REV. A
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
a
ADM1023*
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
World Wide Web Site: http://www.analog.com
Fax: 781/326-8703
Analog Devices, Inc., 2000
FUNCTIONAL BLOCK DIAGRAM
ACPI-Compliant
High-Accuracy Microprocessor
System Temperature Monitor
FEATURES
Next Generation Upgrade to ADM1021
On-Chip and Remote Temperature Sensing
Offset Registers for System Calibration
1 C Accuracy and Resolution on Local Channel
0.125 C Resolution/1 C Accuracy on Remote Channel
Programmable Over/Under Temperature Limits
Programmable Conversion Rate
Supports System Management Bus (SMBus) Alert
2-Wire SMBus Serial Interface
200 A Max Operating Current (0.25 Conversions/
Seconds)
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 ADM1023 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.
Optimized for the Pentium
III; the higher accuracy offered
allows systems designers to safely reduce temperature guard
banding and increase system performance. The device can
measure the temperature of a microprocessor using a diode-con-
nected 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 channel measures the
output of an on-chip temperature sensor, to monitor the tem-
perature of the device and its environment.
The ADM1023 communicates over a 2-wire serial interface
compatible with SMBus
standards. Under and over tempera-
ture limits can be programmed into the device 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
interrupt, or as an SMBus alert.
*Patents pending.
Pentium is a registered trademark of Intel Corporation.
ON-CHIP
TEMPERATURE
SENSOR
A-TO-D
CONVERTER
BUSY
RUN/STANDBY
EXTERNAL DIODE OPEN-CIRCUIT
ADDRESS POINTER
REGISTER
ONE-SHOT
REGISTER
CONVERSION RATE
REGISTER
OFFSET
REGISTERS
REMOTE TEMPERATURE
HIGH-LIMIT REGISTERS
CONFIGURATION
REGISTER
INTERRUPT
MASKING
SMBUS INTERFACE
LOCAL TEMPERATURE
LOW-LIMIT COMPARATOR
LOCAL TEMPERATURE
HIGH-LIMIT COMPARATOR
REMOTE TEMPERATURE
LOW-LIMIT COMPARATOR
REMOTE TEMPERATURE
HIGH-LIMIT COMPARATOR
REMOTE TEMPERATURE
VALUE REGISTERS
LOCAL TEMPERATURE
VALUE REGISTER
STATUS REGISTER
NC
V
DD
GND
NC
GND
NC
NC
NC
SDATA
SCLK
ADD0
ADD1
ALERT
STBY
D+
D
REMOTE TEMPERATURE
LOW-LIMIT REGISTERS
LOCAL TEMPERATURE
HIGH-LIMIT REGISTER
LOCAL TEMPERATURE
LOW-LIMIT REGISTER
ANALOG
MUX
NC = NO CONNECT
ADM1023
2
REV. A
ADM1023SPECIFICATIONS
(T
A
= T
MIN
to T
MAX
1
, V
DD
= 3.0 V to 3.6 V, unless otherwise noted)
Parameter
Min
Typ
Max
Unit
Test Conditions/Comments
POWER SUPPLY AND ADC
Temperature Resolution, Local Sensor
1
C
Guaranteed No Missed Codes
Temperature Resolution, Remote Sensor
0.125
C
Guaranteed No Missed Codes
Temperature Error, Local Sensor
1.5
0.5
+1.5
C
T
A
= 60
C to 100C
3
1
+3
C
T
A
= 0
C to 120C
Temperature Error, Remote Sensor
1
+1
C
T
A
, T
D
= 60
C to 100C (Note 2)
3
+3
C
T
A
, T
D
= 0
C to 120C (Note 2)
Relative Accuracy
0.25
C
T
A
= 60
C to 100C
Supply Voltage Range
3
3.6
V
Note 3
Undervoltage Lockout Threshold
2.55
2.7
2.8
V
V
DD
Input, Disables ADC, Rising Edge
Undervoltage Lockout Hysteresis
25
mV
Power-On Reset Threshold
0.9
1.7
2.2
V
V
DD
, Falling Edge (Note 4)
POR Threshold Hysteresis
50
mV
Standby Supply Current
1
5
A
V
DD
= 3.3 V, No SMBus Activity
4
A
SCLK at 10 kHz
Average Operating Supply Current
130
200
A
0.25 Conversions/Sec Rate
Autoconvert Mode, Averaged Over 4 Sec
225
330
A
2 Conversions/Sec Rate
Conversion Time
65
115
170
ms
From Stop Bit to Conversion
Complete (Both Channels)
D+ Forced to D + 0.65 V
Remote Sensor Source Current
120
205
300
A
High Level (Note 4)
7
12
16
A
Low Level (Note 4)
D-Source Voltage
0.7
V
Address Pin Bias Current (ADD0, ADD1)
50
A
Momentary at Power-On Reset
SMBus INTERFACE
Logic Input High Voltage, V
IH
2.2
V
V
DD
= 3 V to 5.5 V
STBY, SCLK, SDATA
Logic Input Low Voltage, V
IL
0.8
V
V
DD
= 3 V to 5.5 V
STBY, SCLK, SDATA
SMBus Output Low Sink Current
6
mA
SDATA Forced to 0.6 V
ALERT Output Low Sink Current
1
mA
ALERT Forced to 0.4 V
Logic Input Current, I
IH
, I
IL
1
+1
A
SMBus Input Capacitance, SCLK, SDATA
5
pF
SMBus Clock Frequency
100
kHz
SMBus Clock Low Time, t
LOW
4.7
s
t
LOW
Between 10% Points
SMBus Clock High Time, t
HIGH
4
ns
t
HIGH
Between 90% Points
SMBus Start Condition Setup Time, t
SU:STA
4.7
ns
SMBus Start Condition Hold Time, t
HD:STA
4
ns
Time from 10% of SDATA to 90%
of SCLK
SMBus Stop Condition Setup Time, t
SU:STO
4
ns
Time from 90% of SCLK to 10%
of SDATA
SMBus Data Valid to SCLK
250
ns
Time for 10% or 90% of
Rising Edge Time, t
SU:DAT
SDATA to 10% of SCLK
SMBus Data Hold Time, t
HD:DAT
0
s
SMBus Bus Free Time, t
BUF
4.7
s
Between Start/Stop Condition
SCLK Falling Edge to SDATA
1
s
Master Clocking in Data
Valid Time, t
VD,DAT
SMBus Leakage Current
5
A
V
DD
= 0 V
NOTES
1
T
MAX
= 120
C, T
MIN
= 0
C
.
2
T
D
is temperature of remote thermal diode; T
A
, T
D
= 60
C to 100C.
3
Operation at V
DD
= 5 V guaranteed by design, not production tested.
4
Guaranteed by design, not production tested.
Specifications subject to change without notice.
ADM1023
3
REV. A
ABSOLUTE MAXIMUM RATINGS
*
Positive Supply Voltage (V
DD
) to GND . . . . . . 0.3 V to +6 V
D+, ADD0, ADD1 . . . . . . . . . . . . . . . 0.3 V to V
DD
+ 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 +125C
Maximum Junction Temperature (T
J
max) . . . . . . . . . . 150
C
Storage Temperature Range . . . . . . . . . . . . 65
C to +150C
Lead Temperature (Soldering 10 sec) . . . . . . . . . . . . . . 300
C
IR Reflow Peak Temperature . . . . . . . . . . . . . . . . . . . . . 220
C
*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 CHARACTERISTICS
16-Lead QSOP Package
JA
= 105
C/W
JC
= 39
C/W
ORDERING GUIDE
Temperature
Package
Package
Model
Range
Description
Option
ADM1023ARQ
0
C to 120C
16-Lead QSOP
RQ-16
PIN FUNCTION DESCRIPTIONS
Pin No.
Mnemonic
Description
1, 5, 9,
NC
No Connect.
13, 16
2
V
DD
Positive supply, 3 V to 5.5 V.
3
D+
Positive connection to remote tem-
perature sensor.
4
D
Negative connection to remote tem-
perature sensor.
6
ADD1
Three-state logic input, higher bit of
device address.
7, 8
GND
Supply 0 V connection.
10
ADD0
Three-state logic input, lower bit of
device address.
11
ALERT
Open-drain logic output used as
interrupt or SMBus alert.
12
SDATA
Logic input/output, SMBus serial
data. Open-drain output.
14
SCLK
Logic input, SMBus serial clock.
15
STBY
Logic input selecting normal opera-
tion (high) or standby mode (low).
PIN CONFIGURATION
TOP VIEW
(Not to Scale)
16
15
14
13
12
11
10
9
1
2
3
4
5
6
7
8
GND
V
DD
NC
ALERT
D+
D
ADM1023
NC
GND
ADD1
NC
NC
ADD0
SDATA
NC
SCLK
STBY
NC = NO CONNECT
P
S
P
t
HD;STA
t
SU;STA
t
SU;DAT
t
HIGH
t
F
t
HD;DAT
t
R
t
LOW
t
HD;STA
t
BUF
S
SCL
SDA
t
SU;STO
Figure 1. Diagram for Serial Bus Timing
ADM1023
4
REV. A
Typical Performance Characteristics
LEAKAGE RESISTANCE M
20
15
25
100
TEMPERATURE ERROR
C
10
1
0
10
15
20
10
5
5
30
D+ TO GND
D+ TO V
DD
Figure 2. Temperature Error vs. Resistance from Track to
V
DD
and GND
3
1
0
2
FREQUENCY Hz
100
TEMPERATURE ERROR
C
4
5
1k
10k
100k
1M
10M
100M
250mV p-p REMOTE
100mV p-p REMOTE
Figure 3. Remote Temperature Error vs. Supply Noise
Frequency
5
4
3
1
0
2
FREQUENCY Hz
1
TEMPERATURE ERROR
C
10
1k
10k
10M
100M
6
7
8
9
100
100k
1M
50mV p-p
100mV p-p
25mV p-p
Figure 4. Temperature Error vs. Common-Mode Noise
Frequency
1
1
3
2
TEMPERATURE C
50
ERROR
C
2
3
60
70
80
90
110
120
0
100
Figure 5. Temperature Error of ADM1023 vs. Pentium III
Temperature
CAPACITANCE nF
1
2
TEMPERATURE ERROR
C
12
14
4
6
8
10
12
14
16
18
20
22
24
0
2
4
6
8
10
Figure 6. Temperature Error vs. Capacitance Between D+
and D
SCLK FREQUENCY kHz
1
SUPPLY CURRENT
A
20
0
V
DD
= 3.3V
5
10
25
50
75
100
1000
250
500
750
40
60
70
50
30
10
V
DD
= 5V
Figure 7. Standby Supply Current vs. SCLK Frequency
ADM1023
5
REV. A
4
0
2
FREQUENCY Hz
TEMPERATURE ERROR
C
10mV p-p
100k
1M
10M
100M
1G
1
3
Figure 8. Temperature Error vs. Differential-Mode Noise
Frequency
CONVERSION RATE Hz
250
0.125
SUPPLY CURRENT
A
0.25
0.5
8
300
350
400
550
4
0.0625
450
500
200
150
100
50
5 VOLTS
3.3 VOLTS
2
1
Figure 9. Operating Supply Current vs. Conversion Rate,
V
DD
= 5 V and 3 V
FUNCTIONAL DESCRIPTION
The ADM1023 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 ADM1023
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 temperature, or the remote temperature sensor. These
signals are digitized by the ADC and the results are stored in
the Local and Remote Temperature Value Registers. Only
the eight most significant bits of the local temperature value
are stored as an 8-bit binary word. The remote temperature value
is stored as an 11-bit, binary word in two registers. The eight
MSBs are stored in the Remote Temperature Value High Byte
Register at address 01h. The three LSBs are stored, left-justified,
in the Remote Temperature Value High Byte Register at
address 10h.
Error sources such as PCB track resistance and clock noise
can introduce offset errors into measurements on the Remote
Channel. To achieve the specified accuracy on this channel,
these offsets must be removed, and two Offset Registers are
provided for this purpose at addresses 11h and 12h.
An offset value may automatically be added to or subtracted
from the measurement by writing an 11 bit, two's complement
value to registers 11h (high byte) and 12h (low byte, left-
justified).
The offset registers default to zero at power-up and will have no
effect if nothing is written to them.
The measurement results are compared with Local and Remote,
High and Low Temperature Limits, stored in six on-chip Limit
Registers. As with the measured value, the local temperature
limits are stored as 8-bit values and the remote temperature limits
as 11-bit values. 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.
Registers can be programmed, and the device controlled and
configured, via the serial System Management Bus. The con-
tents of any register can also be read back via the SMBus.
Control and configuration functions consist of:
Switching the device between normal operation and standby
mode.
Masking or enabling the
ALERT output.
Selecting the conversion rate.
On initial power-up the remote and local temperature values
default to 128
C. Since the device normally powers up convert-
ing, a measure of local and remote temperature is made and these
0
20
SUPPLY VOLTAGE V
0
SUPPLY CURRENT
A
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
40
60
80
100
20
Figure 10. Standby Supply Current vs. Supply Voltage
TIME Seconds
TEMPERATURE
C
0
25
50
75
100
125
REMOTE
TEMPERATURE
INT
TEMPERATURE
0
2
3
4
5
6
7
8
9
10
1
Figure 11. Response to Thermal Shock
ADM1023
6
REV. A
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 output.
This may be cleared in one of two ways:
1. Change both the local and remote lower limits to 128
C
and read the status register (which in turn clears the
ALERT
output).
2. 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 nega-
tive temperature coefficient of a diode, or the base-emitter voltage
of a transistor, operated at constant current. Thus, the temperature
may be obtained from a direct measurement of V
BE
where,
V
nKT
q
I
I
BE
C
S
=
ln
(
)
(1)
Unfortunately, this technique requires calibration to null out
the effect of the absolute value of V
BE
, which varies from device
to device.
The technique used in the ADM1023 is to measure the change
in V
BE
when the device is operated at two different collector
currents.
This is given by:
V
nKT
q
N
BE
=
ln ( )
(2)
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 collector currents
n is the ideality factor of the thermal diode (TD)
To measure
V
BE
, the sensor is switched between operating cur-
rents of I and NI. The resulting waveform is passed through a
low-pass filter to remove noise, then to a chopper-stabilized ampli-
fier that performs the functions of amplification and rectification of
the waveform to produce a dc voltage proportional to
V
BE
. This
voltage is measured by the ADC, which gives a temperature output
in binary format. To further 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.
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 PNP transistor, provided for
temperature 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 from interfering with the
measurement, the more negative terminal of the sensor is not
referenced to ground, but is biased above ground by an inter-
nal 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 2200 pF, but should be no more than 3000 pF. See the
section on Layout Considerations for more information on C1.
SOURCES OF ERRORS ON THERMAL
TRANSISTOR MEASUREMENT METHOD
EFFECT OF IDEALITY FACTOR (n)
The effects of ideality factor (n) and beta (Beta) of the temperature
measured by a thermal transistor are discussed below. For a ther-
mal transistor implemented on a submicron process, such as the
substrate PNP used on a Pentium III processor, the temperature
errors due to the combined effect of the ideality factor and beta are
shown to be less than 3
C. Equation 2 is optimized for a sub-
strate PNP transistor (used as a thermal diode) usually found on
CPUs designed on submicron CMOS processes such as the
Pentium III Processor. There is a thermal diode on board each of
these processors. The n in the Equation 2 represents the ideality
factor of this thermal diode. This ideality factor is a measure of the
deviation of the thermal diode from ideal behavior.
According to Pentium III Processor manufacturing specifica-
tions, measured values of n at 100
C are:
n
MIN
= 1.0057 < n
TYPICAL
= 1.008 < n
MAX
= 1.0125
The ADM1023 takes this ideality factor into consideration
when calculating temperature T
TD
of the thermal diode. The
ADM1023 is optimized for n
TYPICAL
= 1.008; any deviation
on n from this typical value causes a temperature error that is
calculated below for the n
MIN
and n
MAX
of a Pentium III Processor
at T
TD
= 100
C,
T
Kelvin
C
C
MIN
=
+
=
1 0057
1 008
1 008
273 15
100
0 85
.
.
.
(
.
)
.
T
Kelvin
C
C
MAX
=
+
= +
1 0125 1 008
1 008
273 15
100
1 67
.
.
.
(
.
)
.
Thus, the temperature error due variation on n of the thermal
diode for Pentium III Processor is about 2.5
C.
C1*
D+
D
REMOTE
SENSING
TRANSISTOR
I
N I
I
BIAS
V
DD
V
OUT+
TO ADC
V
OUT
BIAS
DIODE
LOW-PASS FILTER
f
C
= 65kHz
CAPACITOR C1 IS OPTIONAL. IT IS ONLY NECESSARY IN NOISY ENVIRONMENTS.
C1 = 2.2nF TYPICAL, 3nF MAX.
*
Figure 12. Input Signal Conditioning
ADM1023
7
REV. A
In general, this additional temperature error of the thermal diode
measurement due to deviations on n from its typical value is
given by,
T
n
Kelvin
T
T
C
TD
TD
=
+
.
.
(
.
),
1 008
1 008
273 15
where
is in
BETA OF THERMAL TRANSISTOR ( )
On Figure 12, the thermal diode is a substrate PNP transistor
where the emitter current is being forced into the device. The
derivation of Equation 2 above assumed that the collector cur-
rents scaled by "N" as the emitter currents were also scaled by
"N." In other words, this assumes that beta (
) of the transistor
is constant for various collector currents. The plot below shows
typical beta variation versus collector current for Pentium III
Processors at 100
C. The maximum beta is 4.5 and varies less
than 1% over the collector current range from 7
A to 300 A.
7
300
I
C
(mA)
MAX
< 4.5
I
C
= I
E
+1
I
E
Figure 13. Variation of
with Collector Currents
Expressing the collector current in terms of the emitter current,
I
C
= I
E
[
/ + 1)] where (300 A) = (7 A)(1 + ), = /
and
= (7 A). Rewriting the equation for V
BE
, to include
the ideality factor "n" and beta "
" we have,
V
nKT
q
N
BE
=
+ +
+
+
ln
(
) (
)
(
)
1
1
1
1
(3)
Beta variations of less than 1% (
< 0.01) contribute to tempera-
ture errors of less than 0.4
C.
TEMPERATURE DATA FORMAT
One LSB of the ADC corresponds to 0.125
C, so the ADM1023
can measure from 0
C to 127.875C. The temperature data for-
mat is shown in Tables I and II.
Table I. Temperature Data Format (Local Temperature
and Remote Temperature High Byte)
Temperature ( C)
Digital Output
0
0 000 0000
1
0 000 0001
10
0 000 1010
25
0 001 1001
50
0 011 0010
75
0 100 1011
100
0 110 0100
125
0 111 1101
127
0 111 1111
Note: The ADM1023 differs from the ADM1021 in that the tem-
perature resolution of the remote channel is improved from 1
C
to 0.125
C, but it cannot measure temperatures below 0C. If
negative temperature measurement is required, the ADM1021
should be used.
The results of the local and remote temperature measurements
are stored in the local and remote temperature value registers,
and are compared with limits programmed into the local and
remote high and low limit registers.
Table II. Extended Temperature Resolution (Remote
Temperature Low Byte)
Extended
Remote Temperature
Resolution ( C)
Low Byte
0.000
0000 0000
0.125
0010 0000
0.250
0100 0000
0.375
0110 0000
0.500
1000 0000
0.625
1010 0000
0.750
1100 0000
0.875
1110 0000
REGISTER FUNCTIONS
The ADM1023 contains registers that are used to store the
results of remote and local temperature measurements, high and
low temperature limits, and to configure and control the device.
A description of these registers follows, and further details are
given in Tables III to VII. It should be noted that most of the
ADM1023's registers are dual port, and have different addresses
for read and write operations. Attempting to write to a read
address, or to read from a write address, will produce an invalid
result. Register addresses above 14h are reserved for future use
or used for factory test purposes and should not be written to.
Address Pointer Register
The Address Pointer Register itself does not have, nor does it
require, an address, as it is the register to which the first data
byte of every Write operation is written automatically. This data
byte is an address pointer that sets up one of the other registers
for the second byte of the Write operation, or for a subsequent
read operation.
Value Registers
The ADM1023 has three registers to store the results of Local
and Remote temperature measurements. These registers are
written to by the ADC and can only be read over the SMBus.
The Offset Register
Two offset registers are provided at addresses 11h and 12h.
These are provided so that the user may remove errors from the
measured values of remote temperature. These errors may be
introduced by clock noise and PCB track resistance.
The offset value is stored as an 11-bit, two's complement value
in Registers 11h (high byte) and 12h (low byte, left-justified).
The value of the offset is negative if the MSB of 11h is 1 and is
positive if the MSB of 11h is 0. This value is added to the remote
temperature. These registers default to zero at power-up and
will have no effect if nothing is written to them. The offset regis-
ter can accept values from 128.875
C to +127.875C. The
ADM1023 detects overflow so the remote temperature value
register won't wrap around +127
C or 128C. Table IV con-
tains a set of example offset values.
ADM1023
8
REV. A
Table IV.
Remote
Remote
Temperature Temperature
Offset Registers
Offset
(Including
(Without
11h
12h
Value
Offset)
Offset)
1111 1100 0000 0000
4
C
14
C
18
C
1111 1111 0000 0000
1
C
17
C
18
C
1111 1111 1110 0000
0.125
C 17.875C
18
C
0000 0000 0000 0000
0
C
18
C
18
C
0000 0000 0010 0000
+0.125
C 18.125C
18
C
0000 0001 0000 0000
+1
C
19
C
18
C
0000 0100 0000 0000
+4
C
22
C
18
C
Status Register
Bit 7 of the Status Register indicates that the ADC is busy con-
verting when it is high. Bits 6 to 3 are flags that indicate the
results of the limit comparisons.
If the local and/or remote temperature measurement is above
the corresponding high temperature limit, or below the corre-
sponding low temperature limit, one or more of these flags will be
set. Bit 2 is a flag that is set if the remote temperature sensor
is open-circuit. These five flags are NOR'd together, so that if
any of them are high, the
ALERT interrupt latch will be set and
the
ALERT output will go low. Reading the Status Register will
clear the five flag bits, provided the error conditions that caused
the flags to be set have gone away. While a limit comparator
is tripped due to a value register containing an out-of-limit
measurement, or the sensor is open-circuit, the corresponding
flag bit cannot be reset. A flag bit can only be reset if the corre-
sponding value register contains an in-limit measurement, or the
sensor is good.
The
ALERT interrupt latch is not reset by reading the Status
Register, but will be reset when the
ALERT output has been
serviced by the master reading the device address, provided the
error condition has gone away and the Status Register flag bits
have been reset.
Table V. Status Register Bit Assignments
Bit
Name
Function
7
BUSY
1 When ADC Converting.
6
LHIGH
*
1 When Local High Temp Limit Tripped.
5
LLOW
*
1 When Local Low Temp Limit Tripped.
4
RHIGH
*
1 When Remote High Temp Limit Tripped.
3
RLOW
*
1 When Remote Low Temp Limit Tripped.
2
OPEN
*
1 When Remote Sensor Open-Circuit.
10
Reserved.
*These flags stay high until the status register is read or they are reset by POR.
Configuration Register
Two bits of the configuration register are used. If Bit 6 is 0, which
is the power-on default, the device is in operating mode with the
ADC converting. If Bit 6 is set to 1, the device is in standby mode
and the ADC does not convert. Standby mode can also be selected
by taking the
STBY pin low. In standby mode the values of remote
and local temperature remain at the value they were before the
part was placed in standby.
Bit 7 of the configuration register is used to mask the
ALERT
output. If Bit 7 is 0, which is the power-on default, the
ALERT
output is enabled. If Bit 7 is set to 1, the
ALERT output is
disabled.
Table III. List of ADM1023 Registers
READ Address (Hex)
WRITE Address (Hex)
Name
Power-On Default
Not Applicable
Not Applicable
Address Pointer
Undefined
00
Not Applicable
Local Temperature Value
1000 0000 (80h) (128
C)
01
Not Applicable
Remote Temperature Value High Byte
1000 0000 (80h) (128
C)
02
Not Applicable
Status
Undefined
03
09
Configuration
0000 0000 (00h)
04
0A
Conversion Rate
0000 0010 (02h)
05
0B
Local Temperature High Limit
0111 1111 (7Fh) (+127
C)
06
0C
Local Temperature Low Limit
1100 1001 (C9h) (55
C)
07
0D
Remote Temperature High Limit High Byte
0111 1111 (7Fh) (+127
C)
08
0E
Remote Temperature Low Limit High Byte
1100 1001 (C9h) (55
C)
Not Applicable
0F
1
One-Shot
10
Not Applicable
Remote Temperature Value Low Byte
0000 0000
11
11
Remote Temperature Offset High Byte
0000 0000
12
12
Remote Temperature Offset Low Byte
0000 0000
13
13
Remote Temperature High Limit Low Byte
0000 0000
14
14
Remote Temperature Low Limit Low Byte
0000 0000
19
Not Applicable
Reserved
0000 0000
20
21
Reserved
Undefined
FE
Not Applicable
Manufacturer Device ID
0100 0001 (41h)
FF
Not Applicable
Die Revision Code
0011 xxxx (3xh)
NOTE
1
Writing to address 0F causes the ADM1023 to perform a single measurement. It is not a data register as such and it does not matter what data is written to it.
ADM1023
9
REV. A
Table VI. Configuration Register Bit Assignments
Power-On
Bit
Name
Function
Default
7
MASK1
0 =
ALERT Enabled
0
1 =
ALERT Masked
6
RUN/STOP
0 = Run
0
1 = Standby
50
Reserved
0
Conversion Rate Register
The lowest three bits of this register are used to program the
conversion rate by dividing the ADC clock by 1, 2, 4, 8, 16, 32,
64, or 128, to give conversion times from 125 ms (Code 07h) to
16 seconds (Code 00h). This register can be written to and read
back over the SMBus. The higher five bits of this register are
unused and must be set to zero. Use of slower conversion times
greatly reduces the device power consumption, as shown in
Table VII.
Table VII. Conversion Rate Register Codes
Average Supply Current
Data
Conversion/sec
A Typ at V
CC
= 3.3 V
00h
0.0625
150
01h
0.125
150
02h
0.25
150
03h
0.5
150
04h
1
150
05h
2
150
06h
4
160
07h
8
180
08h to FFh
Reserved
Limit Registers
The ADM1023 has six limit registers to store local and remote,
high and low temperature limits. These registers can be written
to and read back, over the SMBus. The high limit registers per-
form a > comparison while the low limit registers perform a
< comparison. For example, if the high limit register is programmed
as a limit of 80
C, measuring 81C will result in an alarm condi-
tion. Even though the temperature range is 0 to 127
C, it is
possible to program the Limit Register with negative values.
This is for backwards-compatibility with the ADM1021.
One-Shot Register
The one-shot register is used to initiate a single conversion and
comparison cycle when the ADM1023 is in standby mode, after
which the device returns to standby. This is not a data register as
such and it is the write operation that causes the one-shot conver-
sion. The data written to this address is irrelevant and is not stored.
SERIAL BUS INTERFACE
Control of the ADM1023 is carried out via the serial bus. The
ADM1023 is connected to this bus as a slave device, under the
control of a master device.
ADDRESS PINS
In general, every SMBus device has a 7-bit device address (except
for some devices that have extended, 10-bit addresses). When
the master device sends a device address over the bus, the slave
device with that address will respond. The ADM1023 has two
address pins, ADD0 and ADD1, to allow selection of the device
address, so that several ADM1023s can be used on the same bus,
and/or to avoid conflict with other devices. Although only two
address pins are provided, these are three-state, and can be
grounded, left unconnected, or tied to V
DD
, so that a total of
nine different addresses are possible, as shown in Table VIII.
It should be noted that the state of the address pins is only sampled
at power-up, so changing them after power-up will have no effect.
Table VIII. Device Addresses
ADD0
ADD1
Device Address
0
0
0011 000
0
NC
0011 001
0
1
0011 010
NC
0
0101 001
NC
NC
0101 010
NC
1
0101 011
1
0
1001 100
1
NC
1001 101
1
1
1001 110
ADD0, ADD1 sampled at power-up only.
The serial bus protocol operates as follows:
1. The master initiates data transfer by establishing a START condi-
tion, defined as a high-to-low transition on the serial data line
SDATA, while the serial clock line SCLK 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 determines 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 Acknowledge
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.
2. 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.
3. When all data bytes have been read or written, stop condi-
tions 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 ninth 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.
ADM1023
10
REV. A
In the case of the ADM1023, write operations contain either
one or two bytes, while 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 a valid address that is stored in the Address
Pointer Register. If data is to be written to the device, the write
operation contains a second data byte that is written to the regis-
ter selected by the address pointer register.
This is illustrated in Figure 14. 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:
1. If the ADM1023's Address Pointer Register value is unknown,
or not the desired value, it is first necessary to set it to the
correct value before data can be read from the desired data
register. This is done by performing a write to the ADM1023
as before, but only the data byte containing the register read
address is sent, as data is not to be written to the register.
This is shown in Figure 15.
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 15.
2. 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 15 can be omitted.
NOTES
1. Although 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.
2. Do not forget that ADM1023 registers have different addresses
for read and write operations. The write address of a register
must be written to the Address Pointer if data is to be written
to that register, but it is not possible to read data from that
address. The read address of a register must be written to
the Address Pointer before data can be read from that register.
R/
W
0
SCLK
SDATA
1
0
1
1
A1
A0
D7
D6
D5
D4
D3
D2
D1
D0
ACK. BY
ADM1023
START BY
MASTER
1
9
1
ACK. BY
ADM1023
9
D7
D6
D5
D4
D3
D2
D1
D0
ACK. BY
ADM1023
STOP BY
MASTER
1
9
SCLK (CONTINUED)
SDATA (CONTINUED)
FRAME 3
DATA BYTE
FRAME 1
SERIAL BUS ADDRESS BYTE
FRAME 2
ADDRESS POINTER REGISTER BYTE
Figure 14. Writing a Register Address to the Address Pointer Register, then Writing Data to the Selected Register
R/
W
0
SCLK
SDATA
1
0
1
1
A1
A0
D7
D6
D5
D4
D3
D2
D1
D0
ACK. BY
ADM1023
START BY
MASTER
1
9
1
ACK. BY
ADM1023
9
FRAME 1
SERIAL BUS ADDRESS BYTE
FRAME 2
ADDRESS POINTER REGISTER BYTE
STOP BY
MASTER
Figure 15. Writing to the Address Pointer Register Only
R/
W
SCLK
SDATA
D7
D6
D5
D4
D3
D2
D1
D0
NO ACK.
BY MASTER
START BY
MASTER
9
1
ACK. BY
ADM1023
9
FRAME 1
SERIAL BUS ADDRESS BYTE
STOP BY
MASTER
A6
A5
A4
A3
A2
A1
A0
FRAME 2
DATA BYTE FROM ADM1023
1
Figure 16. Reading Data from a Previously Selected Register
ADM1023
11
REV. A
ALERT OUTPUT
The
ALERT output goes low whenever an out-of limit mea-
surement is detected, or if the remote temperature sensor is
open-circuit. It is an open-drain and requires a 10 k
pull-up to
V
DD
. Several
ALERT outputs can be wire-ANDED together, so
that the common line will go low if one or more of the
ALERT
outputs goes low.
The
ALERT output can be used as an interrupt signal to a pro-
cessor, or it may be used as an
SMBALERT. Slave devices on
the SMBus normally cannot signal to the master they want to
talk, but the
SMBALERT function allows them to do so.
One or more
ALERT outputs are connected to a common
SMBALERT line connected to the master. When the SMBALERT
line is pulled low by one of the devices, the following procedure
occurs as illustrated in Figure 17.
MASTER
RECEIVES
SMBALERT
MASTER SENDS
ARA AND READ
COMMAND
DEVICE SENDS
ITS ADDRESS
NO
ACK
START
ALERT RESPONSE ADDRESS
RD
ACK
DEVICE ADDRESS
STOP
Figure 17. Use of
SMBALERT
1.
SMBALERT pulled low.
2. Master initiates a read operation and sends the Alert Response
Address (ARA = 0001 100). This is a general call address that
must not be used as a specific device address.
3. The device whose
ALERT output is low responds to the Alert
Response Address and the master reads its device address.
The address of the device is now known and it can be inter-
rogated in the usual way.
4. If more than one device's
ALERT output is low, the one with
the lowest device address, will have priority, in accordance
with normal SMBus arbitration.
5. Once the ADM1023 has responded to the Alert Response
Address, it will reset its
ALERT output, provided that the
error condition that caused the
ALERT no longer exists. If the
SMBALERT line remains low, the master will send ARA again,
and so on until all devices whose
ALERT outputs were low
have responded.
LOW POWER STANDBY MODES
The ADM1023 can be put into a low power standby mode using
hardware or software, that is, by taking the
STBY input low, or by
setting Bit 6 of the Configuration Register. When
STBY is high, or
Bit 6 is low, the ADM1023 operates normally. When
STBY is
pulled low or Bit 6 is high, the ADC is inhibited, any conversion in
progress is terminated without writing the result to the correspond-
ing value register.
The SMBus is still enabled. Power consumption in the standby
mode is reduced to less than 10
A if there is no SMBus activ-
ity, or 100
A if there are clock and data signals on the bus.
These two modes are similar but not identical. When
STBY is
low, conversions are completely inhibited. When Bit 6 is set but
STBY is high, a one-shot conversion of both channels can be
initiated by writing any data value to the One-Shot Register
(Address 0Fh).
SENSOR FAULT DETECTION
The ADM1023 has a fault detector at the D+ input that detects
if the external sensor diode is open-circuit. This is a simple voltage
comparator that trips if the voltage at D+ exceeds V
CC
1 V
(typical). The output of this comparator is checked when a conver-
sion is initiated, and sets Bit 2 of the Status Register if a fault is
detected.
If the remote sensor voltage falls below the normal measuring
range, for example, due to the diode being short-circuited, the
ADC will output 128
C (1000 0000 000). Since the normal
operating temperature range of the device only extends down
to 0
C, this output code will never be seen in normal operation,
so it can be interpreted as a fault condition.
In this respect, the ADM1023 differs from and improves upon
competitive devices that output zero if the external sensor goes
short-circuit. These devices can misinterpret a genuine 0
C mea-
surement as a fault condition.
If the external diode channel is not being used and is shorted
out, the resulting
ALERT may be cleared by writing 80h (128
C)
to the low limit register.
APPLICATIONS INFORMATION
FACTORS AFFECTING ACCURACY
Remote Sensing Diode
The ADM1023 is designed to work with substrate transistors
built into processors, or with discrete transistors. Substrate tran-
sistors will generally be PNP types with the collector connected
to the substrate. Discrete types can be either PNP or NPN, con-
nected as a diode (base shorted to collector). If an NPN transistor
is used then the collector and base are connected to D+ and the
emitter to D. If a PNP transistor is used, the collector and base
are connected to D and the emitter to D+.
The user has no choice in the case of substrate transistors, but if
a discrete transistor is used, the best accuracy will be obtained by
choosing devices according to the following criteria:
1. Base-emitter voltage greater than 0.25 V at 6
A, at the high-
est operating temperature.
2. Base-emitter voltage less than 0.95 V at 100
A, at the lowest
operating temperature.
3. Base resistance less than 100 .
4. Small variation in h
fe
(say 50 to 150) which indicates tight
control of V
BE
characteristics.
Transistors such as 2N3904, 2N3906 or equivalents in SOT-23
package are suitable devices to use.
Thermal Inertia and Self-Heating
Accuracy depends on the temperature of the remote-sensing
diode and/or the internal temperature sensor being at the same
temperature as that being measured; and a number of factors
can affect this. Ideally, the sensor should be in good thermal
contact with the part of the system being measured, for example
the processor. If it is not, the thermal inertia caused by the mass
of the sensor will cause a lag in the response of the sensor to a
temperature change. In the case of the remote sensor this should
not be a problem, as it will be either a substrate transistor in the
processor or a small package device such as SOT-23 placed in
close proximity to it.
The on-chip sensor, however, will often be remote from the pro-
cessor and will only be monitoring the general ambient temperature
12
C0005806/00 (rev. A)
PRINTED IN U.S.A.
ADM1023
REV. A
around the package. The thermal time constant of the QSOP-16
package is about 10 seconds.
In practice, the package will have electrical, and hence thermal,
connection to the printed circuit board, so the temperature rise
due to self-heating will be negligible.
LAYOUT CONSIDERATIONS
Digital boards can be electrically noisy environments, and the
ADM1023 is measuring very small voltages from the remote
sensor, so care must be taken to minimize noise induced at the
sensor inputs. The following precautions should be taken:
1. Place the ADM1023 as close as possible to the remote sensing
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.
2. 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.
3. Use wide tracks to minimize inductance and reduce noise
pickup. 10 mil track minimum width and spacing is
recommended.
10MIL
10MIL
10MIL
10MIL
10MIL
10MIL
10MIL
GND
D+
D
GND
Figure 18. Arrangement of Signal Tracks
4. 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 240
V, and thermocouple voltages are
about 3
V/C of temperature difference. Unless there are
two thermocouples with a big temperature differential between
them, thermocouple voltages should be much less than 240
V.
5. Place a 0.1
F bypass capacitor close to the V
DD
pin and
2200 pF input filter capacitors across D+, D close to the
ADM1023.
6. 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.
7. For really long distances (up to 100 feet), use shielded twisted
pair such as Belden #8451 microphone cable. Connect the
twisted pair to D+ and D and the shield to GND close to
the ADM1023. Leave the remote end of the shield uncon-
nected to avoid ground loops.
Because the measurement technique uses switched current sources,
excessive cable and/or filter capacitance can affect the measure-
ment. When using long cables, the filter capacitor may be reduced
or removed.
Cable resistance can also introduce errors. 1
series resistance
introduces about 1
C error.
APPLICATION CIRCUITS
Figure 19 shows a typical application circuit for the ADM1023,
using a discrete sensor transistor connected via a shielded, twisted
pair cable. The pull-ups on SCLK, SDATA, and
ALERT are required
only if they are not already provided elsewhere in the system.
The SCLK and SDATA pins of the ADM1023 can be interfaced
directly to the SMBus of an I/O chip. Figure 20 shows how the
ADM1023 might be integrated into a system using this type of
I/O controller.
ALERT
GND
ADD0
D+
D
ADM1023
OUT
SCLK
SDATA
ADD1
V
DD
I/O
SET TO
REQUIRED
ADDRESS
IN
3V
TO 5.5V
2200pF
10k
10k
TO
CONTROL
CHIP
10k
0.1 F
SHIELD
2N3904
Figure 19. Typical ADM1023 Application Circuit
USB
2 USB PORTS
ICH I/O
CONTROLLER
HUB
CD ROM
HARD
DISK
SYSTEM
MEMORY
PROCESSOR
GMCH
DISPLAY
DISPLAY
CACHE
ADM1023
SCLK
SDATA
ALERT
D+
D
SYSTEM BUS
PCI BUS
PCI SLOTS
USB
FWH
(FIRMWARE
HUB)
SUPER I/O
SMBUS
2 IDE PORTS
Figure 20. Typical System Using ADM1023
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
16-Lead QSOP
(RQ-16)
16
9
8
1
0.197 (5.00)
0.189 (4.80)
0.244 (6.20)
0.228 (5.79)
PIN 1
0.157 (3.99)
0.150 (3.81)
SEATING
PLANE
0.010 (0.25)
0.004 (0.10)
0.012 (0.30)
0.008 (0.20)
0.025
(0.64)
BSC
0.059 (1.50)
MAX
0.069 (1.75)
0.053 (1.35)
0.010 (0.20)
0.007 (0.18)
0.050 (1.27)
0.016 (0.41)
8
0
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