Synchronous SEPIC/Inverting/Boost Controller with Output Current Control
Features and Benefits
- 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
The LT8709 is a synchronous PWM controller for negative-to-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.
- 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 Lifecycle Production
At least one model within this product family is in production and available for purchase. The product is appropriate for new designs but newer alternatives may exist.
Evaluation Kits (1)
Demonstration circuit 2148A features the LT8709, a negative input synchronous multi-topology DC/DC controller designed for negative input power supplies where the highest input supply voltage is ground. Examples of these circuits include negative buck, negative boost, negative buck-boost and negative inverting. The DC2148A is a negative buck-boost with an operating input voltage range from –4.5V to –38V and an output voltage of –12V, however this demo circuit can be easily reconfigured for other negative input topologies. The maximum output current for DC2148A is 5A, the switching frequency is 400kHz and the maximum efficiency with a –12V input is 91%.
Tools & Simulations
LTspice® is a powerful, fast and free simulation software, schematic capture and waveform viewer with enhancements and models for improving the simulation of analog circuits.
To launch ready-to-run LTspice demonstration circuits for this part:
Step 1: Download and install LTspice on your computer.
Step 2: Click on the link in the section below to download a demonstration circuit.
Step 3: If LTspice does not automatically open after clicking the link below, you can instead run the simulation by right clicking on the link and selecting “Save Target As.” After saving the file to your computer, start LTspice and open the demonstration circuit by selecting ‘Open’ from the ‘File’ menu.
Models for the following parts are available in LTspice:
LT8709 Companion Parts
Recommended Related Parts
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Sample & Buy
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 Analog Devices, Inc. sales office or authorized distributor. Pricing displayed for Evaluation Boards and Kits is based on 1-piece pricing.