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MAX1668MEEMAXN/a33avaiMultichannel Remote/Local Temperature Sensors
MAX1805MEEMAXN/a20avaiMultichannel Remote/Local Temperature Sensors
MAX1989MEEMAXN/a102avaiMultichannel Remote/Local Temperature Sensors
MAX1989MEEMAXIM ?N/a1800avaiMultichannel Remote/Local Temperature Sensors
MAX1989MEEMAXIMN/a6698avaiMultichannel Remote/Local Temperature Sensors
MAX1989MUEMAXIMN/a80avaiMultichannel Remote/Local Temperature Sensors
MAX1989MUEMAXN/a80avaiMultichannel Remote/Local Temperature Sensors


MAX1989MEE ,Multichannel Remote/Local Temperature SensorsELECTRICAL CHARACTERISTICS (continued)(V = +3.3V, STBY = V , configuration byte = X0XXXX00, T = 0°C ..
MAX1989MEE ,Multichannel Remote/Local Temperature SensorsGeneral Description ________
MAX1989MEE ,Multichannel Remote/Local Temperature SensorsFeaturesThe MAX1668/MAX1805/MAX1989 are precise multi- Multichannelchannel digital thermometers th ..
MAX1989MEE+ ,Multichannel Remote/Local Temperature SensorsELECTRICAL CHARACTERISTICS (continued)(V = +3.3V, STBY = V , configuration byte = X0XXXX00, T = 0°C ..
MAX1989MEE+ ,Multichannel Remote/Local Temperature SensorsFeaturesThe MAX1668/MAX1805/MAX1989 are precise multi-♦ Multichannelchannel digital thermometers th ..
MAX1989MEE+T ,Multichannel Remote/Local Temperature SensorsELECTRICAL CHARACTERISTICS(V = +3.3V, STBY = V , configuration byte = X0XXXX00, T = 0°C to +125°C, ..
MAX5020CSA ,Current-mode PWM controller with integrated startup circuitFeaturesThe MAX5019/MAX5020 integrate all the building Wide Input Range: (18V to 110V) or (13V to ..
MAX5020CSA+ ,Current-Mode PWM Controllers with Integrated Startup CircuitFeaturesThe MAX5019/MAX5020 integrate all the building♦ Wide Input Range: (18V to 110V) or (13V to ..
MAX5020ESA ,Current-Mode PWM Controllers with Integrated Startup CircuitFeaturesThe MAX5019/MAX5020 integrate all the building♦ Wide Input Range: (18V to 110V) or (13V to ..
MAX5020ESA ,Current-Mode PWM Controllers with Integrated Startup CircuitApplicationsMAX5020ESA* -40°C to +85°C8-SO*See Selector Guide at end of data sheet.Telecom Power Su ..
MAX5020ESA ,Current-Mode PWM Controllers with Integrated Startup CircuitFeaturesThe MAX5019/MAX5020 integrate all the building♦ Wide Input Range: (18V to 110V) or (13V to ..
MAX5020ESA+ ,Current-Mode PWM Controllers with Integrated Startup CircuitMAX5019/MAX502019-2115; Rev 0; 7/01Current-Mode PWM Controllers with IntegratedStartup Circuit


MAX1668MEE-MAX1805MEE-MAX1989MEE-MAX1989MUE
Multichannel Remote/Local Temperature Sensors
________________General Description
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 ±3°C for multiple transistor manu-
facturers, with no calibration needed. The remote chan-
nels can also measure the die temperature of other ICs,
such as microprocessors, that contain an on-chip,
diode-connected transistor.
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
1°C, in two’s-complement format.
The MAX1668/MAX1805/MAX1989 are available in
small, 16-pin QSOP surface-mount packages. The
MAX1989 is also available in a 16-pin TSSOP.
________________________Applications
____________________________Features
Multichannel
4 Remote, 1 Local (MAX1668/MAX1989)
2 Remote, 1 Local (MAX1805)
No Calibration RequiredSMBus 2-Wire Serial InterfaceProgrammable Under/Overtemperature AlarmsSupports SMBus Alert ResponseAccuracy
±2°C (+60°C to +100°C, Local)
±3°C (-40°C to +125°C, Local)
±3°C (+60°C to +100°C, Remote)
3µA (typ) Standby Supply Current700µA (max) Supply CurrentSmall, 16-Pin QSOP/TSSOP Packages
MAX1668/MAX1805/MAX1989
Multichannel Remote/Localemperature Sensors

19-1766; Rev 2; 5/03
SMBus is a trademark of Intel Corp.†Patents Pending
Desktop and Notebook
Computers
LAN Servers
Industrial Controls
Central-Office Telecom
Equipment
Test and Measurement
Multichip Modules
MAX1668/MAX1805/MAX1989
Multichannel Remote/Local emperature Sensors
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS

(VCC= +3.3V, STBY= VCC, configuration byte = X0XXXX00, TA= 0°C to +125°C, unless otherwise noted.)
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.
VCCto GND..............................................................-0.3V to +6V
DXP_, ADD_, STBY to GND........................-0.3V to (VCC+ 0.3V)
DXN_ to GND........................................................-0.3V to +0.8V
SMBCLK, SMBDATA, ALERTto GND......................-0.3V to +6V
SMBDATA, ALERTCurrent.................................-1mA to +50mA
DXN_ Current......................................................................±1mA
Continuous Power Dissipation (TA= +70°C)
QSOP (derate 8.30mW/°C above +70°C)....................667mW
TSSOP (derate 9.40mW/°C above +70°C)..................755mW
Operating Temperature Range.........................-55°C to +125°C
Junction Temperature......................................................+150°C
Storage Temperature Range.............................-65°C to +150°C
Lead Temperature (soldering, 10s).................................+300°C
MAX1668/MAX1805/MAX1989
Multichannel Remote/Local emperature Sensors
ELECTRICAL CHARACTERISTICS (continued)

(VCC= +3.3V, STBY= VCC, configuration byte = X0XXXX00, TA= 0°C to +125°C, unless otherwise noted.)
ELECTRICAL CHARACTERISTICS

(VCC= +5V, STBY= VCC, configuration byte = X0XXXX00, TA= -55°C to +125°C, unless otherwise noted.) (Note 6)
ypical Operating Characteristics(Typical Operating Circuit, VCC= +5V, STBY= VCC, configuration byte = X0XXXX00, TA = +25°C, unless otherwise noted.)
MAX1668/MAX1805/MAX1989
Multichannel Remote/Local emperature Sensors
ELECTRICAL CHARACTERISTICS (continued)

(VCC= +5V, STBY= VCC, configuration byte = X0XXXX00, TA= -55°C to +125°C, unless otherwise noted.) (Note 6)
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 +66.7°C, the ADC may report +66°C, +67°C, or +68°C (due to the quantization
error plus the +0.5°C offset used for rounding up) and still be within the guaranteed ±1°C error limits for the +60°C to
+100°C temperature range. See Table 2.
Note 3:
A remote diode is any diode-connected transistor from Table 1. TRis the junction temperature of the remote diode. See the
Remote-Diode Selectionsection for remote-diode forward-voltage requirements.
Note 4:
The SMBus logic block is a static design that works with clock frequencies down to DC. 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
SMBCLK’s falling edge tHD:DAT.
Note 6:
Specifications from -55°C to +125°C are guaranteed by design, not production tested.
MAX1668/MAX1805/MAX1989
Multichannel Remote/Local emperature Sensors

TEMPERATURE ERROR
vs. COMMON-MODE NOISE FREQUENCY

MAX1668/1805 toc04
FREQUENCY (MHz)
TEMPERATURE ERROR (100
2.0ypical Operating Characteristics (continued)
(Typical Operating Circuit, VCC= +5V, STBY= VCC, configuration byte = X0XXXX00, TA = +25°C, unless otherwise noted.)
MAX1668/MAX1805/MAX1989
Multichannel Remote/Local emperature Sensors
_______________Detailed Description

The MAX1668/MAX1805/MAX1989 are temperature
sensors designed to work in conjunction with an exter-
nal microcontroller (µC) or other intelligence in thermo-
static, process-control, or monitoring applications. The
µC 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.
These devices are essentially 8-bit serial analog-to-digi-
tal converters (ADCs) with sophisticated front ends.
However, the MAX1668/MAX1805/MAX1989 also contain
a switched current source, a multiplexer, an ADC, an
SMBus interface, and associated control logic (Figure 1).
In the MAX1668 and MAX1989, temperature data from
the ADC 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 ADC is loaded into
three data registers, where it is automatically compared
with data previously stored in six over/undertemperature
alarm registers.
ADC and Multiplexer

The ADC is an averaging type that integrates over a
64ms period (each channel, typical), with excellent
noise rejection.
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.
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 +0.5°C error per ohm. Likewise, 200µV of offset
voltage forced on DXP_ to DXN_causes about 1°C error.
MAX1668/MAX1805/MAX1989
Multichannel Remote/Local emperature Sensors

Figure 1. MAX1668/MAX1805/MAX1989 Functional Diagram
A/D Conversion Sequence
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 ADC is
busy, the results of the previous conversion are always
available.
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 CPUs and
other ICs having on-board temperature-sensing diodes.
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.
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 +1°C after a
sudden +100°C 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.
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
worst-case error occurs when sinking maximum current
at the ALERToutput. For example, with ALERTsinking
1mA, the typical power dissipation is VCCx 400µA plus
0.4V x 1mA. Package theta J-A is about 150°C/W, so
with VCC= 5V and no copper PC board heat sinking,
the resulting temperature rise is:
dT = 2.4mW x 150°C/W = 0.36°C
Even with these contrived circumstances, it is difficult
to introduce significant self-heating errors.
ADC Noise Filtering

The ADC 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 PC board layout and proper
external noise filtering are required for high-accuracy
remote measurements in electrically noisy environments.
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 +1°C to +10°C, depending
on the frequency and amplitude (see the Typical
Operating Characteristics).
PC Board Layout
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
MAX1668/MAX1805/MAX1989
Multichannel Remote/Local emperature Sensors
Table 1. Remote-Sensor Transistor
Manufacturers
Note:
Transistors must be diode connected (base shorted to
collector).
be 4in to 8in (typ) or more as long as the worst noise
sources (such as CRTs, clock generators, memory
buses, and ISA/PCI buses) are avoided.Do not route the DXP_ to DXN_ lines next to the
deflection coils of a CRT. Also, do not route the
traces across a fast memory bus, which can easily
introduce +30°C error, even with good filtering.
Otherwise, most noise sources are fairly benign.Route the DXP_ and DXN_ traces in parallel and in
close proximity to each other, away from any high-
voltage traces such as +12VDC. Leakage currents
from PC board contamination must be dealt with
carefully, since a 20MΩleakage path from DXP_ to
ground causes about +1°C error.Connect 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. Route through as few vias and crossunders as possi-
ble to minimize copper/solder thermocouple effects. When introducing a thermocouple, make sure that
both the DXP_ and the DXN_ paths have matching
thermocouples. In general, PC board-induced ther-
mocouples are not a serious problem. A copper-sol-
der thermocouple exhibits 3µV/°C, and it takes
about 200µV of voltage error at DXP_ to DXN_ to
cause a +1°C measurement error. So, most para-
sitic thermocouple errors are swamped out. 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.Copper 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.
PC Board Layout Checklist
Place the MAX1668/MAX1805/MAX1989as close as
possible to the remote diodes.Keep traces away from high voltages (+12V bus).Keep traces away from fast data buses and CRTs.Use recommended trace widths and spacings.Place a ground plane under the traces.Use guard traces flanking DXP_ and DXN_ and con-
necting to GND.Place the noise filter and the 0.1µF VCCbypass
capacitors close to the MAX1668/MAX1805/
MAX1989.Add a 200Ωresistor in series with VCCfor 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. Connect the
twisted pair to DXP_ and DXN_ and the shield to GND,
and leave the shield’s remote end unterminated.
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.
Cable resistance also affects remote-sensor accuracy;series resistance introduces about +0.5°C error.
Low-Power Standby Mode

Standby mode disables the ADC and reduces the sup-
ply-current drain to less than 12µA. Enter standby
mode by forcing the STBYpin 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.
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 STBYpin low state overrides any software conversion
command. If a hardware or software standby command
is received while a conversion is in progress, the conver-
MAX1668/MAX1805/MAX1989
Multichannel Remote/Local emperature Sensors

Figure 2. Recommended DXP_/DXN_ PC Traces
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