the
device at these or any other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute maximum rating
conditions for extended periods may affect device reliability.
THERMAL CHARACTERISTICS16-Lead QSOP PackageqJA = 105∞C/WqJA = 39∞C/W
ORDERING GUIDE
PIN CONFIGURATION
CAUTIONESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000V readily
accumulate on the human body and test equipment and can discharge without detection.
Although the ADM1022 features proprietary ESD protection circuitry, permanent damage may
occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD
precautions are recommended to avoid performance degradation or loss of functionality.
PIN FUNCTION DESCRIPTIONS
ADM1022TPC 1.Temperature Error vs. PC Leakage Resistance
FREQUENCY – Hz50M500
TEMPERATURE ERROR – 50k500k5MTPC 2.Temperature Error vs. Power Supply Noise
Frequency
TPC 3.Temperature Error vs. Common-Mode Noise
Frequency
–Typical Performance CharacteristicsTPC 4.Pentium® III Temperature Measurement vs.
ADM1022 Reading
TPC 5.Temperature Error vs. Capacitance Between D+
and D–
TPC 6.Standby Current vs. Clock Frequency
TPC 7.Temperature Error vs. Differential-Mode Noise
Frequency
TPC 8.Standby Supply Current vs. Supply Voltage
TPC 9.Power-up Reset vs. Temperature
GENERAL DESCRIPTIONThe ADM1022 is a low-cost temperature monitor and fan con-
troller for microprocessor-based systems. The temperature of
one or two remote sensor diodes may be measured, allowing
monitoring of processor temperature in single- or dual-processor
systems. The chip also contains an on-chip sensor to allow
ambient temperature to be monitored.
Measured values can be read out via a serial System Manage-
ment Bus, and values for limit comparisons can be programmed
in over the same serial bus.
The ADM1022 also contains a DAC for fan speed control.
Automatic hardware temperature trip points are provided for
fault tolerant fan control and the fan will be driven to full speed
if they are exceeded. Two interrupt outputs are provided, which
will be asserted if the software or hardware limits are exceeded.
Finally, the chip has two supply voltage monitors for brownout
detection. These drive two reset pins, one of which is bidirec-
tional. A manual reset input is also provided.
INTERNAL REGISTERS OF THE ADM1022A brief description of the ADM1022’s principal internal regis-
ters is given below. More detailed information on the function
of each register is given in Tables IV to IX.
Configuration Register:Provides control and configuration.
Address Pointer Register:This register contains the address that
selects one of the other internal registers. When writing to the
ADM1022, the first byte of data is always a register address, which
is written to the Address Pointer Register.
Interrupt (INT) Status Register:This register provides status
of each Interrupt event. It is also mirrored by a second register
at address 4Ch.
Interrupt (INT) Mask Register:Allows masking of individual
interrupt sources.
Value and Limit Registers: The results of temperature measure-ments are stored in these registers, along with their limit values.
Analog Output Register: The code controlling the analog out-put DAC is stored in this register.
SERIAL BUS INTERFACEControl of the ADM1022 is carried out via the serial bus. The
ADM1022 is connected to this bus as a slave device, under the
control of a master device, e.g., the PIIX4.
The ADM1022 has a 7-bit serial bus address. When the device is
powered up, it will do so with a default serial bus address. The five
MSBs of the address are set to 01011, the two LSBs are deter-
mined by the logical states of Pin 13 (ADD/NTEST_OUT).
This is a three-state input that can be grounded, connected to VCC
or left open-circuit to give three different addresses. The state of
the ADD pin is only sampled at power-up, so changing ADD
with power-on will have no effect until the device is powered
off then on again.
ADM1022
Table I.ADD Pin Truth TableIf ADD is left open-circuit the default address will be 0101100.
The facility to make hardwired changes to A1 and A0 allows the
user to avoid conflicts with other devices sharing the same serial
bus; for example, if more than one ADM1022 is used in a system.
The serial bus protocol operates as follows:The master initiates data transfer by establishing a START
condition, defined as a high-to-low transition on the serial
data line SDA while the serial clock line SCL remains high.
This indicates that an address/data stream will follow. All
slave peripherals connected to the serial bus respond to the
START condition, and shift in the next eight bits, consisting
of a 7-bit address (MSB first) plus an R/W bit, which deter-
mines the direction of the data transfer, i.e., whether data
will be written to or read from the slave device.
The peripheral whose address corresponds to the transmitted
address responds by pulling the data line low during the low
period before the ninth clock pulse, known as the Acknowl-
edge Bit. All other devices on the bus now remain idle while
the selected device waits for data to be read from or written
to it. If the R/W bit is a 0, the master will write to the slave
device. If the R/W bit is a one, the master will read from the
slave device.Data is sent over the serial bus in sequences of nine clock
pulses, eight bits of data followed by an Acknowledge Bit
from the slave device. Transitions on the data line must
occur during the low period of the clock signal and remain
stable during the high period, as a low-to-high transition when
the clock is high may be interpreted as a STOP signal. The
number of data bytes that can be transmitted over the serial
bus in a single READ or WRITE operation is limited only by
what the master and slave devices can handle.When all data bytes have been read or written, stop conditions
are established. In WRITE mode, the master will pull the
data line high during the 10th clock pulse to assert a STOP
condition. In READ mode, the master device will override
the acknowledge bit by pulling the data line high during the
low period before the 9th clock pulse. This is known as No
Acknowledge. The master will then take the data line low
during the low period before the 10th clock pulse, then high
during the 10th clock pulse to assert a STOP condition.
Any number of bytes of data may be transferred over the serial
bus in one operation, but it is not possible to mix read and write
in one operation, because the type of operation is determined at
the beginning and cannot subsequently be changed without
starting a new operation.
In the case of the ADM1022, write operations contain either
one or two bytes, and read operations contain one byte, and
perform the following functions:
To write data to one of the device data registers or read data
from it, the Address Pointer Register must be set so that the
correct data register is addressed, then data can be written into
that register or read from it. The first byte of a write operation
always contains an address that is stored in the Address Pointer
Register. If data is to be written to the device, then the write
operation contains a second data byte that is written to the reg-
ister selected by the address pointer register.
This is illustrated in Figure 2a. The device address is sent over
the bus followed by R/W set to 0. This is followed by two data
bytes. The first data byte is the address of the internal data
register to be written to, which is stored in the Address Pointer
Register. The second data byte is the data to be written to the
internal data register.
When reading data from a register there are two possibilities:If the ADM1022’s Address Pointer Register value is unknown
or not the desired value, it is first necessary to set it to the cor-
rect value before data can be read from the desired data register.
This is done by performing a write to the ADM1022 as before,
but only the data byte containing the register address is sent,
as data is not to be written to the register. This is shown in
Figure 2b.
A read operation is then performed consisting of the serial bus
address, R/W bit set to 1, followed by the data byte read from
the data register. This is shown in Figure 2c.If the Address Pointer Register is known to be already at the
desired address, data can be read from the corresponding
data register without first writing to the Address Pointer Reg-
ister, so Figure 2b can be omitted.
NOTESAlthough it is possible to read a data byte from a data register
without first writing to the Address Pointer Register, if the
Address Pointer Register is already at the correct value, it is
not possible to write data to a register without writing to the
Address Pointer Register, because the first data byte of a
write is always written to the Address Pointer Register.In Figures 2a to 2c, the serial bus address is shown as the
default value 01011(A1)(A0), where A1 and A0 are set by
the three-state ADD pin.
3. The ADM1022 also supports the Read Byte protocol, as
described in the System Management Bus specification.
Figure 2a.Writing a Register Address to the Address Pointer Register, then Writing Data to the Selected Register
SCL
SDA
ACK. BY
ADM1022START BY
MASTER1
ACK. BY
ADM1022
BYTE
STOP BY
MASTERFigure 2b.Writing to the Address Pointer Register Only
SCL
SDA
NO ACK.
BY MASTERSTART BY
MASTER1
ACK. BY
ADM1022
BYTE
STOP BY
MASTERFigure 2c.Reading Data from a Previously Selected Register
TEMPERATURE MEASUREMENT SYSTEM
Internal Temperature MeasurementThe ADM1022 contains an on-chip bandgap temperature
sensor. The on-chip ADC performs conversions on the out-
put of this sensor and outputs the temperature data in 8-bit
twos complement format. The format of the temperature data
is shown in Table II.
External Temperature MeasurementThe ADM1022 can measure the temperature of two external
diode sensors or diode-connected transistors, connected to Pins
9 and 10 or 11 and 12.
Pins 9 and 10 are a dedicated temperature input channel. The
default function of Pins 11 and 12 is the THERM input/output
and a general purpose logic input (GPI), but they can be config-
The forward voltage of a diode or diode-connected transistor,
operated at a constant current, exhibits a negative temperature
coefficient of about –2 mV/∞C. Unfortunately, the absolute value
of VBE, varies from device to device, and individual calibra-
tion is required to null this out, so the technique is unsuitable
for mass-production.
The technique used in the ADM1022 is to measure the change
in VBE when the device is operated at two different currents.
This is given by:
DVBE = KT/q ¥ ln(N)
where:
K is Boltzmann’s constant
ADM1022Figure 3 shows the input signal conditioning used to measure
the output of an external temperature sensor. This figure
shows the external sensor as a substrate transistor, provided
for temperature monitoring on some microprocessors, but it
could equally well be a discrete transistor.
Figure 3.Signal Conditioning
If a discrete transistor is used, the collector will not be grounded,
and should be linked to the base. If a PNP transistor is used the
base is connected to the D– input and the emitter to the D+ input.
If an NPN transistor is used, the emitter is connected to the D–
input and the base to the D+ input.
Table II. Temperature Data Format–125∞C
–100∞C
–75∞C
–50∞C
–25∞C
–1∞C
0∞C
+1∞C
+10∞C
+25∞C
+50∞C
+75∞C
+100∞C
+125∞C
To prevent ground noise interfering with the measurement, the
more negative terminal of the sensor is not referenced to ground,
but is biased above ground by an internal diode at the D– input.
If the sensor is used in a very noisy environment, a capacitor of
value up to 1000 pF may be placed between the D+ and D–
inputs to filter the noise.
To measure DVBE, the sensor is switched between operating
currents of I and N ¥ I. The resulting waveform is passed through
a 65 kHz low-pass filter to remove noise, thence to a chopper-
stabilized amplifier that performs the functions of amplification
and rectification of the waveform to produce a dc voltage pro-
portional to DVBE. This voltage is measured by the ADC to give
LAYOUT CONSIDERATIONSDigital boards can be electrically noisy environments, and care
must be taken to protect the analog inputs from noise, particu-
larly when measuring the very small voltages from a remote
diode sensor. The following precautions should be taken:Place the ADM1022 as close as possible to the remote sens-
ing diode. Provided that the worst noise sources such as
clock generators, data/address buses and CRTs are avoided,
this distance can be four to eight inches.Route the D+ and D– tracks close together, in parallel, with
grounded guard tracks on each side. Provide a ground plane
under the tracks if possible.Use wide tracks to minimize inductance and reduce noise
pickup. 10 mil track minimum width and spacing is
recommended.
Figure 4.Arrangement of Signal TracksTry to minimize the number of copper/solder joints, which
can cause thermocouple effects. Where copper/solder joints
are used, make sure that they are in both the D+ and D–
path and at the same temperature.
Thermocouple effects should not be a major problem as 1∞C
corresponds to about 200 mV, and thermocouple voltages are
about 3 mV/oC of temperature difference. Unless there are
two thermocouples with a big temperature differential between
them, thermocouple voltages should be much less than 200mV.Place 0.1 mF bypass and 1000 pF input filter capacitors close
to the ADM1022.If the distance to the remote sensor is more than eight inches,
the use of twisted pair cable is recommended. This will work
up to about 6 to 12 feet.For really long distances (up to 100 feet) use a shielded
twisted pair such as Belden #8451 microphone cable. Con-
nect the twisted pair to D+ and D– and the shield to GND
close to the ADM1022. Leave the remote end of the shield
unconnected to avoid ground loops.
Because the measurement technique uses switched current
sources, excessive cable and/or filter capacitance can affect the
measurement. When using long cables, the filter capacitor C1
may be reduced or removed. In any case, the total shunt capaci-
tance should not exceed 1000 pF.
Cable resistance can also introduce errors. 1 W series resistance
introduces about 0.5∞C error.
