LT3669/LT3669-2 - IO-Link Transceiver with Integrated Step-Down Regulator and LDO


  • IO-Link® PHY Compatible (COM1/COM2/COM3)
  • Cable Interface Protected to ±60V
  • Operation from 7.5V to 40V
  • Integrated Step-Down Switching Regulator
  • Max Load Current: 100mA (LT3669)/300mA (LT3669-2)
  • Synchronizable and Adjustable Switching Frequency: 250kHz to 2.2MHz
  • Output Voltage: 0.8V to 16V
  • Integrated 150mA LDO Linear Regulator
  • Rugged Line Drivers with Adjustable Slew Rate and Current Limit
  • Adaptive Line Driver Pulsing Scheme to Switch Heavy Loads Safely
  • Drivers Configurable as Push-Pull, Pull-Up or Pull-Down
  • Adjustable Power-On Reset Timer
  • Small 28-Pin Thermally Enhanced 4mm × 5mm QFN Package

Typical Application

LT3669 Typical Application
LT3669 Typical Application


The LT®3669 is an industrial transceiver that includes a step-down switching regulator and a low dropout linear regulator. Wake-up detect functionality, as well as a programmable power-on reset timer are also included. The current limit and slew rate of the transmitters are externally adjustable for optimum EMC performance.

The line drivers can source/sink up to 250mA of current each or 500mA when connected together, with a minimal residual voltage of less than 2.1V. An internal adaptive pulsing scheme allows the drivers to safely switch heavy capacitive loads and incandescent bulbs. Thermal shutdown provides additional protection. Line protection of ±60V in the line interface pins allows the use of standard TVS diodes with L+ operating voltages up to 40V.

The switching regulator integrates the catch diode in LT3669 (up to 100mA load current) and requires an external catch diode in LT3669-2 (up to 300mA load current).

The LT3669 implements an IO-Link device PHY. For IO-Link master designs, see the LTC2874.


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
LT3669EUFD-2#PBF 4x5 QFN-28 UFD E 05-08-1712 Yes
LT3669EUFD-2#TRPBF 4x5 QFN-28 UFD E 05-08-1712 Yes
LT3669EUFD#PBF 4x5 QFN-28 UFD E 05-08-1712 Yes
LT3669EUFD#TRPBF 4x5 QFN-28 UFD E 05-08-1712 Yes
LT3669HUFD-2#PBF 4x5 QFN-28 UFD H 05-08-1712 Yes
LT3669HUFD-2#TRPBF 4x5 QFN-28 UFD H 05-08-1712 Yes
LT3669HUFD#PBF 4x5 QFN-28 UFD H 05-08-1712 Yes
LT3669HUFD#TRPBF 4x5 QFN-28 UFD H 05-08-1712 Yes
LT3669IUFD-2#PBF 4x5 QFN-28 UFD I 05-08-1712 Yes
LT3669IUFD-2#TRPBF 4x5 QFN-28 UFD I 05-08-1712 Yes
LT3669IUFD#PBF 4x5 QFN-28 UFD I 05-08-1712 Yes
LT3669IUFD#TRPBF 4x5 QFN-28 UFD I 05-08-1712 Yes

LT3669 Package Drawing
LT3669 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
LT3669EUFD-2#PBF 4x5 QFN-28 E $5.07 $3.55 Yes
LT3669EUFD-2#TRPBF 4x5 QFN-28 E $3.61 Yes
LT3669EUFD#PBF 4x5 QFN-28 E $5.07 $3.55 Yes
LT3669EUFD#TRPBF 4x5 QFN-28 E $3.61 Yes
LT3669HUFD-2#PBF 4x5 QFN-28 H $6.19 $4.33 Yes
LT3669HUFD-2#TRPBF 4x5 QFN-28 H $4.39 Yes
LT3669HUFD#PBF 4x5 QFN-28 H $6.19 $4.33 Yes
LT3669HUFD#TRPBF 4x5 QFN-28 H $4.39 Yes
LT3669IUFD-2#PBF 4x5 QFN-28 I $5.83 $4.08 Yes
LT3669IUFD-2#TRPBF 4x5 QFN-28 I $4.14 Yes
LT3669IUFD#PBF 4x5 QFN-28 I $5.83 $4.08 Yes
LT3669IUFD#TRPBF 4x5 QFN-28 I $4.14 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.

Part Number Description Price Documentation
DC1733A-A LT3669-1 Demo Board | 7.5V to 40V input with Vout 1 being 5V at 100mA and Vout 2 (LDO) being 3.3V at 100mA $125.00
DC1733A-B LT3669-2 Demo Board | 7.5V to 40V input with Vout 1 being 5V at 300mA and Vout 2 (LDO) being 3.3V at 150mA Contact Factory
DC2227A LT3669-2 Demo Board | I/O Link with 18V to 36V Input to 4V at 300mA and 3.3V at 150mA $299.00
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Companion Boards

Part Number Description Price Documentation
DC2228A 8-Port IO-Link Master Reference Design. Includes LTC2874, LT4275A, IO-Link v1.1 Protocol Stack and Control Tool. Optionally powered by DC1814A-D PoE supply. $599.00
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Click here to view our complete list of demo boards


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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:

  • LTspice - A powerful SPICE simulator, schematic capture and waveform viewer with enhancements and models for easing the simulation of switching regulators
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