ADM1021A D

ADM1021A
Low Cost Microprocessor
System Temperature
Monitor Microcomputer
The ADM1021A is a two-channel digital thermometer and
under/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 can be provided on-chip with
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 temperature of the device and its environment.
The ADM1021A communicates over a two-wire serial interface
compatible with SMBus standards. Under/overtemperature 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.
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QSOP 16
CASE 492
PIN ASSIGNMENT
NC
1
16
NC
VDD
2
15
STBY
D+
3
14
SCLK
Features
D−
4
13
NC














NC
5
12
SDATA
ADD1
6
11
ALERT
GND
7
10
ADD0
GND
8
9
NC
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/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
3.0 V to 5.5 V Supply
Small 16-lead QSOP Package
This Device is Pb-Free, Halogen Free and is RoHS Compliant
Applications






July, 2012 − Rev. 9
NC = No Connect
MARKING DIAGRAM
1021AA
RQZ
YYWWG
1021AARQZ
YY
WW
G
Desktop Computers
Notebook Computers
Smart Batteries
Industrial Controllers
Telecom Equipment
Instrumentation
 Semiconductor Components Industries, LLC, 2012
ADM1021A
(Top View)
= Specific Device Code
= Year
= Work Week
= Pb-Free Package
ORDERING INFORMATION
See detailed ordering and shipping information in the package
dimensions section on page 15 of this data sheet.
1
Publication Order Number:
ADM1021A/D
ADM1021A
ADDRESS POINTER
REGISTER
ONE-SHOT
REGISTER
CONVERTION RATE
REGISTER
ON-CHIP
TEMPERATURE
SENSOR
D+
3
D−
4
LOCAL TEMPERATURE
VALUE REGISTER
A-TO-D
CONVERTER
ANALOG
MUX
BUSY
RUN/STANDBY
REMOTE TEMPERATURE
VALUE REGISTER
LOCAL TEMPERATURE
LOW LIMIT COMPARATOR
LOCAL TEMPERATURE
LOW LIMIT REGISTER
LOCAL TEMPERATURE
HIGH LIMIT COMPARATOR
LOCAL TEMPERATURE
HIGH LIMIT REGISTER
REMOTE TEMPERATURE
LOW LIMIT COMPARATOR
REMOTE TEMPERATURE
LOW LIMIT REGISTER
REMOTE TEMPERATURE
HIGH LIMIT COMPARATOR
REMOTE TEMPERATURE
HIGH LIMIT REGISTER
CONFIGURATION
REGISTER
EXTERNAL DIODE OPEN-CIRCUIT
INTERRUPT
MASKING
STATUS REGISTER
15 STBY
11 ALERT
ADM1021A
SMBus INTERFACE
1
2
5
7
8
9
13
16
12
14
10
6
NC
VDD
NC
GND
GND
NC
NC
NC
SDATA
SCLK
ADD0
ADD1
NC = NO CONNECT
Figure 1. Functional Block Diagram
Table 1. PIN ASSIGNMENT
Pin No.
Mnemonic
Description
1
NC
No Connect
2
VDD
Positive Supply, 3.0 V to 5.5 V
3
D+
Positive Connection to Remote Temperature Sensor
4
D−
Negative Connection to Remote Temperature Sensor
5
NC
No Connect
6
ADD1
Three-state Logic Input, Higher Bit of Device Address
7
GND
Supply 0 V Connection
8
GND
Supply 0 V Connection
9
NC
10
ADD0
No Connect
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
13
NC
14
SCLK
Logic Input, SMBus Serial Clock
15
STBY
Logic Input Selecting Normal Operation (High) or Standby Mode (Low)
16
NC
No Connect
No Connect
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ADM1021A
Table 2. ABSOLUTE MAXIMUM RATINGS
Parameter
Positive Supply Voltage (VDD) to GND
D+, ADD0, ADD1
Rating
Unit
−0.3 to +6.0
V
−0.3 to VDD + 0.3
V
D− to GND
−0.3 to +0.6
SCLK, SDATA, ALERT, STBY
−0.3 to +6.0
V
50
mA
Input Current
Input Current, D−
1
mA
2,000
V
Continuous Power Dissipation
Up to 70C
Derating Above 70C
650
6.7
mW
mW/C
Operating Temperature Range
−55 to +125
C
150
C
ESD Rating, All Pins (Human Body Model)
Maximum Junction Temperature (TJ MAX)
Storage Temperature Range
−65 to +150
C
Lead Temperature, Soldering (10 sec)
300
C
IR Reflow Peak Temperature
220
C
Stresses exceeding Maximum Ratings may damage the device. Maximum Ratings are stress ratings only. Functional operation above the
Recommended Operating Conditions is not implied. Extended exposure to stresses above the Recommended Operating Conditions may affect
device reliability.
NOTE: This device is ESD sensitive. Use standard ESD precautions when handling.
Table 3. THERMAL CHARACTERISTICS
Package Type
16-lead QSOP Package
qJA
Unit
105
C/W
Table 4. ELECTRICAL CHARACTERISTICS
(TA = TMIN to TMAX, VDD = 3.0 V to 3.6 V, unless otherwise noted) (Note 1)
Parameter
Test Conditions/Comments
Min
Typ
Max
Unit
1.0
−
−
C
−3.0
1.0
+3.0
C
−3.0
−5.0
−
−
+3.0
+5.0
C
3.0
−
3.6
V
2.5
2.7
2.95
V
−
25
−
mV
0.9
1.7
2.2
V
−
50
−
mV
Power Supply and ADC
Temperature Resolution
Guaranteed No Missed Codes
Temperature Error, Local Sensor
Temperature Error, Remote Sensor
TA = 60C to 100C
Supply Voltage Range (Note 2)
Undervoltage Lockout Threshold
VDD Input, Disables ADC, Rising Edge
Undervoltage Lockout Hysteresis
Power-On Reset Threshold
VDD, falling edge (Note 3)
POR Threshold Hysteresis
Standby Supply Current
VDD = 3.3 V, No SMBus Activity
SCLK at 10 kHz
−
−
1.0
4.0
5.0
−
mA
Average Operating Supply Current
0.25 Conversions/Sec Rate
−
130
200
mA
Auto−convert Mode, Averaged Over 4 Sec
2 Conversions/Sec Rate
−
225
370
mA
Conversion Time
From Stop Bit to Conversion Complete
(Both Channels) D+ Forced to D− + 0.65 V
65
115
170
ms
Remote Sensor Source Current
High Level (Note 3)
Low Level (Note 3)
120
7.0
205
12
300
16
mA
−
0.7
−
V
−
50
−
mA
D− Source Voltage
Address Pin Bias Current (ADD0, ADD1)
Momentary at Power-on Reset
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ADM1021A
Table 4. ELECTRICAL CHARACTERISTICS (continued)
(TA = TMIN to TMAX, VDD = 3.0 V to 3.6 V, unless otherwise noted) (Note 1)
Parameter
Test Conditions/Comments
Min
Typ
Max
Unit
SMBus Interface (See Figure 2)
Logic Input High Voltage, VIH
STBY, SCLK, SDATA
VDD = 3.0 V to 5.5 V
2.2
−
−
V
Logic Input Low Voltage, VIL
STBY, SCLK, SDATA
VDD = 3.0 V to 5.5 V
−
−
0.8
V
SMBus Output Low Sink Current
SDATA Forced to 0.6 V
6.0
−
−
mA
ALERT Output Low Sink Current
ALERT Forced to 0.4 V
1.0
−
−
mA
−1.0
−
+1.0
mA
SMBus Input Capacitance, SCLK, SDATA
−
5.0
−
pF
SMBus Clock Frequency
−
−
100
kHz
Logic Input Current, IIH, IIL
SMBus Clock Low Time, tLOW
tLOW between 10% Points
4.7
−
−
ms
SMBus Clock High Time, tHIGH
tHIGH between 90% Points
4.0
−
−
ms
4.7
−
−
ms
SMBus Start Condition Setup Time,
tSU:STA
SMBus Repeat Start Condition
250
−
−
ns
Setup Time, tSU:STA
Between 90% and 90% Points
250
−
−
ns
SMBus Start Condition Hold Time, tHD:STA
Time from 10% of SDATA to 90% of SCLK
4.0
−
−
ms
SMBus Stop Condition Setup Time, tSU:STO
Time from 90% of SCLK to 10% of SDATA
4.0
−
−
ms
SMBus Data Valid to SCLK
Time for 10% or 90% of SDATA to 10% of SCLK
250
−
−
ns
Rising Edge Time, tSU:DAT
Time for 10% or 90% of SDATA to 10% of SCLK
250
−
−
ns
0
−
−
ms
Between Start/Stop Condition
4.7
−
−
ms
−
−
1
ms
−
−
1
ms
SMBus Data Hold Time, tBUF:DAT
SMBus Bus Free Time, tBUF
SCLK Falling Edge to SDATA
Valid Time, tVD:DAT
Master Clocking in Data
1. TMAX = 100C, TMIN = 0C
2. Operation at VDD = 5.0 V guaranteed by design; not production tested.
3. Guaranteed by design; not production tested.
t LOW
tF
t HD; STA
tR
SCLK
t HD; STA
t HD; DAT
t HIGH
t SU; STA
t SU; DAT
t SU; STO
SDATA
t BUF
STOP START
START
Figure 2. Serial Bus Timing
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STOP
ADM1021A
TYPICAL PERFORMANCE CHARACTERISTICS
5
15
TEMPERATURE ERROR (C)
TEMPERATURE ERROR (C)
20
10
D+ To GND
5
0
−5
D+ To VDD
−10
−15
−20
−25
−30
1
10
4
250 mV p-p REMOTE
3
2
100 mV p-p REMOTE
1
0
100
100
1k
LEAKAGE RESISTANCE (MW)
TEMPERATURE ERROR (C)
TEMPERATURE ERROR (C)
6
5
4
50 mV p-p
2
1
0
25 mV p-p
1
10
100
1k
10k 100k
1M
UPPER SPEC LEVEL
1
DEV10
0
−1
LOWER SPEC LEVEL
−2
−3
50
10M 100M
60
70
12
60
SUPPLY CURRENT (mA)
TEMPERATURE ERROR (C)
70
10
8
6
4
2
100
110
120
50
40
30
10
−2
0
10 12 14 16 18 20 22 24
VDD = 3.3 V
20
0
8
90
Figure 6. Temperature Error vs. Pentium) III
Temperature
14
6
80
TEMPERATURE (C)
Figure 5. Temperature Error vs. Common-mode
Noise Frequency
4
100M
2
FREQUENCY (Hz)
2
10M
3
7
3
1M
Figure 4. Temperature Error vs. Power Supply
Noise Frequency
100 mV p-p
8
100k
FREQUENCY (Hz)
Figure 3. Temperature Error vs. PC Board Track
Resistance
9
10k
VDD = 5 V
1
5
10
25
50
75 100 250 500 750 1000
SCLK FREQUENCY (kHz)
CAPACITANCE (nF)
Figure 7. Temperature Error vs. Capacitance
between D+ and D−
Figure 8. Standby Supply Current vs. Clock
Frequency
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ADM1021A
TYPICAL PERFORMANCE CHARACTERISTICS (Cont’d)
550
500
SUPPLY CURRENT (mA)
TEMPERATURE ERROR (C)
4
3
10 mV p-p
2
1
450
400
350
300
250
200
3.3 V
150
100
0
100k
1M
10M
100M
5V
50
0.0625 0.125
1G
Figure 9. Temperature Error vs. Differential-mode
Noise Frequency
1
2
4
8
Figure 10. Operating Supply Current
vs. Conversion Rate
100
125
80
REMOTE
TEPMERATURE
100
TEMPERATURE (C)
SUPPLY CURRENT (mA)
0.5
CONVERTION RATE (Hz)
FREQUENCY (Hz)
60
40
20
INT TEPMERATURE
75
50
25
0
−20
0.25
0
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
0
1
2
3
4
5
6
7
8
9
TIME (s)
SUPPLY VOLTAGE (V)
Figure 11. Standby Supply Current vs. Supply
Voltage
Figure 12. Response to Thermal Shock
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10
ADM1021A
Functional Description
On initial powerup, 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 output. This
can 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 works only if the measured values are within
the limit values.
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 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 (SMBus). 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
I
NI
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 the effect of the absolute value of VBE, which varies
from device to device.
IBIAS
VDD
D+
REMOTE
SENSING
TRANSISTOR
VOUT+
To ADC
C1*
D−
VOUT−
BIAS
DIODE
LOW-PASS FILTER
fC = 65 kHz
*CAPACITOR C1 IS OPTIONAL. IT IS ONLY NECESSARY IN NOISY ENVIRONMENTS.
C1 = 2.2 nF TYP, 3 nF MAX
Figure 13. Input Signal Conditioning
This figure shows the external sensor as a substrate
transistor provided for temperature monitoring on some
microprocessors, but it could 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, one can
optionally be added as a noise filter. Its value is typically
2,200 pF, but it should be no more than 3,000 pF. See the
Layout Considerations section for more information.
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:
DV BE + kTńq
1n (N)
(eq. 1)
where:
k is Boltzmann’s constant.
q is the charge on the electron (1.6  10–19 Coulombs).
T is the absolute temperature in Kelvins.
N is the ratio of the two currents.
Figure 13 shows the input signal conditioning used to
measure the output of an external temperature sensor.
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ADM1021A
Temperature Data Format
To measure DVBE, the sensor is switched between
operating currents of I and N  I. The resulting waveform is
passed through a 65 kHz low-pass filter to remove noise, and
then to a chopper-stabilized amplifier that performs the
functions of amplification and rectification of the waveform
to produce a dc voltage proportional to DVBE. This 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.
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; therefore,
the actual range is 0C to 127C. The temperature data
format is shown in Table 5.
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 5. TEMPERATURE DATA FORMAT
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 mA vs. 90 mA for the ADM1021. The primary
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 vs. 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 to 0C in the ADM1021. As the part
is powered up converting (except when the part is
in standby mode, that is, Pin 15 is pulled low), the
part measures the actual values of remote and local
temperature and writes these to the registers.
5. The four MSBs of the revision register can be used
to identify the part. The ADM1021 revision register
reads 0x0x, and the ADM1021A reads 0x3x.
6. The power-on default value of the address pointer
register is undefined in the ADM1021A and is
equal to 0x00 in the ADM1021. As a result, a
value must be written to the address pointer
register before a read is performed 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 powerup.
7. Setting the mask bit (Bit 7 Config Reg) on the
ADM1021A masks current and future ALERTs.
On the ADM1021, the mask bit, masks only
ALERTs. Any current ALERT has to be cleared
using an ARA.
Temperature (5C)
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
Registers
The ADM1021A contains nine registers that are used to
store the results of remote and local temperature
measurements, and high and low temperature limits, and to
configure and control the device. A description of these
registers follows, and further details are given in Table 6 to
Table 8. 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, produces an invalid result. Register
addresses above 0x0F are reserved for future use or used for
factory test purposes and should not be written to.
Address Pointer Register
The address pointer register does not have and does not
require an address, because 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. Bit 5 to Bit 3 are flags that indicate
the results of the limit comparisons.
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ADM1021A
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 are 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 is set and the ALERT output goes low. Reading
the status register clears 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 6. STATUS REGISTER BIT ASSIGNMENTS
Bit
Name
7
BUSY
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 to 0
Function
1 when ADC Converting
Reserved
*These flags stay high until the status register is read or they are
reset by POR.
Table 7. 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 Temperature Value
1000 0000 (0x80) (−128C)
01
Not Applicable
Remote Temperature Value
1000 0000 (0x80) (−128C)
02
Not Applicable
Status
Undefined
03
09
Configuration
0000 0000 (0x00)
04
0A
Conversion Rate
0000 0010 (0x02)
05
0B
Local Temperature High Limit
0111 1111 (0x7F) (+127C)
06
0C
Local Temperature Low Limit
1100 1001 (0xC9) (−55C)
07
0D
Remote Temperature High
Limit
0111 1111 (0x7F) (+127C)
08
0E
Remote Temperature Low
Limit
1100 1001 (0xC9) (−55C)
Not Applicable
0F (Note 1)
One-shot
10
Not Applicable
Reserved
Reserved for Future Versions
11
11
Remote Temperature Offset
0000 0000 (0C)
12
12
Reserved
Reserved for Future Versions
13
13
Reserved
Reserved for Future Versions
14
14
Reserved
Reserved for Future Versions
15
16
Reserved
Reserved for Future Versions
17
18
Reserved
Reserved for Future Versions
19
Not Applicable
Reserved
Reserved for Future Versions
20
21
Reserved
Reserved for Future Versions
FE
Not Applicable
Manufacturer Device ID
0100 0001 (0x41)
FF
Not Applicable
Die Revision Code
0011 xxxx (0x3x)
1. Writing to Address 0F causes the ADM1021A to perform a single measurement. It is not a data register and data written to it is irrelevant.
The ALERT interrupt latch is not reset by reading the
status register, but is reset when the ALERT output is
serviced by the master reading the device address, provided
the error condition has gone away and the status register flag
bits have been reset.
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 values they were when
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.
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
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ADM1021A
and PCB track resistance. See Table 10 for an example of
offset values.
The offset value is stored as an 8-bit, twos complement
value. The value of the offset is negative if the MSB of
Register 0x11 is 1, and is positive if the MSB of
Register 0x11 is 0. This value is added to the remote
temperature. The offset register defaults to 0 at powerup.
The offset register range is −128C to +127C.
Table 8. CONFIGURATION REGISTER BIT
ASSIGNMENTS
Power-on
Default
Bit
Name
Function
7
MASK1
0 = ALERT Enabled
1 = ALERT Masked
0
6
RUN/STOP
0 = Run
1 = Standby
0
Reserved
0
5 to 0
Table 10. OFFSET VALUES
Offset Register
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 0x07) to 16 seconds (Code 0x00). 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 0. Use of
slower conversion times greatly reduces the device power
consumption, as shown in Table 9.
Remote Temperature
(0x11)
Offset
Value
(With
Offset)
(Without
Offset)
1111 1100
−4C
14C
18C
1111 1111
−1C
17C
18C
0000 0000
0C
18C
18C
0000 0001
+1C
19C
18C
0000 0100
+4C
22C
18C
One-shot Register
Table 9. CONVERSION RATE REGISTER CODE
Data
Conversion/
Sec
Average Supply Current
mA Typ at VCC = 3.3 V
0x00
0.0625
150
0x01
0.125
150
0x02
0.25
150
0x03
0.5
150
0x04
1
150
0x05
2
150
0x06
4
160
0x07
8
180
0x08 to 0xFF
Reserved
−
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 one-shot 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
Limit Registers
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 responds.
The ADM1021A has two address pins, ADD0 and ADD1,
to allow selection of the device address so that several
ADM1021A’s 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 VDD so that a total of nine different
addresses are possible, as shown in Table 11.
It should be noted that the state of the address pins is only
sampled at powerup, so changing them after powerup has no
effect.
The ADM1021A has four limit registers to store local and
remote and 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 results in an alarm condition. Even though the
temperature measurement range is from 0 to 127C, it is
possible to program the limit register with negative values.
This is for backwards compatibility with the ADM1021.
Offset Register
An offset register is provided at Address 0x11. This
allows the user to remove errors from the measured remote
temperature. These errors can be introduced by clock noise
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10
ADM1021A
low period of the clock signal and remain stable
during the high period, because a low-to-high
transition when the clock is high can 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 pulls the data line high during the 10th
clock pulse to assert a stop condition. In read
mode, the master device overrides 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
then takes 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.
Table 11. DEVICE ADDRESSES (Note 1)
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
1. ADD0 and ADD1 are sampled at powerup 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, that is, 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 writes
to the slave device. If the R/W bit is a 1, the
master reads 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
1
Any number of bytes of data can 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.
For 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.
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.
9
9
1
SCLK
SDATA
START BY
MASTER
A6
A5
A4
A3
A2
A1
A0
FRAME 1
SERIAL BUS ADDRESS BYTE
R/W
D7
D6
D5
D4
D3
D2
D1
D0
ACK. BY
ADM1021A
FRAME 2
ADDRESS POINTER REGISTER BYTE
ACK. BY
ADM1021A
1
9
SCLK (CONTINUED)
SDATA (CONTINUED)
D7
D6
D5
D4
D3
D2
FRAME 3
DATA BYTE
D1
D0
ACK. BY STOP BY
ADM1021A MASTER
Figure 14. Writing a Register Address to the Address Pointer Register, then Writing Data to the Selected Register
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11
ADM1021A
1
9
9
1
SCLK
SDATA
A6
START BY
MASTER
A5
A4
A3
A2
A1
A0
FRAME 1
SERIAL BUS ADDRESS BYTE
D7
R/W
ACK. BY
ADM1021A
D6
D5
D4
D3
D2
D1
D0
ACK. BY
ADM1021A
FRAME 2
ADDRESS POINTER REGISTER BYTE
STOP BY
MASTER
Figure 15. Writing to the Address Pointer Register Only
9
1
1
9
SCLK
SDATA
A6
START BY
MASTER
A5
A4
A0 R/W
D7
ACK. BY
ADM1021A
FRAME 1
SERIAL BUS ADDRESS BYTE
A3
A2
A1
D6
D5
D4
D3
D2
D1
D0
NO ACK. BY
MASTER
FRAME 2
DATA BYTE FROM ADM1021A
STOP BY
MASTER
Figure 16. Reading Data from a Previously Selected Register
ALERT Output
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, because 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 16.
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 15
can be omitted.
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 kW
pullup to VDD. Several ALERT outputs can be wire-ANDed
together so the common line goes 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 can be used as an SMBALERT. Slave devices
on the SMBus cannot normally 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 shown in Figure 17.
MASTER RECEIVES SMBALERT
START
ALERT RESPONSE
ADDRESS
MASTER SENDS
ARA AND READ
COMMAND
NOTES: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; this is because the first data
byte of a write is always written to the address pointer
register.
RD ACK
DEVICE
ADDRESS
NO
STOP
ACK
DEVICE SENDS
ITS ADDRESS
Figure 17. Use of SMBALERT
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 has priority,
in accordance with normal SMBus arbitration.
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.
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12
ADM1021A
Factors Affecting Accuracy
5. Once the ADM1021A has responded to the alert
response address, it resets its ALERT output,
provided that the error condition that caused the
ALERT no longer exists. If the SMBALERT line
remains low, the master sends the ARA again, and
so on until all devices whose ALERT outputs were
low have responded.
Remote Sensing Diode
The ADM1021A is designed to work with substrate
transistors built into processors, or with discrete transistors.
Substrate transistors are generally 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 is
obtained by choosing devices according to the following
criteria:
1. Base-emitter voltage greater than 0.25 V at 6 mA,
at the highest operating temperature.
2. Base-emitter voltage less than 0.95 V at 100 mA, at
the lowest operating temperature.
3. Base resistance less than 100 W.
4. Small variation in hFE (such as 50 to 150), which
indicates tight control of VBE characteristics.
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 mA if there is no
SMBus activity or 100 mA 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 0xXX to the one-shot
register (Address 0x0F).
Transistors, such as 2N3904, 2N3906, or equivalents, in
SOT−23 package are suitable devices to use.
Thermal Inertia and Self-heating
Sensor Fault Detection
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 causes a lag in the
response of the sensor to a temperature change. For the
remote sensor, this should not be a problem, because it is
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 is, however, often remote from the
processor and only monitors the general ambient
temperature around the package. The thermal time constant
of the QSOP−16 package is approximately 10 seconds.
In practice, the package will have an electrical, and hence
a thermal, connection to the printed circuit board, so the
temperature rise due to self-heating is negligible.
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 VCC – 1.0 V (typical). The output of this
comparator is checked 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 outputs −128C (1000 0000).
Since the normal operating temperature range of the device
only extends down to 0C, this output code is never seen in
normal operation; therefore, it can be interpreted as a fault
condition.
In this respect, the ADM1021A differs from and improves
upon competitive devices that output 0 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 can be cleared by writing
0x80 (−128C) to the low limit register.
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13
ADM1021A
Layout Considerations
7. For very 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.
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, ensure 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 mV, and
thermocouple voltages are about 3 mV/C of
temperature difference. Unless there are two
thermocouples with a big temperature differential
between them, thermocouple voltages should be
much less than 240 mV.
5. Place a 0.1 mF bypass capacitor close to the VDD
pin, and 2,200 pF input filter capacitors across D+,
D− close to the ADM1021A.
6. If the distance to the remote sensor is more than
eight inches, the use of twisted pair cable is
recommended. This works up to about 6 to 12 feet.
GND
10 MIL
10 MIL
D+
10 MIL
10 MIL
10 MIL
D−
10 MIL
GND
10 MIL
Figure 18. Arrangement of Signal Tracks
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 can be reduced or removed.
Cable resistance can also introduce errors. A series
resistance of 1 W introduces about 1C error.
Application Circuits
Figure 19 shows a typical application circuit for the
ADM1021A, using a discrete sensor transistor connected
via a shielded, twisted pair cable. The pullups 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 ADM1021A can be
interfaced directly to the SMBus of an I/O chip. Figure 20
shows how the ADM1021A might be integrated into a
system using this type of I/O controller.
ADM1021A
VDD
3.3 V
0.1 mF
STBY
SCLK
IN
SDATA
I/O
ALERT
OUT
D+
C1*
D−
2N3904
ALL 10 kW
SHIELD
ADD0
SET TO REQUIRED
ADDRESS
ADD1
GND
* C1 IS OPTIONAL
Figure 19. Typical Application Circuit
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14
TO CONTROL
CHIP
ADM1021A
PROCESSOR
D−
D+
ADM1021A
SYSTEM BUS
ALERT
SDATA
SCLK
SYSTEM
MEMORY
DISPLAY
GMCH
DISPLAY
CACHE
CD−ROM
PCI SLOTS
HARD
DISK
2 IDE PORTS
USB
ICH
I/O CONTROLLER
HUB
PCI BUS
SMBus
SUPER
I/O
USB
2 USB PORTS
FWH
(FIREWARE HUB)
Figure 20. Typical System Using ADM1021A
Table 12. ORDERING INFORMATION
Device Number*
ADM1021AARQZ−R
Temperature Range
Package Type
Package Option
Shipping†
0C to +100C
16-lead QSOP
RQ−16
2,500 Tape & Reel
†For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging
Specifications Brochure, BRD8011/D.
*The “Z’’ suffix indicates Pb-Free part.
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15
ADM1021A
PACKAGE DIMENSIONS
QSOP16
CASE 492−01
ISSUE A
2X
NOTES:
1. DIMENSIONING AND TOLERANCING PER ASME
Y14.5M, 1994.
2. CONTROLLING DIMENSION: MILLIMETERS.
3. DIMENSION b DOES NOT INCLUDE DAMBAR
PROTRUSION.
4. DIMENSION D DOES NOT INCLUDE MOLD FLASH,
PROTRUSIONS, OR GATE BURRS. MOLD FLASH,
PROTRUSIONS, OR GATE BURRS SHALL NOT EX­
CEED 0.005 PER SIDE. DIMENSION E1 DOES NOT
INCLUDE INTERLEAD FLASH OR PROTRUSION. IN­
TERLEAD FLASH OR PROTRUSION SHALL NOT EX­
CEED 0.005 PER SIDE. D AND E1 ARE DETERMINED
AT DATUM H.
5. DATUMS A AND B ARE DETERMINED AT DATUM H.
0.20 C D
D
16
L2
D
A
9
GAUGE
PLANE
SEATING
PLANE
E
E1
C
L
C
DETAIL A
2X
2X 10 TIPS
0.20 C D
1
8
16X
e
B
A2
0.10 C
0.10 C
16X
b
0.25
A1
C
DIM
A
A1
A2
b
c
D
E
E1
e
h
L
L2
M
0.25 C D
M
C A-B D
h x 45 _
H
A
SEATING
PLANE
DETAIL A
M
INCHES
MIN
MAX
0.053
0.069
0.004
0.010
0.049
---0.008
0.012
0.007
0.010
0.193 BSC
0.237 BSC
0.154 BSC
0.025 BSC
0.009
0.020
0.016
0.050
0.010 BSC
0_
8_
MILLIMETERS
MIN
MAX
1.35
1.75
0.10
0.25
1.24
---0.20
0.30
0.19
0.25
4.89 BSC
6.00 BSC
3.90 BSC
0.635 BSC
0.22
0.50
0.40
1.27
0.25 BSC
0_
8_
SOLDERING FOOTPRINT*
16X
16X
0.42
16
1.12
9
6.40
1
8
0.635
PITCH
DIMENSIONS: MILLIMETERS
*For additional information on our Pb-Free strategy and soldering
details, please download the ON Semiconductor Soldering and
Mounting Techniques Reference Manual, SOLDERRM/D.
Pentium is a registered trademark of Intel Corporation.
ON Semiconductor and
are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC owns the rights to a number of patents, trademarks,
copyrights, trade secrets, and other intellectual property. A listing of SCILLC’s product/patent coverage may be accessed at www.onsemi.com/site/pdf/Patent−Marking.pdf. SCILLC
reserves the right to make changes without further notice to any products herein. SCILLC makes no warranty, representation or guarantee regarding the suitability of its products for any
particular purpose, nor does SCILLC assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without
limitation special, consequential or incidental damages. “Typical” parameters which may be provided in SCILLC data sheets and/or specifications can and do vary in different applications
and actual performance may vary over time. All operating parameters, including “Typicals” must be validated for each customer application by customer’s technical experts. SCILLC
does not convey any license under its patent rights nor the rights of others. SCILLC products are not designed, intended, or authorized for use as components in systems intended for
surgical implant into the body, or other applications intended to support or sustain life, or for any other application in which the failure of the SCILLC product could create a situation where
personal injury or death may occur. Should Buyer purchase or use SCILLC products for any such unintended or unauthorized application, Buyer shall indemnify and hold SCILLC and
its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly,
any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that SCILLC was negligent regarding the design or manufacture
of the part. SCILLC is an Equal Opportunity/Affirmative Action Employer. This literature is subject to all applicable copyright laws and is not for resale in any manner.
PUBLICATION ORDERING INFORMATION
LITERATURE FULFILLMENT:
Literature Distribution Center for ON Semiconductor
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Phone: 303−675−2175 or 800−344−3860 Toll Free USA/Canada
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16
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For additional information, please contact your local
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ADM1021A/D
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