ADM1021AARQ Fast Delivery |IC PHOENIX CO.,LIMITED

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ADM1021AARQ
Low-Cost Microprocessor System Temperature Monitor
REV.A
FUNCTIONAL BLOCK DIAGRAM
Low-Cost Microprocessor
System Temperature Monitor*
FEATURES
Alternative to the ADM1021
On-Chip and Remote Temperature Sensing
No Calibration Necessary
1�C Accuracy for On-Chip Sensor
3�C Accuracy for Remote Sensor
Programmable Over/Under Temperature Limits
Programmable Conversion Rate
2-Wire SMBus Serial Interface
Supports System Management Bus (SMBus) Alert
200 �A Max Operating Current
1 �A Standby Current
3 V to 5.5 V Supply
Small 16-Lead QSOP Package
APPLICATIONS
Desktop Computers
Notebook Computers
Smart Batteries
Industrial Controllers
Telecomms Equipment
Instrumentation
PRODUCT DESCRIPTION
The ADM1021A is a two-channel digital thermometer and under/
over temperature alarm, intended for use in personal computers
and other systems requiring thermal monitoring and management.
The device can measure the temperature of a microprocessor
using a diode-connected PNP transistor, which may be provided
on-chip in the case of the Pentium® III or similar processors,
or can be a low-cost discrete NPN/PNP device such as the
2N3904/2N3906. A novel measurement technique cancels out
the absolute value of the transistor’s base emitter voltage, so
that no calibration is required. The second measurement chan-
nel measures the output of an on-chip temperature sensor, to
monitor the temperature of the device and its environment.
The ADM1021A communicates over a two-wire serial interface
compatible with SMBus standards. Under and over temperature
limits can be programmed into the devices over the serial bus,
and an ALERT output signals when the on-chip or remote
temperature is out of range. This output can be used as an inter-
rupt, or as an SMBus alert.
*Patents Pending.
Pentium is a registered trademark of Intel Corporation.
ADM1021A–SPECIFICATIONS(TA = TMIN to TMAX1, VDD = 3.0 V to 3.6 V, unless otherwise noted.)
NOTESTMAX = 100°C; TMIN = 0°C.Operation at VDD = 5 V guaranteed by design, not production tested.Guaranteed by design, not production tested.
Specifications subject to change without notice.
ABSOLUTE MAXIMUM RATINGS*
Positive Supply Voltage (VDD) to GND . . . . . . –0.3 V to +6 V
D+, ADD0, ADD1 . . . . . . . . . . . . . . . –0.3 V to VDD + 0.3 V
D– to GND . . . . . . . . . . . . . . . . . . . . . . . . . . –0.3 V to +0.6 V
SCLK, SDATA, ALERT, STBY . . . . . . . . . . . –0.3 V to +6 V
Input Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .±50 mA
Input Current, D– . . . . . . . . . . . . . . . . . . . . . . . . . . . . ±1 mA
ESD Rating, All Pins (Human Body Model) . . . . . . . . 2000 V
Continuous Power Dissipation
Up to 70°C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 650 mW
Derating above 70°C . . . . . . . . . . . . . . . . . . . . . 6.7 mW/°C
Operating Temperature Range . . . . . . . . . . –55°C to +125°C
Maximum Junction Temperature (TJ max) . . . . . . . . . . 150°C
Storage Temperature Range . . . . . . . . . . . . –65°C to +150°C
Lead Temperature, (Soldering 10 sec) . . . . . . . . . . . . .300°C
IR Reflow Peak Temperature . . . . . . . . . . . . . . . . . . . . . 220°C
PIN FUNCTION DESCRIPTIONS
PIN CONFIGURATION
Figure 1.Diagram for Serial Bus Timing
LEAKAGE RESISTANCE – M�
TEMPERATURE ERROR
�C1
–30
Figure 2.Temperature Error vs. PC Board Track Resistance
FREQUENCY – Hz
TEMPERATURE ERROR
�C
100M1k10k100k1M10M
Figure 3.Temperature Error vs. Power Supply Noise
Frequency
FREQUENCY – Hz
TEMPERATURE ERROR
�C1k10k10M100M
100100k1M
Figure 4.Temperature Error vs. Common-Mode Noise
Frequency
Figure 5.Temperature Error of ADM1021A vs.
Pentium III Temperature
CAPACITANCE – nF
TEMPERATURE ERROR
�C681012141618202224
Figure 6.Temperature Error vs. Capacitance Between
D+ and D–
SCLK FREQUENCY – kHz
SUPPLY CURRENT 102550751001000250500750
Figure 7.Standby Supply Current vs. Clock Frequency
ADM1021A–Typical Performance Characteristics
FREQUENCY – Hz
TEMPERATURE ERROR
�C
100k1M10M100M1G
Figure 8.Temperature Error vs. Differential-Mode Noise
Frequency
Figure 9.Operating Supply Current vs. Conversion Rate
SUPPLY VOLTAGE – V
SUPPLY CURRENT
–20
Figure 10.Standby Supply Current vs. Supply Voltage
Figure 11.Response to Thermal Shock
FUNCTIONAL DESCRIPTION
The ADM1021A contains a two-channel A-to-D converter with
special input-signal conditioning to enable operation with remote
and on-chip diode temperature sensors. When the ADM1021A
is operating normally, the A-to-D converter operates in a free-
running mode. The analog input multiplexer alternately selects
either the on-chip temperature sensor to measure its local tem-
perature, or the remote temperature sensor. These signals are
digitized by the ADC and the results stored in the Local and
Remote Temperature Value Registers as 8-bit, two's comple-
ment words.
The measurement results are compared with Local and Remote,
High and Low Temperature Limits, stored in four on-chip regis-
ters. Out-of-limit comparisons generate flags that are stored in
the status register, and one or more out-of-limit results will
cause the ALERT output to pull low.
The limit registers can be programmed, and the device con-
trolled and configured, via the serial System Management Bus.
The contents of any register can also be read back via the SMBus.
Control and configuration functions consist of:Selecting the conversion rate.
On initial power-up, the Remote and Local Temperature values
default to –128°C. Since the device normally powers up converting,
a measurement of local and remote temperature is made and these
values are then stored before a comparison with the stored limits
is made. However, if the part is powered up in standby mode
(STBY pin pulled low), no new values are written to the register
before a comparison is made. As a result, both RLOW and LLOW
are tripped in the Status Register thus generating an ALERT out-
put. This may be cleared in one of two ways:Change both the local and remote lower limits to –128°C
and read the status register (which in turn clears the
ALERT output).Take the part out of standby and read the status register
(which in turn clears the ALERT output). This will work
only if the measured values are within the limit values.
MEASUREMENT METHOD
A simple method of measuring temperature is to exploit the
negative temperature coefficient of a diode, or the base-emitter
ADM1021A
Figure 12.Input Signal Conditioning
The technique used in the ADM1021A 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 electron (1.6 × 10–19 Coulombs),
T is absolute temperature in Kelvins,
N is ratio of the two currents.
Figure 12 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 tem-
perature 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 and should be linked to
the base. To prevent ground noise interfering with the measure-
ment, 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 operating in a noisy environment,
C1 may optionally be added as a noise filter. Its value is typically
2200pF, but should be no more than 3000pF. See the section
on layout considerations for more information on C1.
To measure ∆VBE, the sensor is switched between operating
currents of I and N × I. The resulting waveform is passed through akHz low-pass filter to remove noise, then to a chopper-
stabilized amplifier that performs the functions of amplification
and rectification of the waveform to produce a dc voltage propor-
tional to ∆VBE. This voltage is measured by the ADC to give a
temperature output in 8-bit two's complement format. To fur-
ther reduce the effects of noise, digital filtering is performed by
averaging the results of 16 measurement cycles.
Signal conditioning and measurement of the internal temperature
sensor is performed in a similar manner.
DIFFERENCES BETWEEN THE ADM1021 AND THE
ADM1021A
Although the ADM1021A is pin-for-pin compatible with theThe ADM1021A forces a larger current through the remote
temperature sensing diode, typically 205 µA versus 90 µA
for the ADM1021. The main reason for this is to improve
the noise immunity of the part.As a result of the greater Remote Sensor Source Current the
operating current of the ADM1021A is higher than that of
the ADM1021, typically 205 mA versus 160 mA.The temperature measurement range of the ADM1021A is
0°C to 127°C, compared with –128°C to +127°C for the
ADM1021. As a result, the ADM1021 should be used if
negative temperature measurement is required.The power-on-reset values of the remote and local tempera-
ture values are –128°C in the ADM1021A as compared with
0°C in the ADM1021. As the part is powered up converting
(except when the part is in standby mode, i.e., Pin 15 is
pulled low) the part will measure the actual values of remote
and local temperature and write these to the registers.The four MSBs of the Revision Register may be used to
identify the part. The ADM1021 Revision Register reads
0xh and the ADM1021A reads 3xh.The power-on default value of the Address Pointer Register
is undefined in the ADM1021A and is equal to 00h in the
ADM1021. As a result, a value must be written to the Address
Pointer Register before a read is done in the ADM1021A.
The ADM1021 is capable of reading back local temperature
without writing to the Address Pointer Register as it defaulted
to the local temperature measurement register at power-up.Setting the mask bit (Bit 7 Config Reg) on the ADM1021A
will mask current and future ALERTs. On the ADM1021
the mask bit will only mask future ALERTs. Any current
ALERT will have to be cleared using an ARA.
TEMPERATURE DATA FORMAT
One LSB of the ADC corresponds to 1°C, so the ADC can
theoretically measure from –128°C to +127°C, although the
device does not measure temperatures below 0°C so the actual
range is 0°C to 127°C. The temperature data format is shown in
Table I.
The results of the local and remote temperature measurements

Partno	Mfg	Dc	Qty	Available	Descript
ADM1021AARQ		N/a	97	avai	Low-Cost Microprocessor System Temperature Monitor