Multichannel Remote/Local Temperature Sensors

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The MAX1668/MAX1805/MAX1989 are precise multichannel digital thermometers that report the temperature of all remote sensors and their own packages. The remote sensors are diode-connected transistors—typically low-cost, easily mounted 2N3904 NPN types—that replace conventional thermistors or thermocouples. Remote accuracy is ±3°C for multiple transistor manufacturers, with no calibration needed. The remote channels 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 format 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.
MAX1668, MAX1805, MAX1989: Typical Operating Circuit MAX1668, MAX1805, MAX1989: Typical Operating Circuit Enlarge+

Key Features

  • 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
    • ±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 Current
  • 700µA (max) Supply Current
  • Small, 16-Pin QSOP/TSSOP Packages


  • Central Office Telecom Equipment
  • Desktop/Notebook Computers
  • Industrial Controls
  • LAN Servers
  • Multichip Modules
  • Test and Measurement Equipment

See parametric specs for Temperature Sensors (113)

Part NumberSensor TypeAlarm OutputFunctionsInterface#ChannelsAccuracy
Parasite Pwr.Temp. Resolution
Oper. Temp.
(See Notes)
MAX1668 RemoteAlertRemote & Local Sensor2-Wire/I2C/SMBusFour2No8-55 to +125
$4.24 @1k
MAX1805 Two
$3.52 @1k
MAX1989 Four
$4.01 @1k

Pricing Notes:
This pricing is BUDGETARY, for comparing similar parts. Prices are in U.S. dollars and subject to change. Quantity pricing may vary substantially and international prices may differ due to local duties, taxes, fees, and exchange rates. For volume-specific and version-specific prices and delivery, please see the price and availability page or contact an authorized distributor.
Product Reliability Reports: MAX1668.pdf 
Device   Fab Process   Technology   Sample size   Rejects   FIT at 25°C   FIT at 55°C   Material Composition  

Note : The failure rates are summarized by technology and mapped to the associated material part numbers. The failure rates are highly dependent on the number of units tested.

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