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ADM1028ARQ
Remote Thermal Diode Monitor with Linear Fan Control
REV. A
Remote Thermal Diode
Monitor with Linear Fan Control
FUNCTIONAL BLOCK DIAGRAM
R_OFF
R_RST
SDA
SCL
RST
VCC3AUX
FAN_SPD/NTEST_IN
INT
FAN_OFF
THERMA/NTEST_OUT
AUXRST
THERMB
GPIGND
FEATURES
On-Chip Temperature Sensor
External Temperature Measurement with Remote Diode
Interrupt and Over-Temperature Outputs
Fault-Tolerant Fan Control with Auto Hardware Trip Point
Remote Reset and Power-Down Functions
LDCM Support
System Management Bus (SMBus) Communications
Standby Mode to Minimize Power Consumption
Limit Comparison of all Monitored Values
DAC Output for Linear Fan Speed Control
Ramp Rate Register for Control of Rate of Change of
Fan Speed, Reduction of Fan Acoustics
APPLICATIONS
Network Servers and Personal Computers
Microprocessor-Based Office Equipment
Test Equipment and Measuring Instruments
GENERAL DESCRIPTIONThe ADM1028 is a low-cost temperature monitor and fan
controller for microprocessor-based systems. The temperature
of a remote sensor diode may be measured, allowing monitoring
of processor temperature in single processor systems. An on-chip
temperature sensor monitors ambient system temperature.
Measured values can be read out via the System Management
Bus, and values for limit comparisons can be programmed in
over the same serial bus.
The ADM1028 also contains a DAC for fan speed control. An
automatic hardware temperature trip point is provided and the fan
will be driven to full speed if it is exceeded. A Ramp Rate Register
is provided to control the rate with which fan speed is increased or
decreased. This is to eliminate sudden changes in fan speed,
thereby reducing fan acoustics and prolonging the fan’s life.
Finally, the chip has remote reset and power-down functionality,
allowing it to be remotely shut down via the SMBus.
The ADM1028’s 3.0 V to 5.5 V supply voltage range, low
supply current, and SMBus make it ideal for a wide range of
applications. These include hardware monitoring applications
in PCs, electronic test equipment, and office electronics.
ADM1028–SPECIFICATIONS1, 2
(TA = TMIN to TMAX, VCC = VMIN to VMAX, unless otherwise noted.)TEMPERATURE-TO-DIGITAL CONVERTER
DIGITAL INPUT LOGIC LEVELS
ADM1028NOTESTypicals are at TA = 25°C and represent most likely parametric norm. Standby current typ is measured with VCC = 3.3 V.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.IOH for FAN_OFF guaranteed by design, not production tested.Guaranteed by design, not production tested.
Specifications subject to change without notice.
ABSOLUTE MAXIMUM RATINGS*Positive Supply Voltage (VCC) . . . . . . . . . . . . . . . . . . . . . 6.5 V
Voltage on Digital Inputs Except Therm
and D– . . . . . . . . . . . . . . . . . . . . . . . . . . . . –0.3 V to +6.5 V
Voltage on Therm Pin . . . . . . . . . . . . . . –0.3 V to VCC + 0.3 V
Voltage on D– Pin . . . . . . . . . . . . . . . . . . . . –0.3 V to + 0.6 V
Voltage on Any Other Input . . . . . . . . . . –0.3 V to VCC + 0.3 V
or Output Pin
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 Temperatures
Soldering (10 sec) . . . . . . . . . . . . . . . . . . . . . . . . . . . 300°C
IR Reflow Peak Temperature . . . . . . . . . . . . . . . . . . . 220°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 Package:
θJA = 105°C/W, θJC = 39°C/W
ORDERING GUIDEFigure 1.Serial Bus Timing Diagram
ADM1028
PIN FUNCTION DESCRIPTIONS
PIN CONFIGURATION
LEAKAGE RESISTANCE – M�
TEMPERATURE ERROR
�C
–10TPC 1.Temperature Error vs. PC Board Track Resistance
(D+ to VDD)
TPC 2.Temperature Error vs. Power Supply
Noise Frequency
TPC 3.Temperature Error vs. Common-Mode
Noise Frequency
TEMPERATURE – �C
ERROR
�C102030405060708090–5
100TPC 4.Temperature Error of ADM1028 vs. Pentium® III
Temperature
CAPACITANCE – nF
TEMPERATURE ERROR
�C10203040506070–5TPC 5.Temperature Error vs. Capacitance Between
D+ and D–
TPC 6.Standby Current vs. Clock Frequency
ADM1028
FREQUENCY – Hz
TEMPERATURE ERROR
�C1k1M1010010k100k10M100M1BTPC 7.Temperature Error vs. Differential-Mode
Noise Frequency
TEMPERATURE – �C
STANDBY SUPPLY CURRENT
mA
–20020406080100130–10–301030507090120TPC 8.Standby Supply Current vs. Temperature
FUNCTIONAL DESCRIPTIONThe ADM1028 is a low-cost temperature monitor and fan con-
troller for microprocessor-based systems. The temperature of
a remote sensor diode may be measured, allowing monitoring
of processor temperature in a single-processor system. An on-
chip temperature sensor allows monitoring of system ambient
temperature.
Measured values can be read out via the serial System Manage-
ment Bus, and values for limit comparisons can be programmed
in over the same serial bus.
The ADM1028 also contains a DAC for fan speed control. An
automatic hardware temperature trip point is provided for fault
tolerant fan control and the fan will be driven to full speed if this
is exceeded. Two interrupt outputs are provided, which will be
asserted if the software or hardware limits are exceeded.
Finally, the chip has remote reset and shutdown capabilities.
INTERNAL REGISTERS OF THE ADM1028A brief description of the ADM1028’s principal internal registers
is given below. More detailed information on the function of
each register is given in Tables III 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 ADM1028, 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 sta-
tus of each Interrupt event.
Interrupt (INT) Mask Register:Allows masking of individual
interrupt sources.
Value and Limit Registers:The results of temperature mea-
surements are stored in these registers, along with their limit values.
Analog Output Register: The code controlling the analogoutput DAC is stored in this register.
Alert Status Register: Indicates the status of the THERM
Fan Speed Ramp Register: This register allows enabling/disabling of DAC ramp, as well as providing control of fan
speed ramp rate.
SERIAL BUS INTERFACEControl of the ADM1028 is carried out via the serial bus. The
ADM1028 is connected to this bus as a slave device, under the
control of a master device, e.g. the 810 chipset.
The ADM1028 has a 7-bit serial bus address. When the device
powers up, it will do so with a default serial bus address. The
SMBus address for the ADM1028 is 0101110 binary.
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 1, 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 num-
ber of data bytes that can be transmitted over the serial bus
in a single READ or WRITE operation is limited only by
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 ninth clock pulse. This is
known as No Acknowledge. The master will then take the
data line low during the low period before the tenth clock
pulse, then high during the tenth 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 ADM1028, 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, the write opera-
tion contains a second data byte that is written to the register
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 is only one possibility:The serial bus address is written to the device along with the
address pointer register value. The ADM1028 should then
acknowledge the write by pulling SDA low during the ninth
clock pulse. The master does not generate a STOP condition
but issues a new START condition. The serial bus address
is again sent but with the R/W bit high, indicating a READ
operation. The ADM1028 will then return the data from the
selected register, and a No Acknowledge is generated to signify
the end of the read operation. The master will then initiate a
STOP condition to end the transaction and release the SMBus.
In Figures 2a and 2b, the serial bus address is shown as the
default value 0101110.
Figure 2a.Writing a Register Address to the Address Pointer Register, then Writing Data to the Selected Register
ADM1028
TEMPERATURE MEASUREMENT SYSTEM
Internal Temperature MeasurementThe ADM1028 contains an on-chip bandgap temperature sen-
sor. The on-chip ADC performs conversions on the output of
this sensor and outputs the temperature data in 8-bit two’s
complement format. The format of the temperature data is
shown in Table I.
Table I.Temperature Data Format
External Temperature MeasurementThe ADM1028 can measure the temperature of an external
diode sensor or diode-connected transistor, connected to Pins 9
and 10.
Pins 9 and 10 are a dedicated temperature input channel. The
default functions of Pins 11 and 12 are as THERM outputs to
indicate over-temperature conditions.
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 calibration
is required to null this out, making the technique unsuitable
for mass production.
The technique used in the ADM1028 is to measure the change
in VBE when the device is operated at two different currents.
This is given by:
∆VBE = KT/q × ln(N)
where:
K is Boltzmann’s constant.
q is charge on the carrier.
T is absolute temperature in Kelvins.
N is ratio of the two currents.
Figure 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 tempera-
ture monitoring on some microprocessors, but it could equally
well be a discrete transistor.
If a discrete transistor is used, the collector will not be grounded,
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 ∆VBE, 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 proportional to ∆VBE. This voltage is measured by the
ADC to give a temperature output in 8-bit two’s complement
format. To further reduce the effects of noise, digital filtering is
performed by averaging the results of 16 measurement cycles.
An external temperature measurement nominally takes 9.6 ms.
Figure 3.Signal Conditioning
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 ADM1028 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 4 to 8 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. Ten mil track minimum width and spacing is rec-
ommended.Try 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 µV, and thermocouple voltages are
about 3 µV/oC of temperature difference. Unless there are
two thermocouples with a big temperature differential between
them, thermocouple voltages should be much less than 200 µV.Place 0.1 µF bypass and 2200 pF input filter capacitors close
to the ADM1028.
