LT8709 - Negative Input Synchronous Multi-Topology DC/DC Controller


  • Wide Negative Input Range: –4.5V to –80V
  • Rail-to-Rail Output Current Monitor and Control
  • Input Voltage Regulation for High Impedance Inputs
  • Power Good Indication Pin
  • MODE Pin for Forced CCM (Continuous Conduction Mode) or Pulse-Skipping/DCM (Discontinuous Conduction Mode) Operation
  • Switching Frequency Up to 750kHz
  • Easily Configurable as a Buck, Boost, Buck-Boost, or
  • Inverting Converter with a Single Feedback Pin
  • Can be Synchronized to an External Clock
  • High Gain EN/FBIN Pin Accepts Slowly Varying Input Signals
  • 20-Lead TSSOP Package

Typical Application

LT8709 Typical Application
LT8709 Typical Application


The LT®8709 is a synchronous PWM controller for negativeto- negative or negative-to-positive DC/DC conversion, with rail-to-rail output current monitor and control. The LT8709 is ideal for many local power supply designs. It can be easily configured in buck, boost, buck-boost, and inverting topologies with negative input voltages.

In addition, the LT8709’s rail-to-rail output current sense allows the part to be configured in current limited applications such as battery or capacitor charging. The PG pin is used for power good indication.

The LT8709’s switching frequency range can be set between 100kHz and 750kHz. The part may be clocked internally at a frequency set by the resistor from the RT pin to the –VIN pin, or it may be synchronized to an external clock.

The LT8709 also features innovative EN/FBIN pin circuitry that allows for slowly varying input signals and an adjustable undervoltage lockout function. The pin is also used as input voltage regulation to avoid collapsing a high impedance input supply. Additional features such as frequency foldback, thermal shutdown and soft-start are integrated. The LT8709 is available in a 20-lead TSSOP 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
LT8709EFE#PBF TSSOP-20 FE E 05-08-1663 (CB) Yes
LT8709EFE#TRPBF TSSOP-20 FE E 05-08-1663 (CB) Yes
LT8709IFE#PBF TSSOP-20 FE I 05-08-1663 (CB) Yes
LT8709IFE#TRPBF TSSOP-20 FE I 05-08-1663 (CB) Yes

LT8709 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
LT8709EFE#PBF TSSOP-20 E $5.22 $3.65 Yes
LT8709EFE#TRPBF TSSOP-20 E $3.71 Yes
LT8709IFE#PBF TSSOP-20 I $5.97 $4.18 Yes
LT8709IFE#TRPBF TSSOP-20 I $4.24 Yes
Buy NowRequest Samples
* 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
DC2148A LT8709EFE Demo Board | Negative Buck-Boost, -38V ≤ VIN ≤ -4.5V; VOUT = -12V @ 5A $175.00
Buy Now
Click here to view our complete list of demo boards


  • High Power Negative Input, Negative Output Power Supplies
  • High Power Negative Input, Positive Output Power Supplies
  • Telecom Equipment Power Supplies
  • Cathodic Protection Power Supplies

Product Notifications

Please login to your MyLinear account for notifications of datasheet updates, new document releases and LTspice model announcements for your favorite products. If you do not have a MyLinear account you may Sign Up Now.

Forgot your password? Click here.
Need help? Email with questions and comments.

Design Tools


LTspice® software is a powerful, fast and free simulation tool, schematic capture and waveform viewer with enhancements and models for improving the simulation of switching regulators. Click here to download LTspice

To launch a ready to run LTspice demonstration circuit for this part:

To explore other ready to run LTspice demonstration circuits, please visit our Demo Circuits Collection.

Models for the following parts are available in LTspice:

Technical Support