LT8708
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LT8708

80V Synchronous 4-Switch Buck-Boost DC/DC Controller with Bidirectional Capability

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Info : RECOMMENDED FOR NEW DESIGNS tooltip
Info : RECOMMENDED FOR NEW DESIGNS tooltip
Part Details
Part Models 12
1ku List Price Starting From $7.13
Features
  • Single Inductor Allows VIN Above, Below, or Equal to VOUT
  • Six Independent Forms of Regulation
    • VIN Current (Forward and Reverse)
    • VOUT Current (Forward and Reverse)
    • VIN and VOUT Voltage
  • Forward and Reverse Discontinuous Conduction Mode Supported
  • Supports MODE and DIR Pin Changes While Switching
  • VINCHIP Range 2.8V (Need EXTVCC > 6.4V) to 80V
  • VOUT Range: 1.3V to 80V
  • Synchronous Rectification: Up to 99% Efficiency
  • Available in 40-Lead (5mm × 8mm) QFN with High Voltage Pin Spacing and 64-Lead (10mm × 10mm) eLQFP
  • AEC-Q100 Qualified for Automotive Applications
Additional Details
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The LT8708 is a high performance buck-boost switching regulator controller that operates from an input voltage that can be above, below or equal to the output voltage. Features are included to simplify bidirectional power conversion in battery/capacitor backup systems and other applications that may need regulation of VOUT, VIN, IOUT, and/or IIN. Forward and reverse current can be monitored and limited for the input and output sides of the converter. All four current limits (forward input, reverse input, forward output and reverse output) can be set independently using four resistors on the PCB.

The MODE pin can select between discontinuous conduction mode (DCM), continuous conduction mode (CCM), hybrid conduction mode (HCM) and Burst Mode® operation. In combination with the DIR (direction) pin, the chip can be configured to process power only from VIN to VOUT or only from VOUT to VIN. With a wide 2.8V to 80V input and 1.3V to 80V output range, the LT8708 is compatible with most solar, automotive, telecom and battery-powered systems.

APPLICATIONS

  • High Voltage Buck-Boost Converters
  • Bidirectional Charging System
  • Automotive 48V Systems
Part Models 12
1ku List Price Starting From $7.13

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Documentation

Documentation

Video

Part Model Pin/Package Drawing Documentation CAD Symbols, Footprints, and 3D Models
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Product Lifecycle

PCN

Apr 6, 2021

- 21_0046

Transfer of LQFP and LQFP_EP from AEM to AET

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PRODUCTION

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PRODUCTION

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Filter by Model

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Part Models

Product Lifecycle

PCN

Apr 6, 2021

- 21_0046

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Transfer of LQFP and LQFP_EP from AEM to AET

LT8708ELWE#PBF

PRODUCTION

LT8708HLWE#PBF

PRODUCTION

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PRODUCTION

Software & Part Ecosystem

Software & Part Ecosystem

Evaluation Kit

Evaluation Kits 2

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DC2596A

LT8708 80V VIN and VOUT Synchronous 4-Switch Buck-Boost DC/DC Controller with Flexible Bidirectional Capability

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DC2596A

LT8708 80V VIN and VOUT Synchronous 4-Switch Buck-Boost DC/DC Controller with Flexible Bidirectional Capability

LT8708 80V VIN and VOUT Synchronous 4-Switch Buck-Boost DC/DC Controller with Flexible Bidirectional Capability

Product Detail

Demonstration circuit 2596A is a high performance bidirectional buck-boost converter featuring the LT®8708 that can operate from input voltages above, below or equal to the output voltage. The demo board input range is 36V to 75V. The output voltage is set at 48V and the output current limit at 6A.

The controller has integrated input voltage and output voltage regulators and two sets of input and output current regulators that control current flow in forward or reverse direction. Features are included that simplify bidirectional power conversion in battery/capacitor backup systems and other applications that may need regulation of VIN, VOUT, IIN and/or IOUT.

While the current mode control limits the inductor current both in normal and in reverse direction these current limits have some variation as input/output voltage changes. The forward and reverse input and output current regulators offer four accurate current limits that can be set individually.

The input voltage regulator is often used in applications with high impedance power sources and will reduce the forward current if the input voltage drops below the set point. When operating with reverse current flow the input voltage regulator regulates the voltage at the input side.

The operating mode of the controller is determined through the MODE pin (jumper JP7 Pins 5 to 12) and can be set to discontinuous mode, hybrid discontinuous mode, forced continuous mode and Burst Mode® Operation.

The LT8708 is capable of bidirectional operation when operating in the continuous conduction mode (CCM). DCM, HCM and Burst Mode operation only allow power to flow in one direction. Additional circuitry may be needed depending on the application.

By feeding the LT8708 from a separate low voltage supply the power dissipation can be reduced. The LT8708 will start when >5.5V voltage is applied at the input (VIN pin), and when it is running it will draw current from the EXTVCC pin if the voltage at the pin is > 6.4V.

Typical efficiency with 5A load is above 96.3% across a 36V to 75V input range.

The LT8708 data sheet gives a complete description of the part, operation and application information. The data sheet should be read in conjunction with this quick start guide for DC2596A. The input voltage range of the LT8708 itself is 2.8V (need EXTVCC > 6.4V) to 80V and the output range is 1.3V to 80V.

The LT8708EUHG is assembled in a 40-Lead (5mm × 7mm) plastic QFN package with a thermal pad underneath the chip. Proper board layout is essential for maximum thermal and electrical performance. See the data sheet Circuit Board Layout Checklist section.

reference details image

DC2719A

LT8708/LT8708-1 80V VIN and VOUT Synchronous 4-Switch Buck-Boost DC/DC Controller with Flexible Bidirectional Capability

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DC2719A

LT8708/LT8708-1 80V VIN and VOUT Synchronous 4-Switch Buck-Boost DC/DC Controller with Flexible Bidirectional Capability

LT8708/LT8708-1 80V VIN and VOUT Synchronous 4-Switch Buck-Boost DC/DC Controller with Flexible Bidirectional Capability

Product Detail

Demonstration circuit 2719A is a high performance bidirectional buck-boost converter featuring the LT8708/ LT8708-1 that can operate from input voltages above, below or equal to the output voltage. The demo board input range is 10.5V to 14.5V (25VMAX). The output voltage is set at 14.5V and the output current limit at 40A. The board can operate in both forward and reverse mode.

The controller has integrated input voltage and output voltage regulators and two sets of input and output current regulators that control current flow in forward or reverse direction. Features are included that simplify bidirectional power conversion in battery/capacitor backup systems and other applications that may need regulation of VIN, VOUT, IIN and/or IOUT.

While the current mode control limits the inductor current both in normal and in reverse direction these current limits have some variation as input/output voltage changes. The forward and reverse input and output current regulators offer four accurate current limits that can be set individually.

The input voltage regulator is often used in applications with high impedance power sources and will reduce the forward current if the input voltage drops below the set point. When operating with reverse current flow, the input voltage regulator regulates the voltage at the input side.

The operating mode of the controller is determined through the MODE pin (jumper JP9 Pins 5 to 12) and can be set to discontinuous mode, hybrid discontinuous mode, forced continuous mode and Burst Mode® operation.

The LT8708 is capable of bidirectional operation when operating in the continuous conduction mode (CCM). DCM, HCM and Burst Mode operation only allow power to flow in one direction. Additional circuitry may be needed depending on the application.

Tools & Simulations

Tools & Simulations 1

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.

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