LT3905 - Boost DC/DC Converter with APD Current Monitor


  • 65V, 350mA Internal DMOS Switch
  • Integrated Schottky Diode
  • 2% Accurate APD Current Monitoring Over the 3μA to 3mA Range
  • Single Resistor Programs Maximum APD Current
  • Fast APD Current Limiter with Indicator
  • Programmable Loss-of-Signal Indicator
  • CTRL Pin Adjusts Output Voltage
  • Programmable VIN Undervoltage Lockout
  • High Efficiency Step-Up Converter
  • Selectable 1MHz/2MHz Switching Frequency
  • Internally Compensated
  • Internal Soft-Start
  • 2.7V to 12V VIN Range
  • Low Shutdown Current: <1μA

Typical Application

LT3905 Typical Application
LT3905 Typical Application


The LT®3905 is a fixed frequency current-mode step-up converter designed to bias avalanche photodiodes (APD) in optical receivers. The LT3905 features high side APD current monitoring over four decades of dynamic range with better than 2% relative accuracy over the 3μA to 3mA range.

The maximum APD current is programmed with a single resistor, and a fast current limiter with indicator protects the APD during overload conditions. Adjustable output voltage provides dynamic bias control, and an adjustable loss-of-signal indicator flags low APD current.

Coupled with the integrated DMOS power switch and Schottky rectifier, the LT3905 provides a compact total solution with few external components and low solution cost. Constant switching frequency results in predictable output noise that is easy to filter.

The LT3905 is available in the tiny footprint (3mm × 3mm) 16-Lead QFN Package.


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
LT3905EUD#PBF 3x3 QFN-16 UD E 05-08-1691 Yes
LT3905EUD#TRPBF 3x3 QFN-16 UD E 05-08-1691 Yes
LT3905IUD#PBF 3x3 QFN-16 UD I 05-08-1691 Yes
LT3905IUD#TRPBF 3x3 QFN-16 UD I 05-08-1691 Yes

LT3905 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
LT3905EUD#PBF 3x3 QFN-16 E $3.64 $2.55 Yes
LT3905EUD#TRPBF 3x3 QFN-16 E $2.61 Yes
LT3905IUD#PBF 3x3 QFN-16 I $4.02 $2.81 Yes
LT3905IUD#TRPBF 3x3 QFN-16 I $2.87 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
DC1956A LT3905 Demo Board | Boost with APD Current Monitor, 2.7V ≤ VIN ≤ 12V, Vout = 50V @ 2mA $125.00
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Click here to view our complete list of demo boards


  • APD Bias
  • PIN Diode Bias
  • Optical Receivers and Modules
  • Fiber Optic Network Equipment

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Design Tools


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