LTC1840 - Dual Fan Controller with 2-Wire Interface


  • Two 8-Bit Current DACs
  • DACs Guaranteed Monotonic
  • Known IC State on Power-Up
  • Serial Interface Watchdog Timer with Disable
  • 2-Wire Serial Interface Compatible with I2C™ and SMBus
  • 2 Programmable Fan Tachometer Interfaces
  • 4 Programmable General Purpose I/Os
  • Small 16-Pin SSOP Package
  • Single 2.7V to 5.75V Supply Operation
  • Fault Output Signal
  • Status Register
  • Fan Blasting Function
  • Nine Addresses Using Two Programming Lines

Typical Application

LTC1840 Typical Application


The LTC®1840 is a fan controller with two 8-bit current output DACs, two tachometer interfaces, and four general purpose I/O (GPIO) pins. It operates from a single supply with a range of 2.7V to 5.75V. A current output DAC is used to control an external switching regulator, which controls the fan speed. A current output DAC and tachometer allow a controller to form a closed control loop on fan velocity. The GPIO pins can be used as digital inputs or open drain pull-down outputs.

The part features a simple 2-wire I²C and SMBus compatible serial interface that allows communication between many devices. The interface includes a fault status register that reflects the state of the part and which can be polled to find the cause of a fault condition. Other operational characteristics of the part, such as DAC output currents, GPIO modes, and tachometer frequency, are also programmed through the serial interface. Two address pins provide nine possible device addresses.

The BLAST pin is provided to force the DAC output currents to program the maximum regulator output voltages through a single pin and gate the operation of the serial access timer.


CAD Symbols and Footprints: The downloadable Zip file below contains the schematic symbol and PCB footprints.

For complete and up to date package information and drawings, please refer to our packaging page

Part Number Package Code Temp Package
LTC1840CGN#PBF SSOP-16 GN C 05-08-1641 (GN16) Yes
LTC1840CGN#TRPBF SSOP-16 GN C 05-08-1641 (GN16) Yes
LTC1840IGN#PBF SSOP-16 GN I 05-08-1641 (GN16) Yes
LTC1840IGN#TRPBF SSOP-16 GN I 05-08-1641 (GN16) Yes

LTC1840 Package Drawing

Order Info

  • Part numbers ending in PBF are lead free. Solder plated terminal finish (SnPb) versions are non-standard and special terms and conditions and pricing applies if available. Please contact LTC marketing for information.
  • Part numbers containing TR or TRM are shipped in tape and reel or 500 unit mini tape and reel, respectively
  • Please refer to our general ordering information or the product datasheet for more details

Package Variations and Pricing

Part Number Package Temp Price
LTC1840CGN#PBF SSOP-16 C $3.75 $2.75 Yes
LTC1840CGN#TRPBF SSOP-16 C $2.81 Yes
LTC1840IGN#PBF SSOP-16 I $4.25 $3.15 Yes
LTC1840IGN#TRPBF SSOP-16 I $3.21 Yes
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* The USA list pricing shown is for BUDGETARY USE ONLY, shown in United States dollars (FOB USA per unit for the stated volume), and is subject to change. International prices may differ due to local duties, taxes, fees and exchange rates. For volume-specific price or delivery quotes, please contact your local Linear Technology sales office or authorized distributor.

Demo Boards

Linear Technology offers many demo boards free of charge to qualified customers. Contact your local sales office or distributor to inquire about a demo board. Certain demo boards are also available for sale via credit card on this website. Demo boards are for evaluation purposes only. It remains the customer’s responsibility to verify proper and reliable operation in the actual end application.

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Design Tools

Linear Technology provides a variety of custom design simulation tools and device models to allow even novice designers to quickly and easily evaluate circuits using high performance switching regulators, amplifiers, data converters, filters and more. Please visit our Design Tools page to view and download:

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