Low-Cost Microprocessor
a
FEATURES
Alternative to the ADM1021
On-Chip and Remote Temperature Sensing
No Calibration Necessary
1ⴗC Accuracy for On-Chip Sensor
3ⴗC Accuracy for Remote Sensor
Programmable Overtemperature/Undertemperature
Limits
Programmable Conversion Rate
2-Wire SMBus Serial Interface
Supports System Management Bus (SMBus) Alert
200 mA Max Operating Current
1 mA Standby Current
3 V to 5.5 V Supply
Small 16-Lead QSOP Package
APPLICATIONS
Desktop Computers
Notebook Computers
Smart Batteries
Industrial Controllers
Telecom Equipment
Instrumentation
System Temperature Monitor
*
ADM1021A
PRODUCT DESCRIPTION
The ADM1021A is a two-channel digital thermometer and
undertemperature/overtemperature 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
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 temperature of the device and its environment.
The ADM1021A communicates over a two-wire serial interface
compatible with SMBus
standards. Undertemperature and
overtemperature 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 interrupt, or as an SMBus alert.
®
III or similar
D+
D–
*Patents Pending
ON-CHIP TEMP.
SENSOR
ANALOG MUX
EXTERNAL DIODE OPEN-CIRCUIT
ADM1021A
NC
NC GND NC NC
V
DD
LOCAL TEMPERATURE
VALUE REGISTER
A-TO-D
CONVERTER
BUSY RUN/STANDBY
REMOTE TEMPERATURE
VALUE REGISTER
GND
FUNCTIONAL BLOCK DIAGRAM
LOCAL TEMPERATURE
LOW LIMIT COMPARATOR
LOCAL TEMPERATURE
HIGH LIMIT COMPARATOR
REMOTE TEMPERATURE
LOW LIMIT COMPARATOR
REMOTE TEMPERATURE
HIGH LIMIT COMPARATOR
STATUS REGISTER
SMBUS INTERFACE
NC
SDATA
SCLK ADD0 ADD1
ADDRESS POINTER
REGISTER
ONE-SHOT
REGISTER
CONVERSION RATE
REGISTER
LOCAL TEMPERATURE
LOW LIMIT REGISTER
LOCAL TEMPERATURE
HIGH LIMIT REGISTER
REMOTE TEMPERATURE
LOW LIMIT REGISTER
REMOTE TEMPERATURE
HIGH LIMIT REGISTER
CONFIGURATION
REGISTER
INTERRUPT
MASKING
NC = NO CONNECT
STBY
ALERT
REV. D
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 that
may result from its use. No license is granted by implication or otherwise
under any patent or patent rights of Analog Devices. Trademarks and
registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700 www.analog.com
Fax: 781/326-8703 © 2004 Analog Devices, Inc. All rights reserved.
ADM1021A–SPECIFICATIONS
(TA = T
MIN
1
to T
, VDD = 3.0 V to 3.6 V, unless otherwise noted.)
MAX
Parameter Min Typ Max Unit Test Conditions/Comments
POWER SUPPLY AND ADC
Temperature Resolution 1 °C Guaranteed No Missed Codes
Temperature Error, Local Sensor ± 1 °C
–3 +3 °C
Temperature Error, Remote Sensor –3 +3 °CT
= 60°C to 100°C
A
–5 +5 °C
Supply Voltage Range 3 3.6 V Note 2
Undervoltage Lockout Threshold 2.5 2.7 2.95 V V
Undervoltage Lockout Hysteresis 25 mV
Power-On Reset Threshold 0.9 1.7 2.2 V V
Input, Disables ADC, Rising Edge
DD
, Falling Edge
DD
3
POR Threshold Hysteresis 50 mV
Standby Supply Current 1 5 µAV
= 3.3 V, No SMBus Activity
DD
4 µA SCLK at 10 kHz
Average Operating Supply Current 130 200 µA 0.25 Conversions/Sec Rate
Autoconvert Mode, Averaged Over 4 Seconds 225 330 µA2 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 µAHigh Level
71216µALow Level
3
3
D-Source Voltage 0.7 V
Address Pin Bias Current (ADD0, ADD1) 50 µAMomentary at Power-On Reset
SMBUS INTERFACE
Logic Input High Voltage, V
IH
2.2 V VDD = 3 V to 5.5 V
STBY, SCLK, SDATA
Logic Input Low Voltage, V
IL
0.8 V VDD = 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
, I
IH
IL
–1 +1 µA
SMBus Input Capacitance, SCLK, SDATA 5 pF
SMBus Clock Frequency 100 kHz
SMBus Clock Low Time, t
SMBus Clock High Time, t
SMBus Start Condition Setup Time, t
LOW
HIGH
SU:STA
4.7 µst
4 µst
4.7 µs
between 10% Points
LOW
between 90% Points
HIGH
SMBus Repeat Start Condition 250 ns Between 90% and 90% Points
Setup Time, t
SMBus Start Condition Hold Time, t
SMBus Stop Condition Setup Time, t
SU:STA
HD:STA
SU:STO
4 µsTime from 10% of SDATA to 90% of SCLK
4 µsTime from 90% of SCLK to 10% of SDATA
SMBus Data Valid to SCLK 250 ns Time from 10% or 90% of SDATA to 10%
Rising Edge Time, t
SU:DAT
SMBus Data Hold Time, t
SMBus Bus Free Time, t
BUF
HD:DAT
0 µs
4.7 µsBetween Start/Stop Conditions
of SCLK
SCLK Falling Edge to SDATA 1 µsMaster Clocking in Data
Valid Time, t
NOTES
1
T
= 100°C; T
MAX
2
Operation at VDD = 5 V guaranteed by design, not production tested.
3
Guaranteed by design, not production tested.
Specifications subject to change without notice.
MIN
VD, DAT
= 0°C.
–2–
REV. D
ADM1021A
TOP VIEW
(Not to Scale)
NC = NO CONNECT
NC
V
DD
D+
D–
NC
ADD1
GND
GND
NC
STBY
SCLK
NC
SDATA
ALERT
ADD0
NC
ADM1021A
16
15
14
13
12
11
10
9
1
2
3
4
5
6
7
8
ABSOLUTE MAXIMUM RATINGS*
Positive Supply Voltage (VDD) to GND . . . . . . –0.3 V to +6 V
D+, ADD0, ADD1 . . . . . . . . . . . . . . . –0.3 V to V
+ 0.3 V
DD
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 (T
max) . . . . . . . . . . 150°C
J
Storage Temperature Range . . . . . . . . . . . . –65°C to +150°C
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: θ
= 150°C/W.
JA
ORDERING GUIDE
PIN FUNCTION DESCRIPTIONS
Pin No. Mnemonic Description
1, 5, 9, 13, 16 NC No Connect
2V
DD
Positive Supply, 3 V to 5.5 V
3D+Positive Connection to Remote
Temperature Sensor
4D–Negative Connection to Remote
Temperature Sensor
6ADD1 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
Operation (High) or Standby Mode
(Low)
PIN CONFIGURATION
Model Temperature Package Package
Range Description Option
ADM1021AARQ 0°C to 100°C 16-Lead QSOP RQ-16
ADM1021AARQ-REEL 0°C to 100°C 16-Lead QSOP RQ-16
ADM1021AARQ-REEL7 0°C to 100°C 16-Lead QSOP RQ-16
ADM1021AARQZ* 0°C to 100°C 16-Lead QSOP RQ-16
ADM1021AARQZ-REEL* 0°C to 100°C 16-Lead QSOP RQ-16
ADM1021AARQZ-REEL7* 0°C to 100°C 16-Lead QSOP RQ-16
EVAL-ADM1021AEB Evaluation Board
* Z = Pb-Lead free
t
R
t
HD;DAT
t
HIGH
t
F
SCL
SDA
t
LOW
t
HD;STA
t
BUF
S
P
Figure 1. Diagram for Serial Bus Timing
t
SU;DAT
t
SU;STA
t
HD;STA
t
SU;STO
PS
CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily
accumulate on the human body and test equipment and can discharge without detection. Although the
ADM1021A 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.
REV. D
–3–
ADM1021A–Typical Performance Characteristics
20
15
10
5
0
–5
–10
–15
TEMPERATURE ERROR – ⴗC
–20
–25
–30
D+ TO GND
D+ TO V
DD
LEAKAGE RESISTANCE – M⍀
101
100
2
1
–1
TEMPERATURE ERROR – ⴗC
–2
–3
60070
50
80
TEMPERATURE – ⴗC
UPPER SPEC LEVEL
DEV10
LOWER SPEC LEVEL
100
90
110
120
TPC 1. Temperature Error vs. PC Board Track Resistance
5
4
250mV p-p REMOTE
3
2
TEMPERATURE ERROR – ⴗC
1
0
100
100mV p-p REMOTE
FREQUENCY – Hz
100M1k 10k 100k 1M 10M
TPC 2. Temperature Error vs. Power Supply Noise
Frequency
9
8
7
6
5
4
3
TEMPERATURE ERROR – ⴗC
2
1
0
10 1k 10k
1
100 100k 1M
100mV p-p
50mV p-p
FREQUENCY – Hz
25mV p-p
10M 100M
TPC 4. Temperature Error of ADM1021A vs. Pentium
III Temperature
14
12
10
8
6
4
2
TEMPERATURE ERROR – ⴗC
0
–1
2
4681012141618202224
CAPACITANCE – nF
TPC 5. Temperature Error vs. Capacitance Between D+
and D–
70
60
50
40
30
20
SUPPLY CURRENT – A
10
0
1
510255075100 1000250 500 750
SCLK FREQUENCY – kHz
VDD = 3.3V
VDD = 5V
TPC 3. Temperature Error vs. Common-Mode Noise
Frequency
–4–
TPC 6. Standby Supply Current vs. Clock Frequency
REV. D
ADM1021A
TIME – Seconds
TEMPERATURE – ⴗC
0
25
50
75
100
125
REMOTE
TEMPERATURE
INT
TEMPERATURE
023456789101
4
3
10mV p-p
2
1
TEMPERATURE ERROR – ⴗC
0
100k 1M
10M 100M 1G
FREQUENCY – Hz
TPC 7. Temperature Error vs. Differential-Mode Noise
Frequency
550
500
450
400
350
300
250
200
SUPPLY CURRENT – A
150
100
50
0.125
0.25 0.5 8
CONVERSION RATE – Hz
3.3V
5V
40.0625
21
100
80
60
40
20
SUPPLY CURRENT – A
0
–20
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
SUPPLY VOLTAGE – V
TPC 9. Standby Supply Current vs. Supply Voltage
TPC 8. Operating Supply Current vs. Conversion Rate
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 temperature, 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, twos complement words.
The measurement results are compared with local and remote,
high and low temperature limits, stored in four on-chip registers.
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 controlled 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:
•
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 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:
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
negative temperature coefficient of a diode, or the base-emitter
voltage of a transistor, operated at constant current. Unfortunately, this technique requires calibration to null out the effect
of the absolute value of V
TPC 10. Response to Thermal Shock
, which varies from device to device.
BE
REV. D
–5–
ADM1021A
IN ⴛ I I
BIAS
V
DD
D+
REMOTE
SENSING
TRANSISTOR
C1*
D–
*
CAPACITOR C1 IS OPTIONAL. IT IS ONLY NECESSARY IN NOISY ENVIRONMENTS.
C1 = 2.2nF TYPICAL, 3nF MAX.
BIAS
DIODE
Figure 2. Input Signal Conditioning
The technique used in the ADM1021A is to measure the change
when the device is operated at two different currents.
in V
BE
This is given by:
∆V
= KT/q × ln(N)
BE
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 2 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. 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 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 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.
To measure ∆V
, the sensor is switched between operating currents
BE
of I and N × I. The resulting waveform is passed through a 65 kHz
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 proportional to ∆V
. This
BE
voltage is measured by the ADC to give a temperature output in
8-bit twos complement format. To reduce the effects of noise
further, 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 the
ADM1021, there are some differences between the two devices.
Below is a summary of these differences and reasons for the changes.
1. The ADM1021A forces a larger current through the remote
temperature sensing diode, typically 205 µA versus 90 µA
V
OUT+
TO ADC
V
LOWPASS FILTER
f
= 65kHz
C
OUT–
for the ADM1021. The main reason for this is to improve
the noise immunity of the part.
2. 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.
3. 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.
4. The power-on reset values of the remote and local temperature 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.
5. 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.
6. 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.
7. 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
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.
–6–
REV. D
ADM1021A
Table I. Temperature Data Format
Temperature Digital Output
0°C0 000 0000
1°C0 000 0001
10°C0 000 1010
25°C0 001 1001
50°C0 011 0010
75°C0 100 1011
100°C0 110 0100
125°C0 111 1101
127°C0 111 1111
REGISTERS
The ADM1021A contains nine 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 II to IV. It should be noted that the
ADM1021A’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 0Fh 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 ADM1021A has two 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.
Status Register
Bit 7 of the Status Register indicates when it is high that the
ADC is busy converting. Bits 5 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 corresponding
low temperature limit, then one or more of these flags will be set.
Bit 2 is a flag that is set if the remote temperature sensor is opencircuit. These five flags are NOR’d together, so that if any of them
is 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 corresponding value register contains an in-limit measurement, or the sensor is good.
Table II. 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
1–0 Reserved
*These flags stay high until the status register is read or they are reset by POR.
Table III. List of ADM1021A Registers
READ Address (Hex) WRITE Address (Hex) Name Power-On Default
Not Applicable Not Applicable Address Pointer Undefined
00 Not Applicable Local Temp. Value 1000 0000 (80h) (–128°C)
01 Not Applicable Remote Temp. Value 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 Temp. High Limit 0111 1111 (7Fh) (+127°C)
06 0C Local Temp. Low Limit 1100 1001 (C9h) (–55°C)
07 0D Remote Temp. High Limit 0111 1111 (7Fh) (+127°C)
08 0E Remote Temp. Low Limit 1100 1001 (C9h) (–55°C)
Not Applicable 0F
10 Not Applicable Reserved Undefined
11 11 Reserved Undefined
12 12 Reserved Undefined
13 13 Reserved Undefined
14 14 Reserved Undefined
15 16 Reserved Undefined
17 18 Reserved Undefined
19 Not Applicable Reserved Undefined
20 21 Reserved Undefined
1
One-Shot
2
2
2
2
2
2
2
2
2
FE Not Applicable Manufacturer Device ID 0100 0001 (41h)
FF Not Applicable Die Revision Code 0011 xxxx (3xh)
NOTES
1
Writing to address 0F causes the ADM1021A to perform a single measurement. It is not a data register as such and it does not matter what data is written to it.
2
These registers are reserved for future versions of the device.
REV. D
–7–
ADM1021A
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.
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 stored in the Remote and Local Temperature Registers remain
at the value they were when the part was placed in standby.
Bit 7 of the configuration register is used to mask the ALERT out-
put. 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 IV. 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
5–0 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 V.
Table V. Conversion Rate Register Codes
Average Supply Current
Data Conversion/secµA Typ at VCC = 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 ADM1021A has four 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
perform 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 81°C will result in an
alarm condition. Even though the temperature measurement
range is from 0ⴗ 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 ADM1021A 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 oneshot conversion. The data written to this address is irrelevant and
is not stored.
SERIAL BUS INTERFACE
Control of the ADM1021A is carried out via the serial bus. The
ADM1021A is connected to this bus as a slave device, under the
control of a master device. Note that the SMBus and SCL pins
are three-stated when the ADM1021A is powered down and will
not pull down the SMBus.
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 ADM1021A has two
address pins, ADD0 and ADD1, to allow selection of the device
address, so that several ADM1021As 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
, so that a total of
DD
nine different addresses are possible, as shown in Table VI.
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 VI. Device Addresses
ADD0 ADD1 Device Address
00 0011 000
0NC 0011 001
01 0011 010
NC 0 0101 001
NC NC 0101 010
NC 1 0101 011
10 1001 100
1NC 1001 101
11 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
condition, 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.
–8–
REV. D
ADM1021A
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 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
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.
191
SCLK
A6
SDATA
START BY
MASTER
A5 A4 A3 A2 A1 A0 D7
FRAME 1
SERIAL BUS ADDRESS BYTE
SCL (CONTINUED)
R/W
ACK. BY
ADM1021A
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 ADM1021A, write operations contain either
one or two bytes, while read operations contain one byte.
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, data can then 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 register selected by the address pointer register.
9
D6
D5 D4 D3 D2 D1
ADDRESS POINTER REGISTER BYTE
1
FRAME 2
D0
ACK. BY
ADM1021A
9
SDA (CONTINUED)
D7 D6
D5 D4 D3 D2 D1
FRAME 3
DATA BYTE
D0
ACK. BY
ADM1021A
STOP BY
MASTER
Figure 3. Writing a Register Address to the Address Pointer Register, then Writing Data to the Selected Register
191
SCLK
SDATA A5 A4
START BY
MASTER
A6
SERIAL BUS ADDRESS BYTE
A3 A2
FRAME 1
A1 A0
R/W
ACK. BY
ADM1021A
D7 D6
D4
D5
ADDRESS POINTER REGISTER BYTE
FRAME 2
D3
D2
D1
9
D0
ACK. BY
ADM1021A
STOP BY
MASTER
Figure 4. Writing to the Address Pointer Register Only
SCLK
SDATA
START BY
MASTER
19
A6
A5 A4 A3 A2 A1 A0 D7
FRAME 1
SERIAL BUS ADDRESS BYTE
R/W
ADM1021A
ACK. BY
1
D6
D5
D4 D3
FRAME 2 DATA BYTE FROM ADM1021A
D2
D1 D0
9
NO ACK.
BY MASTER
STOP BY
MASTER
REV. D
Figure 5. Reading Data from a Previously Selected Register
–9–
ADM1021A
This is illustrated in Figure 3. 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 ADM1021A’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 ADM1021A
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 4.
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 5.
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 Register,
so Figure 4 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. Remember that the ADM1021A 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.
ALERT OUTPUT
The ALERT output goes low whenever an out-of-limit measurement is detected, or if the remote temperature sensor is
open-circuit. It is an open-drain and requires a 10 kΩ pull-up to
. Several ALERT outputs can be wire-ANDed together, so
V
DD
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 processor, or it may be used as an SMBALERT. Slave devices on
the SMBus can normally not signal to the master that 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 6.
MASTER
RECEIVES
SMBALERT
NO
START ALERT RESPONSE ADDRESSRDACK DEVICE ADDRESS
MASTER SENDS
ARA AND READ
COMMAND
Figure 6. Use of
DEVICE SENDS
ITS ADDRESS
SMBALERT
ACK
STOP
–10–
1. SMBALERT is 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 interrogated
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 ADM1021A 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 the
ARA again, and so on until all devices whose ALERT outputs
were low have responded.
LOW POWER STANDBY MODES
The ADM1021A 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 ADM1021A operates normally.
When STBY is pulled low or Bit 6 is high, the ADC is inhibited,
so any conversion in progress is terminated without writing the
result to the corresponding value register.
The SMBus is still enabled. Power consumption in the standby
mode is reduced to less than 10 µA if there is no SMBus activity,
or 100 µA 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 XXh to the One-Shot Register (address 0Fh).
SENSOR FAULT DETECTION
The ADM1021A 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
– 1V (typical). The output of this comparator is checked
V
CC
when a conversion 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). 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 ADM1021A 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
measurement 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.
REV. D
ADM1021A
APPLICATIONS INFORMATION
FACTORS AFFECTING ACCURACY
Remote Sensing Diode
The ADM1021A is designed to work with substrate transistors
built into processors, or with discrete transistors. Substrate
transistors will generally be PNP types with the collector connected
to the substrate. Discrete types can be either PNP or NPN,
connected as a diode (base shorted to collector). If an NPN
transistor is used, 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 µA, at the high-
est operating temperature.
2. Base-emitter voltage less than 0.95 V at 100 µA, at the lowest
operating temperature.
3. Base resistance less than 100 Ω.
4. Small variation in h
control of V
BE
(say 50 to 150), which indicates tight
FE
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
processor and will only be monitoring the general ambient temperature 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 because
the ADM1021A is measuring very small voltages from the
remote sensor, care must be taken to minimize noise induced at
the sensor inputs. The following precautions should be taken:
1. Place the ADM1021A 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.
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– paths
and at the same temperature.
Thermocouple effects should not be a major problem as 1°C
corresponds to about 240 µV, and thermocouple voltages are
about 3 µV/°C of temperature difference. Unless there are
two thermocouples with a big temperature differential between
them, thermocouple voltages should be much less than 240 µV.
5. Place a 0.1 µF bypass capacitor close to the V
pin, and
DD
2200 pF input filter capacitors across D+, D– close to the
ADM1021A.
GND
D+
D–
GND
10 mil
10 mil
10 mil
10 mil
10 mil
10 mil
10 mil
Figure 7. Arrangement of Signal Tracks
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.
REV. D
–11–
ADM1021A
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 ADM1021A. 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 may be
reduced or removed.
Cable resistance can also introduce errors. 1 Ω series resistance
introduces about 1°C error.
APPLICATION CIRCUITS
Figure 8 shows a typical application circuit for the ADM1021A,
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.
PROCESSOR
SYSTEM BUS
DISPLAY
DISPLAY
CACHE
CD ROM
2 IDE PORTS
USB USB
2 USB PORTS
HARD
DISK
GMCH
ICH
I/O CONTROLLER
HUB
FWH
(FIRMWARE HUB)
PCI BUS
The SCLK and SDATA pins of the ADM1021A can be interfaced directly to the SMBus of an I/O chip. Figure 9 shows how
the ADM1021A might be integrated into a system using this
type of I/O controller.
C1*
2N3904
*C1 IS OPTIONAL
SHIELD
ADM1021A
D+
D–
GND
V
STBY
SCLK
SDATA
ALERT
ADD0
ADD1
DD
0.1F
SET TO REQUIRED
ADDRESS
3.3V
ALL 10k⍀
IN
I/O
OUT
TO CONTROL
CHIP
Figure 8. Typical Application Circuit
D– D+
ADM1021A
SDATA
SCLK
SMBUS
SYSTEM
MEMORY
PCI SLOTS
SUPER
I/O
ALERT
Figure 9. Typical System Using ADM1021A
–12–
REV. D
OUTLINE DIMENSIONS
16-Lead Shrink Small Outline Package [QSOP]
(RQ-16)
Dimensions shown in inches
0.193
BSC
ADM1021A
0.065
0.049
0.010
0.004
COPLANARITY
0.004
0.012
0.008
9
8
0.154
BSC
0.069
0.053
SEATING
PLANE
0.236
BSC
0.010
0.006
16
1
PIN 1
0.025
BSC
COMPLIANT TO JEDEC STANDARDS MO-137AB
8ⴗ
0ⴗ
0.050
0.016
REV. D
–13–
ADM1021A
Revision History
Location Page
3/04—Data Sheet changed from REV. C to REV. D.
Changes to FEATURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Updated Ordering Guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Change to Figure 9 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4/03—Data Sheet changed from REV. B to REV. C.
Added ESD Caution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Updated OUTLINE DIMENSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3/02—Data Sheet changed from REV. A to REV. B.
Figures and TPCs renumbered . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . UNIVERSAL
Text Change to Figure 9 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Change to SERIAL BUS INTERFACE section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
–14–
REV. D
ADM1021A
REV. D
–15–
ADM1021A
C00056–0–3/04(D)
–16–
Loading...