MAX1805MEE-T [MAXIM]
Serial Switch/Digital Sensor, 8 Bit(s), 3Cel, Rectangular, 16 Pin, Surface Mount, 0.150 INCH, QSOP-16;
| 型号： | MAX1805MEE-T |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Serial Switch/Digital Sensor, 8 Bit(s), 3Cel, Rectangular, 16 Pin, Surface Mount, 0.150 INCH, QSOP-16 输出元件 传感器 换能器 |
| 文件： | 总17页 (文件大小：279K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-1766; Rev 2; 5/03
Multichannel Remote/Local
Temperature Sensors
________________General Description
____________________________Features
The MAX1668/MAX1805/MAX1989 are precise multi-
channel digital thermometers that report the tempera-
ture of all remote sensors and their own packages. The
remote sensors are diode-connected transistors—typi-
cally low-cost, easily mounted 2N3904 NPN types—that
replace conventional thermistors or thermocouples.
Remote accuracy is 3ꢀ° for multiple transistor manu-
facturers, with no calibration needed. The remote chan-
nels can also measure the die temperature of other I°s,
such as microprocessors, that contain an on-chip,
diode-connected transistor.
ꢀ Multichannel
4 Remote, 1 Local (MAX1668/MAX1989)
2 Remote, 1 Local (MAX1805)
ꢀ No Calibration Required
ꢀ SMBus 2-Wire Serial Interface
ꢀ Programmable Under/Overtemperature Alarms
ꢀ Supports SMBus Alert Response
ꢀ Accuracy
±2ꢀC (ꢁ60ꢀC to ꢁ100ꢀC, Local)
±±ꢀC (-40ꢀC to ꢁ125ꢀC, Local)
±±ꢀC (ꢁ60ꢀC to ꢁ100ꢀC, Remote)
The 2-wire serial interface accepts standard system
management bus (SMBus™) write byte, read byte, send
byte, and receive byte commands to program the alarm
thresholds and to read temperature data. The data for-
mat is 7 bits plus sign, with each bit corresponding to
1ꢀ°, in two’s-complement format.
ꢀ ±µA (typ) Standby Supply Current
ꢀ 700µA (max) Supply Current
The MAX1668/MAX1805/MAX1989 are available in
small, 16-pin QSOP surface-mount packages. The
MAX1989 is also available in a 16-pin TSSOP.
ꢀ Small, 16-Pin QSOP/TSSOP Packages
_______________Ordering Information
________________________Applications
PART
TEMP RANGE
-55ꢀ° to +125ꢀ°
-55ꢀ° to +125ꢀ°
-55ꢀ° to +125ꢀ°
-55ꢀ° to +125ꢀ°
PIN-PACKAGE
16 QSOP
MAX1668MEE
MAX1805MEE
MAX1989MEE
MAX1989MUE
Desktop and Notebook
°omputers
°entral-Office Telecom
Equipment
16 QSOP
16 QSOP
LAN Servers
Test and Measurement
Multichip Modules
16 TSSOP
Industrial °ontrols
Pin Configuration
Typical Operating Circuit
3V TO 5.5V
0.1µF
200Ω
TOP VIEW
DXP1
DXN1
1
2
3
4
5
6
7
8
16 GND
V
STBY
CC
10kΩ EACH
15 STBY
14 SMBCLK
MAX1668
MAX1805
MAX1989
DXP2
DXP1
CLOCK
DATA
SMBCLK
DXN2
MAX1668
13 SMBDATA
12 ALERT
11 ADD0
2200pF
MAX1805
MAX1989
SMBDATA
ALERT
(N.C.) DXP3
(N.C.) DXN3
(N.C.) DXP4
(N.C.) DXN4
DXN1
*
INTERRUPT
TO µC
10 ADD1
DXP4
DXN4
2200pF
9
V
CC
*
ADD0 ADD1 GND
QSOP/TSSOP
( ) ARE FOR MAX1805.
*
DIODE-CONNECTED TRANSISTOR
SMBus is a trademark of Intel Corp.
†Patents Pending
________________________________________________________________ Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
Multichannel Remote/Local
Temperature Sensors
ABSOLUTE MAXIMUM RATINGS
°°
DXP_, ADD_, STBY to GND........................-0.3V to (V
DXN_ to GND ........................................................-0.3V to +0.8V
SMB°LK, SMBDATA, ALERT to GND......................-0.3V to +6V
SMBDATA, ALERT °urrent .................................-1mA to +50mA
DXN_ °urrent...................................................................... 1mA
V
to GND..............................................................-0.3V to +6V
Operating Temperature Range .........................-55ꢀ° to +125ꢀ°
Junction Temperature......................................................+150ꢀ°
Storage Temperature Range.............................-65ꢀ° to +150ꢀ°
Lead Temperature (soldering, 10s) .................................+300ꢀ°
+ 0.3V)
°°
°ontinuous Power Dissipation (T = +70ꢀ°)
A
QSOP (derate 8.30mW/ꢀ° above +70ꢀ°)....................667mW
TSSOP (derate 9.40mW/ꢀ° above +70ꢀ°) ..................755mW
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(V
= +3.3V, STBY = V , configuration byte = X0XXXX00, T = 0ꢀC to +125ꢀC, unless otherwise noted.)
°°
A
°°
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
ADC AND POWER SUPPLY
Temperature Resolution (Note 1)
Monotonicity guaranteed
T = +60ꢀ° to +100ꢀ°
8
-2
Bits
ꢀ°
+2
+3
A
Initial Temperature Error,
Local Diode (Note 2)
T = 0ꢀ° to +125ꢀ°
A
-3
T = +60ꢀ° to +100ꢀ°
-3
+3
R
Temperature Error, Remote Diode
(Notes 2, 3)
ꢀ°
ꢀ°
T = -55ꢀ° to +125ꢀ°
R
-5
+5
T = +60ꢀ° to +100ꢀ°
-2.5
-3.5
3.0
2.60
+2.5
+3.5
5.5
A
Temperature Error, Local Diode
(Notes 1, 2)
Including long-term drift
T = 0ꢀ° to +85ꢀ°
A
Supply Voltage Range
V
V
Undervoltage Lockout Threshold
Undervoltage Lockout Hysteresis
Power-On Reset (POR) Threshold
POR Threshold Hysteresis
V
V
input, disables A/D conversion, rising edge
2.8
50
2.95
°°
mV
V
, falling edge
1.3
1.8
50
2.3
°°
mV
SMBus static
3
5
10
12
Logic inputs
Standby Supply °urrent
forced to V
or GND
µA
°°
Hardware or software standby,
SMB°LK at 10kHz
Average measured over 4s; logic inputs forced
or GND
Average Operating Supply °urrent
°onversion Time
400
700
µA
ms
V
°°
From stop bit to conversion complete (all channels)
High level (POR state)
260
70
7
320
100
10
380
130
13
Low level (POR state)
°onfiguration byte =
DXP_ forced to 1.5V
Remote-Diode Source °urrent
200
50
µA
X0XXXX10, high level
°onfiguration byte =
X0XXXX01, high level
DXN_ Source Voltage
0.7
V
Address Pin Bias °urrent
ADD0, ADD1; momentary upon power-on reset
160
µA
2
_______________________________________________________________________________________
Multichannel Remote/Local
Temperature Sensors
ELECTRICAL CHARACTERISTICS (continued)
(V
= +3.3V, STBY = V , configuration byte = X0XXXX00, T = 0ꢀC to +125ꢀC, unless otherwise noted.)
°°
A
°°
PARAMETER
SMBus INTERFACE
CONDITIONS
MIN
TYP
MAX
UNITS
Logic Input High Voltage
Logic Input Low Voltage
Logic Output Low Sink °urrent
2.2
V
V
STBY, SMB°LK, SMBDATA; V
= 3V to 5.5V
°°
0.8
STBY, SMB°LK, SMBDATA; V
= 3V to 5.5V
°°
6
mA
ALERT, SMBDATA forced to 0.4V
ALERT forced to 5.5V
ALERT Output High Leakage
°urrent
1
µA
Logic Input °urrent
Logic inputs forced to V
SMB°LK, SMBDATA
(Note 4)
or GND
-1
+1
µA
pF
kHz
µs
°°
SMBus Input °apacitance
SMBus °lock Frequency
SMB°LK °lock Low Time
SMB°LK °lock High Time
SMBus Start-°ondition Setup Time
5
D°
4.7
4
100
t , 10% to 10% points
LOW
t , 90% to 90% points
HIGH
µs
4.7
µs
SMBus Repeated Start-°ondition
Setup Time
t , 90% to 90% points
SU:STA
250
ns
SMBus Start-°ondition Hold Time
SMBus Stop-°ondition Setup Time
t
t
, 10% of SMBDATA to 90% of SMB°LK
, 90% of SMB°LK to 10% of SMBDATA
4
4
µs
µs
HD:STA
SU:STO
SMBus Data Valid to SMB°LK
Rising-Edge Time
t
t
, 10% or 90% of SMBDATA to 10% of SMB°LK
, slave receive (Note 5)
250
0
ns
ns
µs
SU:DAT
SMBus Data-Hold Time
HD:DAT
SMB°LK Falling Edge to SMBus
Data-Valid Time
Master clocking in data
1
ELECTRICAL CHARACTERISTICS
(V
= +5V, STBY = V , configuration byte = X0XXXX00, T = -55ꢀC to +125ꢀC, unless otherwise noted.) (Note 6)
°°
A
°°
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
ADC AND POWER SUPPLY
Temperature Resolution
Monotonicity guaranteed
8
-2
Bits
ꢀ°
T
A
T
A
T
R
T
R
= +60ꢀ° to +100ꢀ°
+2
+3
Initial Temperature Error,
Local Diode (Note 2)
= -55ꢀ° to +125ꢀ°
= +60ꢀ° to +100ꢀ°
= -55ꢀ° to +125ꢀ°
-3
-3
+3
Temperature Error, Remote Diode
(Notes 2, 3)
ꢀ°
-5
+5
Supply-Voltage Range
°onversion Time
4.5
260
5.5
380
V
From stop bit to conversion complete (both channels)
ms
_______________________________________________________________________________________
3
Multichannel Remote/Local
Temperature Sensors
ELECTRICAL CHARACTERISTICS (continued)
(V
= +5V, STBY = V , configuration byte = X0XXXX00, T = -55ꢀC to +125ꢀC, unless otherwise noted.) (Note 6)
°°
A
°°
PARAMETER
CONDITIONS
MIN
2.4
6
TYP
MAX
UNITS
SMBus INTERFACE
Logic Input High Voltage
Logic Input Low Voltage
Logic Output Low Sink °urrent
V
V
STBY, SMB°LK, SMBDATA; V
= 4.5V to 5.5V
°°
0.8
STBY, SMB°LK, SMBDATA; V
= 4.5V to 5.5V
°°
mA
ALERT, SMBDATA forced to 0.4V
ALERT Output High Leakage
°urrent
1
µA
µA
ALERT forced to 5.5V
Logic Input °urrent
Logic inputs forced to V
or GND
-2
+2
°°
Note 1: Guaranteed by design, but not production tested.
Note 2: Quantization error is not included in specifications for temperature accuracy. For example, if the MAX1668/MAX1805/
MAX1989 device temperature is exactly +66.7ꢀ°, the AD° may report +66ꢀ°, +67ꢀ°, or +68ꢀ° (due to the quantization
error plus the +0.5ꢀ° offset used for rounding up) and still be within the guaranteed 1ꢀ° error limits for the +60ꢀ° to
+100ꢀ° temperature range. See Table 2.
Note 3: A remote diode is any diode-connected transistor from Table 1. T is the junction temperature of the remote diode. See the
R
Remote-Diode Selection section for remote-diode forward-voltage requirements.
Note 4: The SMBus logic block is a static design that works with clock frequencies down to D°. While slow operation is possible, it
violates the 10kHz minimum clock frequency and SMBus specifications, and can monopolize the bus.
Note 5: Note that a transition must internally provide at least a hold time in order to bridge the undefined region (300ns max) of
SMB°LK’s falling edge t
HD:DAT.
Note 6: Specifications from -55ꢀ° to +125ꢀ° are guaranteed by design, not production tested.
Typical Operating Characteristics
(Typical Operating Circuit, V
= +5V, STBY = V , configuration byte = X0XXXX00, T = +25ꢀ°, unless otherwise noted.)
°° A
°°
TEMPERATURE ERROR
vs. TEMPERATURE
TEMPERATURE ERROR
vs. PC BOARD RESISTANCE
TEMPERATURE ERROR
vs. SUPPLY NOISE FREQUENCY
4
3
20
10
24
20
16
12
8
WITH V 0.1µF CAPACITOR REMOVED
CC
2200pF BETWEEN DXN_ AND DXP_
NPN (CMPT3904)
PNP (CMPT3906)
250mV
P-P
2
PATH = DXP_ TO GND
1
0
0
100mV
P-P
PATH = DXP_ TO V (5V)
CC
-10
-20
INTERNAL
-1
-2
4
0
-50 -30 -10 10 30 50 70 90 110
1
10
100
0.1
1
10
100
TEMPERATURE (°C)
LEAKAGE RESISTANCE (MΩ)
FREQUENCY (MHz)
4
_______________________________________________________________________________________
Multichannel Remote/Local
Temperature Sensors
Typical Operating Characteristics (continued)
(Typical Operating Circuit, V
= +5V, STBY = V , configuration byte = X0XXXX00, T = +25ꢀ°, unless otherwise noted.)
°°
°°
A
TEMPERATURE ERROR
vs. COMMON-MODE NOISE FREQUENCY
TEMPERATURE ERROR
vs. DXP_ TO DXN_ CAPACITANCE
STANDBY SUPPLY CURRENT
vs. CLOCK FREQUENCY
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
60
50
40
30
20
10
0
4
2
SQUARE-WAVE AC-COUPLED INTO DXN
2200pF BETWEEN DXN_ AND DXP_
STBY = GND
100mV
P-P
0
-2
-4
-6
-8
-10
50mV
P-P
V
CC
= 5V
V
= 3.3V
CC
0.1
1
10
100
1000
1
10
100
1000
0
10
20
30
40
50
60
FREQUENCY (MHz)
SMBCLK FREQUENCY (kHz)
DXP_ TO DXN_ CAPACITANCE (nF)
STANDBY SUPPLY CURRENT
vs. SUPPLY VOLTAGE
RESPONSE TO THERMAL SHOCK
160
140
120
100
80
125
100
75
50
25
0
STBY = GND
ADD0 = ADD1 = GND
60
40
ADD0 = ADD1 = HIGH-Z
16 QSOP IMMERSED IN
+115°C FLUORINERT BATH
20
0
0
1
2
3
4
5
-2
0
2
4
6
8
SUPPLY VOLTAGE (V)
TIME (s)
_______________________________________________________________________________________
5
Multichannel Remote/Local
Temperature Sensors
Pin Description
PIN
FUNCTION
MAX1668/
MAX1989
MAX1805
NAME
°ombined °urrent Source and A/D Positive Input for Remote-Diode °hannel. Do not
leave DXP floating; connect DXP to DXN if no remote diode is used. Place a 2200pF
capacitor between DXP and DXN for noise filtering.
1, 3, 5, 7
1, 3
DXP_
DXN_
°ombined °urrent Sink and A/D Negative Input. DXN is normally biased to a diode volt-
age above ground.
2, 4, 6, 8
9
2, 4
9
Supply Voltage Input, 3V to 5.5V. Bypass to GND with a 0.1µF capacitor. A 200Ω series
resistor is recommended but not required for additional noise filtering.
V
°°
SMBus Address Select Pin (Table 8). ADD0 and ADD1 are sampled upon power-up.
Excess capacitance (>50pF) at the address pins when floating can cause address-
recognition problems.
10
10
ADD1
11
12
13
14
11
12
13
14
ADD0
ALERT
SMBus Slave Address Select Pin
SMBus Alert (Interrupt) Output, Open Drain
SMBus Serial-Data Input/Output, Open Drain
SMBus Serial-°lock Input
SMBDATA
SMB°LK
Hardware Standby Input. Temperature and comparison threshold data are retained in
standby mode. Low = standby mode, high = operate mode.
15
15
STBY
16
—
16
GND
N.°.
Ground
5–8
No °onnection. Not internally connected. °an be used for P° board trace routing.
ADC and Multiplexer
_______________Detailed Description
The AD° is an averaging type that integrates over a
64ms period (each channel, typical), with excellent
noise rejection.
The MAX1668/MAX1805/MAX1989 are temperature
sensors designed to work in conjunction with an exter-
nal microcontroller (µ°) or other intelligence in thermo-
static, process-control, or monitoring applications. The
µ° is typically a power-management or keyboard con-
troller, generating SMBus serial commands by “bit-
banging” general-purpose input-output (GPIO) pins or
through a dedicated SMBus interface block.
The multiplexer automatically steers bias currents
through the remote and local diodes, measures their
forward voltages, and computes their temperatures.
Each channel is automatically converted once the con-
version process has started. If any one of the channels
is not used, the device still performs measurements on
these channels, and the user can ignore the results of
the unused channel. If any remote-diode channel is
unused, connect DXP_ to DXN_ rather than leaving the
pins open.
These devices are essentially 8-bit serial analog-to-digi-
tal converters (AD°s) with sophisticated front ends.
However, the MAX1668/MAX1805/MAX1989 also contain
a switched current source, a multiplexer, an AD°, an
SMBus interface, and associated control logic (Figure 1).
In the MAX1668 and MAX1989, temperature data from
the AD° is loaded into five data registers, where it is
automatically compared with data previously stored in
10 over/undertemperature alarm registers. In the
MAX1805, temperature data from the AD° is loaded into
three data registers, where it is automatically compared
with data previously stored in six over/undertemperature
alarm registers.
The DXN_ input is biased at 0.65V above ground by an
internal diode to set up the A/D inputs for a differential
measurement. The worst-case DXP_ to DXN_ differential
input voltage range is 0.25V to 0.95V.
Excess resistance in series with the remote diode caus-
es about +0.5ꢀ° error per ohm. Likewise, 200µV of offset
voltage forced on DXP_ to DXN_ causes about 1ꢀ° error.
6
_______________________________________________________________________________________
Multichannel Remote/Local
Temperature Sensors
Figure 1. MAX1668/MAX1805/MAX1989 Functional Diagram
_______________________________________________________________________________________
7
Multichannel Remote/Local
Temperature Sensors
A/D Conversion Sequence
Table 1. Remote-Sensor Transistor
Manufacturers
If a start command is written (or generated automatically
in the free-running autoconvert mode), all channels are
converted, and the results of all measurements are
available after the end of conversion. A BUSY status bit
in the status byte shows that the device is actually per-
forming a new conversion; however, even if the AD° is
busy, the results of the previous conversion are always
available.
MANUFACTURER
MODEL NO.
°entral Semiconductor (USA)
Motorola (USA)
°MPT3904
MMBT3904
MMBT3904
SST3904
National Semiconductor (USA)
Rohm Semiconductor (Japan)
Samsung (Korea)
Remote-Diode Selection
Temperature accuracy depends on having a good-qual-
ity, diode-connected small-signal transistor. Accuracy
has been experimentally verified for all of the devices
listed in Table 1. The MAX1668/MAX1805/MAX1989 can
also directly measure the die temperature of °PUs and
other I°s having on-board temperature-sensing diodes.
KST3904-TF
SMBT3904
Siemens (Germany)
Zetex (England)
FMMT3904°T-ND
Note: Transistors must be diode connected (base shorted to
collector).
The transistor must be a small-signal type, either NPN
or PNP, with a relatively high forward voltage; other-
wise, the A/D input voltage range can be violated. The
forward voltage must be greater than 0.25V at 10µA;
check to ensure this is true at the highest expected
temperature. The forward voltage must be less than
0.95V at 100µA; check to ensure this is true at the low-
est expected temperature. Large power transistors do
not work at all. Also, ensure that the base resistance is
less than 100Ω. Tight specifications for forward-current
gain (+50 to +150, for example) indicate that the manu-
facturer has good process controls and that the
devices have consistent VBE characteristics.
worst-case error occurs when sinking maximum current
at the ALERT output. For example, with ALERT sinking
1mA, the typical power dissipation is V
x 400µA plus
°°
0.4V x 1mA. Package theta J-A is about 150ꢀ°/W, so
with V = 5V and no copper P° board heat sinking,
°°
the resulting temperature rise is:
dT = 2.4mW x 150ꢀ°/W = 0.36ꢀ°
Even with these contrived circumstances, it is difficult
to introduce significant self-heating errors.
ADC Noise Filtering
The AD° is an integrating type with inherently good
noise rejection, especially of low-frequency signals such
as 60Hz/120Hz power-supply hum. Micropower opera-
tion places constraints on high-frequency noise rejec-
tion; therefore, careful P° board layout and proper
external noise filtering are required for high-accuracy
remote measurements in electrically noisy environments.
For heat-sink mounting, the 500-32BT02-000 thermal
sensor from Fenwal Electronics is a good choice. This
device consists of a diode-connected transistor, an
aluminum plate with screw hole, and twisted-pair cable
(Fenwal Inc., Milford, MA, 508-478-6000).
Thermal Mass and Self-Heating
Thermal mass can seriously degrade the MAX1668/
MAX1805/MAX1989s’ effective accuracy. The thermal
time constant of the 16-pin QSOP package is about
140s in still air. For the MAX1668/MAX1805/MAX1989
junction temperature to settle to within +1ꢀ° after a
sudden +100ꢀ° change requires about five time con-
stants or 12 minutes. The use of smaller packages for
remote sensors, such as SOT23s, improves the situa-
tion. Take care to account for thermal gradients
between the heat source and the sensor, and ensure
that stray air currents across the sensor package do
not interfere with measurement accuracy.
High-frequency EMI is best filtered at DXP_ and DXN_
with an external 2200pF capacitor. This value can be
increased to about 3300pF (max), including cable
capacitance. Higher capacitance than 3300pF intro-
duces errors due to the rise time of the switched cur-
rent source.
Nearly all noise sources tested cause additional error
measurements, typically by +1ꢀ° to +10ꢀ°, depending
on the frequency and amplitude (see the Typical
Operating Characteristics).
PC Board Layout
1) Place the MAX1668/MAX1805/MAX1989 as close as
practical to the remote diode. In a noisy environment,
such as a computer motherboard, this distance can
Self-heating does not significantly affect measurement
accuracy. Remote-sensor self-heating due to the diode
current source is negligible. For the local diode, the
8
_______________________________________________________________________________________
Multichannel Remote/Local
Temperature Sensors
be 4in to 8in (typ) or more as long as the worst noise
sources (such as °RTs, clock generators, memory
buses, and ISA/P°I buses) are avoided.
GND
10mils
2) Do not route the DXP_ to DXN_ lines next to the
deflection coils of a °RT. Also, do not route the
traces across a fast memory bus, which can easily
introduce +30ꢀ° error, even with good filtering.
Otherwise, most noise sources are fairly benign.
10mils
10mils
DXP_
MINIMUM
10mils
DXN_
GND
3) Route the DXP_ and DXN_ traces in parallel and in
close proximity to each other, away from any high-
voltage traces such as +12VD°. Leakage currents
from P° board contamination must be dealt with
carefully, since a 20MΩ leakage path from DXP_ to
ground causes about +1ꢀ° error.
Figure 2. Recommended DXP_/DXN_ PC Traces
• Place the noise filter and the 0.1µF V
bypass
°°
capacitors close to the MAX1668/MAX1805/
MAX1989.
4) °onnect guard traces to GND on either side of the
DXP_ to DXN_ traces (Figure 2). With guard traces
in place, routing near high-voltage traces is no
longer an issue.
• Add a 200Ω resistor in series with V
for best noise
°°
filtering (see the Typical Operating Circuit).
Twisted-Pair and Shielded Cables
For remote-sensor distances longer than 8in, or in partic-
ularly noisy environments, a twisted pair is recommend-
ed. Its practical length is 6ft to 12ft (typ) before noise
becomes a problem, as tested in a noisy electronics lab-
oratory. For longer distances, the best solution is a
shielded twisted pair like that used for audio micro-
phones. For example, Belden #8451 works well for dis-
tances up to 100ft in a noisy environment. °onnect the
twisted pair to DXP_ and DXN_ and the shield to GND,
and leave the shield’s remote end unterminated.
5) Route through as few vias and crossunders as possi-
ble to minimize copper/solder thermocouple effects.
6) When introducing a thermocouple, make sure that
both the DXP_ and the DXN_ paths have matching
thermocouples. In general, P° board-induced ther-
mocouples are not a serious problem. A copper-sol-
der thermocouple exhibits 3µV/ꢀ°, and it takes
about 200µV of voltage error at DXP_ to DXN_ to
cause a +1ꢀ° measurement error. So, most para-
sitic thermocouple errors are swamped out.
7) Use wide traces. Narrow ones are more inductive
and tend to pick up radiated noise. The 10mil
widths and spacings recommended in Figure 2 are
not absolutely necessary (as they offer only a minor
improvement in leakage and noise), but try to use
them where practical.
Excess capacitance at DX_ _ limits practical remote-sen-
sor distances (see the Typical Operating Characteristics).
For very long cable runs, the cable’s parasitic capaci-
tance often provides noise filtering, so the 2200pF capac-
itor can often be removed or reduced in value.
°able resistance also affects remote-sensor accuracy;
1Ω series resistance introduces about +0.5ꢀ° error.
8) °opper cannot be used as an EMI shield, and only
ferrous materials such as steel work well. Placing a
copper ground plane between the DXP_ to DXN_
traces and traces carrying high-frequency noise sig-
nals does not help reduce EMI.
Low-Power Standby Mode
Standby mode disables the AD° and reduces the sup-
ply-current drain to less than 12µA. Enter standby
mode by forcing the STBY pin low or through the
RUN/STOP bit in the configuration byte register.
Hardware and software standby modes behave almost
identically: all data is retained in memory, and the SMB
interface is alive and listening for reads and writes.
PC Board Layout Checklist
• Place the MAX1668/MAX1805/MAX1989 as close as
possible to the remote diodes.
• Keep traces away from high voltages (+12V bus).
• Keep traces away from fast data buses and °RTs.
• Use recommended trace widths and spacings.
• Place a ground plane under the traces.
Activate hardware standby mode by forcing the STBY
pin low. In a notebook computer, this line can be con-
nected to the system SUSTAT# suspend-state signal.
The STBY pin low state overrides any software conversion
command. If a hardware or software standby command
is received while a conversion is in progress, the conver-
• Use guard traces flanking DXP_ and DXN_ and con-
necting to GND.
_______________________________________________________________________________________
9
Multichannel Remote/Local
Temperature Sensors
sion cycle is truncated, and the data from that conversion
is not latched into either temperature-reading register. The
previous data is not changed and remains available.
tion. Use caution with the shorter protocols in multimaster
systems, since a second master could overwrite the com-
mand byte without informing the first master.
In standby mode, supply current drops to about 3µA.
At very low supply voltages (under the power-on-reset
threshold), the supply current is higher due to the
address pin bias currents. It can be as high as 100µA,
depending on ADD0 and ADD1 settings.
The temperature data format is 7 bits plus sign in two’s-com-
plement form for each channel, with each data bit represent-
ing 1ꢀ° (Table 2), transmitted MSB first. Measurements are
offset by +0.5ꢀ° to minimize internal rounding errors; for
example, +99.6ꢀ° is reported as +100ꢀ°.
SMBus Digital Interface
From a software perspective, the MAX1668/MAX1805/
MAX1989 appear as a set of byte-wide registers that
contain temperature data, alarm threshold values, or
control bits. A standard SMBus 2-wire serial interface is
used to read temperature data and write control bits and
alarm threshold data. Each A/D channel within the
devices responds to the same SMBus slave address for
normal reads and writes.
Alarm Threshold Registers
Ten (six for MAX1805) registers store alarm threshold
data, with high-temperature (T
) and low-tempera-
HIGH
ture (T
) registers for each A/D channel. If either
LOW
measured temperature equals or exceeds the corre-
sponding alarm threshold value, an ALERT interrupt is
asserted.
The power-on-reset (POR) state of all T
registers of
HIGH
the MAX1668 and MAX1805 is full scale (0111 1111, or
+127ꢀ°). The POR state of the channel 1 T register
The MAX1668/MAX1805/MAX1989 employ four standard
SMBus protocols: write byte, read byte, send byte, and
receive byte (Figure 3). The shorter receive byte protocol
allows quicker transfers, provided that the correct data
register was previously selected by a read byte instruc-
HIGH
of the MAX1989 is 0110 1110 or +110ꢀ°, while all other
channels are at +127ꢀ°. The POR state of all T
isters is 1100 1001 or -55ꢀ°.
reg-
LOW
Write Byte Format
S
ADDRESS
WR
ACK
COMMAND
ACK
DATA
ACK
P
7 bits
8 bits
8 bits
1
Slave Address: equiva-
lent to chip-select line of
a 3-wire interface
°ommand Byte: selects which
register you are writing to
Data Byte: data goes into the register
set by the command byte (to set
thresholds, configuration masks, and
sampling rate)
Read Byte Format
S
ADDRESS
WR
ACK
COMMAND
ACK
S
ADDRESS
RD
ACK
DATA
///
P
7 bits
8 bits
7 bits
8 bits
Slave Address: equiva-
lent to chip-select line
°ommand Byte: selects
which register you are
reading from
Slave Address: repeated
due to change in data-
flow direction
Data Byte: reads from
the register set by the
command byte
Send Byte Format
Receive Byte Format
S
ADDRESS WR ACK COMMAND ACK
P
S
ADDRESS
RD
ACK DATA
8 bits
///
P
7 bits
8 bits
7 bits
Data Byte: This command only
works immediately following a
Read Byte. Reads data from the
register commanded by that last
Read Byte; also used for SMBus
Alert Response return address
°ommand Byte: sends com-
mand with no data
S = Start condition
P = Stop condition
Shaded = Slave transmission
/// = Not acknowledged
Figure 3. SMBus Protocols
10 ______________________________________________________________________________________
Multichannel Remote/Local
Temperature Sensors
Table 2. Data Format (Two’s Complement)
Table 3. Read Format for Alert Response
Address (0001100)
ROUNDED
TEMP
TEMP
(ꢀC)
DIGITAL OUTPUT DATA BITS
BIT
NAME
FUNCTION
(ꢀC)
SIGN
0
MSB
111
111
111
111
001
000
000
000
000
000
111
111
110
110
100
100
011
011
LSB
1111
1111
1111
1110
1001
0000
0000
0000
0000
0000
1111
1111
0111
0110
1001
1001
1111
1111
7
ADD7
+130.00
+127.00
+126.50
+126.00
+25.25
+0.50
+127
+127
+127
+126
+25
+1
(MSB)
0
6
5
4
3
2
1
ADD6
ADD5
ADD4
ADD3
ADD2
ADD1
Provide the current
0
MAX1668/MAX1805/MAX1989
slave address that was latched at
POR (Table 8)
0
0
0
+0.25
+0
0
+0.00
+0
0
0
1
Logic 1
-0.25
+0
0
(LSB)
-0.50
+0
0
-0.75
-1
1
-1.00
-1
1
Interrupts are generated in response to T
and T
LOW
HIGH
-25.00
-25.50
-54.75
-55.00
-65.00
-70.00
-25
-25
-55
-55
-65
-65
1
comparisons and when a remote diode is disconnected
(for continuity fault detection). The interrupt does not halt
automatic conversions; new temperature data continues
to be available over the SMBus interface after ALERT is
asserted. The interrupt output pin is open drain so that
devices can share a common interrupt line. The interrupt
rate can never exceed the conversion rate.
1
1
1
1
1
The interface responds to the SMBus alert response
address, an interrupt pointer return-address feature
(see Alert Response Address section). Prior to taking
corrective action, always check to ensure that an inter-
rupt is valid by reading the current temperature.
Diode Fault Alarm
There is a continuity fault detector at DXP_ that detects
whether the remote diode has an open-circuit condi-
tion. At the beginning of each conversion, the diode
fault is checked, and the status byte is updated. This
fault detector is a simple voltage detector; if DXP_ rises
Alert Response Address
The SMBus alert response interrupt pointer provides
quick fault identification for simple slave devices that
lack the complex, expensive logic needed to be a bus
master. Upon receiving an ALERT interrupt signal, the
host master can broadcast a receive byte transmission
to the alert response slave address (0001 100). Then
any slave device that generated an interrupt attempts
to identify itself by putting its own address on the bus
(Table 3).
above V
- 1V (typ) due to the diode current source, a
°°
fault is detected. Note that the diode fault is not
checked until a conversion is initiated, so immediately
after power-on reset, the status byte indicates no fault
is present, even if the diode path is broken.
If any remote channel is shorted (DXP_ to DXN_ or
DXP_ to GND), the AD° reads 0000 0000 so as not to
trip either the T
or T
alarms at their POR set-
LOW
HIGH
tings. In applications that are never subjected to 0ꢀ° in
normal operation, a 0000 0000 result can be checked
to indicate a fault condition in which DXP_ is acciden-
tally short circuited. Similarly, if DXP_ is short circuited
The alert response can activate several different slave
devices simultaneously, similar to the I2° general call. If
more than one slave attempts to respond, bus arbitra-
tion rules apply, and the device with the lower address
code wins. The losing device does not generate an
acknowledge and continues to hold the ALERT line low
until serviced (implies that the host interrupt input is
to V , the AD° reads +127ꢀ° for all remote and local
°°
channels, and the device alarms.
ALERT
Interrupts
The ALERT interrupt output signal is latched and can
only be cleared by reading the alert response address.
______________________________________________________________________________________ 11
Multichannel Remote/Local
Temperature Sensors
level sensitive). Successful reading of the alert
response address clears the interrupt latch.
state is 0000 0000, so that a receive byte transmission
(a protocol that lacks the command byte) that occurs
immediately after POR returns the current local temper-
ature data.
Command Byte Functions
The 8-bit command byte register (Table 4) is the master
index that points to the various other registers within the
MAX1668/MAX1805/MAX1989. The register’s POR
Table 4. Command Byte Bit Assignments for MAX1668/MAX1805/MAX1989
REGISTER
RIT
COMMAND
00h
POR STATE
0000 0000*
0000 0000*
0000 0000*
0000 0000*
0000 0000*
0000 0000
0000 0000
0000 0000
0111 1111
1100 1001
FUNCTION
Read local temperature
RET1
RET2
RET3**
RET4**
RS1
01h
Read remote DX1 temperature
Read remote DX2 temperature
Read remote DX3 temperature
Read remote DX4 temperature
Read status byte 1
02h
03h
04h
05h
RS2
06h
Read status byte 2
RC
07h
Read Configuration Byte
RIHL
08h
Read local T
Read local T
limit
limit
HIGH
LOW
RILL
09h
0111 1111
(0110 1110)
REHL1
0Ah
Read remote DX1 T
limit (MAX1989)
HIGH
RELL1
REHL2
RELL2
0Bh
0Ch
0Dh
0Eh
0Fh
10h
11h
12h
13h
14h
15h
16h
17h
18h
19h
1Ah
1Bh
1Ch
FEh
1100 1001
0111 1111
1100 1001
0111 1111
1100 1001
0111 1111
1100 1001
N/A
Read remote DX1 T
Read remote DX2 T
Read remote DX2 T
Read remote DX3 T
Read remote DX3 T
Read remote DX4 T
Read remote DX4 T
limit
limit
limit
limit
limit
limit
limit
LOW
HIGH
LOW
HIGH
LOW
HIGH
LOW
REHL3**
RELL3**
REHL4**
RELL4**
WC
Write configuration byte
WIHL
N/A
Write local T
Write local T
limit
limit
HIGH
LOW
WILL
N/A
WEHI1
WELL1
WEHI2
WELL2
WEHI3**
WELL3**
WEHI4**
WELL4**
MFG ID
N/A
Write remote DX1 T
Write remote DX1 T
Write remote DX2 T
Write remote DX2 T
Write remote DX3 T
Write remote DX3 T
Write remote DX4 T
Write remote DX4 T
limit
limit
limit
limit
limit
limit
limit
limit
HIGH
LOW
HIGH
LOW
HIGH
LOW
HIGH
LOW
N/A
N/A
N/A
N/A
N/A
N/A
N/A
0100 1101
Read manufacture ID
0000 0011 (0000 0101)
[0000 1011]
DEV ID
FFh
Read device ID (for MAX1805) [for MAX1989]
*If the device is in hardware standby mode at POR, all temperature registers read 0°C.
**Not available for MAX1805.
12 ______________________________________________________________________________________
Multichannel Remote/Local
Temperature Sensors
on the status bits to indicate reversals in long-term tem-
perature changes and instead use a current tempera-
ture reading to establish the trend direction.
Manufacturer and Device
ID Codes
Two ROM registers provide manufacturer and device
ID codes. Reading the manufacturer ID returns 4Dh,
which is the ASCII code M (for Maxim). Reading the
device ID returns 03h for MAX1668, 05h for MAX1805,
and 0Bh for MAX1989. If the read word 16-bit SMBus
protocol is employed (rather than the 8-bit Read Byte),
the least significant byte contains the data and the most
significant byte contains 00h in both cases.
Conversion Rate
The MAX1668/MAX1805/MAX1989 are continuously
measuring temperature on each channel. The typical
conversion rate is approximately three conversions/s
(for both devices). The resulting data is stored in the
temperature data registers.
Slave Addresses
The MAX1668/MAX1805/MAX1989 appear to the
SMBus as one device having a common address for all
ADC channels. The device address can be set to one
of nine different values by pin-strapping ADD0 and
ADD1 so that more than one MAX1668/MAX1805/
MAX1989 can reside on the same bus without address
conflicts (Table 8).
Configuration Byte Functions
The configuration byte register (Table 5) is used to
mask (disable) interrupts and to put the device in soft-
ware standby mode.
Status Byte Functions
The two status byte registers (Tables 6 and 7) indicate
which (if any) temperature thresholds have been
exceeded. The first byte also indicates whether the
ADC is converting and whether there is an open circuit
in a remote-diode DXP_ to DXN_ path. After POR, the
normal state of all the flag bits is zero, assuming none
of the alarm conditions are present. The status byte is
cleared by any successful read of the status byte,
unless the fault persists. Note that the ALERT interrupt
latch is not automatically cleared when the status flag
bit is cleared.
The address pin states are checked at POR only, and
the address data stays latched to reduce quiescent
supply current due to the bias current needed for high-Z
state detection.
The MAX1668/MAX1805/MAX1989 also respond to the
SMBus alert response slave address (see the Alert
Response Address section).
POR and Undervoltage Lockout
The MAX1668/MAX1805/MAX1989 have a volatile
memory. To prevent ambiguous power-supply condi-
tions from corrupting the data in memory and causing
When reading the status byte, you must check for inter-
nal bus collisions caused by asynchronous ADC timing,
or else disable the ADC prior to reading the status byte
(through the RUN/STOP bit in the configuration byte).
erratic behavior, a POR voltage detector monitors V
CC
and clears the memory if V
falls below 1.8V (typ, see
CC
the Electrical Characteristics table). When power is first
applied and V rises above 1.85V (typ), the logic
To check for internal bus collisions, read the status
byte. If the least significant 7 bits are ones, discard the
data and read the status byte again. The status bits
LHIGH, LLOW, RHIGH, and RLOW are refreshed on the
SMBus clock edge immediately following the stop con-
dition, so there is no danger of losing temperature-relat-
ed status data as a result of an internal bus collision.
The OPEN status bit (diode continuity fault) is only
refreshed at the beginning of a conversion, so OPEN
data is lost. The ALERT interrupt latch is independent of
the status byte register, so no false alerts are generated
by an internal bus collision.
CC
blocks begin operating, although reads and writes at
V
V
levels below 3V are not recommended. A second
comparator, the ADC UVLO comparator, prevents
CC
CC
the ADC from converting until there is sufficient head-
room (V = 2.8V typ).
CC
Power-Up Defaults
• Interrupt latch is cleared.
• Address select pins are sampled.
• ADC begins converting.
If the THIGH and TLOW limits are close together, it’s
possible for both high-temp and low-temp status bits to
be set, depending on the amount of time between sta-
tus read operations (especially when converting at the
fastest rate). In these circumstances, it’s best not to rely
• Command byte is set to 00h to facilitate quick
remote receive byte queries.
• T
and T
registers are set to max and min
LOW
HIGH
limits, respectively.
______________________________________________________________________________________ 13
Multichannel Remote/Local
Temperature Sensors
Table 5. Configuration Byte Bit Assignments
BIT
NAME
POR
FUNCTION
Masks all ALERT interrupts when high.
7 (MSB)
MASKALL
0
Standby mode control bit. If high, the device immediately stops converting and
enters standby mode. If low, the device converts.
6
RUN/STOP
0
5
4
3
2
0
1
MASK4*
MASK3*
MASK2
MASK1
IBIAS1
0
0
0
0
0
0
Masks remote DX4 interrupts when high.
Masks remote DX3 interrupts when high.
Masks remote DX2 interrupts when high.
Masks remote DX1 interrupts when high.
Medium/low-bias control bit. High = low bias, low = medium bias. IBIAS0 must be low.
High-bias control bit. High bias on DXP_ when high. Overrides IBIAS1.
IBIAS0
*Not available for MAX1805.
Table 6. Status Byte Bit 1 Assignments
BIT
NAME
FUNCTION
A high indicates that the ADC is busy converting.
7 (MSB)
BUSY
†
6
5
4
3
2
1
0
LHIGH
A high indicates that the local high-temperature alarm has activated.
†
LLOW
A high indicates that the local low-temperature alarm has activated.
†
OPEN
ALARM
N/A
A high indicates one of the remote-diode continuity (open-circuit) faults.
†
A high indicates one of the remote-diode channels has over/undertemperature alarm.
N/A
N/A
N/A
N/A
N/A
†
These flags stay high until cleared by POR, or until the status byte register is read.
Table 7. Status Byte 2 Bit Assignments
BIT
NAME
RLOW1
RHIGH1
RLOW2
RHIGH2
RLOW3*
RHIGH3*
RLOW4*
RHIGH4*
FUNCTION
7 (MSB)
A high indicates that the DX1 low-temperature alarm has activated.
A high indicates that the DX1 high-temperature alarm has activated.
A high indicates that the DX2 low-temperature alarm has activated.
A high indicates that the DX2 high-temperature alarm has activated.
A high indicates that the DX3 low-temperature alarm has activated.
A high indicates that the DX3 high-temperature alarm has activated.
A high indicates that the DX4 low-temperature alarm has activated.
A high indicates that the DX4 high-temperature alarm has activated.
6
5
4
3
2
1
0
Note: All flags in this byte stay high until cleared by POR or until the status byte is read.
*Not available for MAX1805.
14 ______________________________________________________________________________________
Multichannel Remote/Local
Temperature Sensors
A
B
C
D
E
F
G
H
I
J
K
t
t
HIGH
LOW
SMBCLK
SMBDATA
t
t
t
t
t
BUF
SU:STA HD:STA
SU:DAT
SU:STO
A = START CONDITION
E = SLAVE PULLS SMBDATA LINE LOW
I = ACKNOWLEDGE CLOCK PULSE
J = STOP CONDITION
K = NEW START CONDITION
B = MSB OF ADDRESS CLOCKED INTO SLAVE
C = LSB OF ADDRESS CLOCKED INTO SLAVE
D = R/W BIT CLOCKED INTO SLAVE
F = ACKNOWLEDGE BIT CLOCKED INTO MASTER
G = MSB OF DATA CLOCKED INTO MASTER
H = LSB OF DATA CLOCKED INTO MASTER
Figure 4. SMBus Read Timing Diagram
A
B
C
D
E
F
G
H
I
J
K
L
M
t
t
HIGH
LOW
SMBCLK
SMBDATA
t
t
t
t
HD:DAT
HD:STA
SU:STA
SU:DAT
t
t
SU:STO
BUF
A = START CONDITION
F = ACKNOWLEDGE BIT CLOCKED INTO MASTER
G = MSB OF DATA CLOCKED INTO SLAVE
H = LSB OF DATA CLOCKED INTO SLAVE
I = SLAVE PULLS SMBDATA LINE LOW
J = ACKNOWLEDGE CLOCKED INTO MASTER
K = ACKNOWLEDGE CLOCK PULSE
L = STOP CONDITION, DATA EXECUTED BY SLAVE
M = NEW START CONDITION
B = MSB OF ADDRESS CLOCKED INTO SLAVE
C = LSB OF ADDRESS CLOCKED INTO SLAVE
D = R/W BIT CLOCKED INTO SLAVE
E = SLAVE PULLS SMBDATA LINE LOW
Figure 5. SMBus Write Timing Diagram
Table 8. Slave Address Decoding (ADD0
and ADD1)
ADD0
ADD1
ADDRESS
0011 000
0011 001
0011 010
0101 001
0101 010
0101 011
1001 100
1001 101
1001 110
GND
GND
GND
High-Z
GND
V
CC
High-Z
High-Z
High-Z
GND
High-Z
V
CC
V
CC
V
CC
V
CC
GND
High-Z
V
CC
Note: High-Z means that the pin is left unconnected and floating.
______________________________________________________________________________________ 15
Multichannel Remote/Local
Temperature Sensors
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information
go to www.maxim-ic.com/packages.)
16 ______________________________________________________________________________________
Multichannel Remote/Local
Temperature Sensors
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information
go to www.maxim-ic.com/packages.)
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 17
© 2003 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
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