40VIN, 18VOUT, 6A Synchronous Buck-Boost Silent Switcher

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Part Details
Part Models 1
1ku List Price Starting From $3.42
  • 4-Switch Single Inductor Architecture Allows VIN Above, Below or Equal to VOUT
  • Silent Switcher® Architecture for Low EMI
  • Up to 95% Efficiency at 2MHz
  • Proprietary Peak Current Mode
  • 3V to 40V Input Voltage Range
  • 1V to 18V Output Voltage Range
  • ±1.5% Output Voltage Regulation
  • Output/Input Current Regulation and Monitor
  • Constant-Voltage/Constant-Current Regulation
  • High Side PMOS Load Switch Driver
  • No Top MOSFET Refresh Noise in Buck or Boost
  • 200kHz to 2MHz Fixed Switching Frequency with External Frequency Synchronization and SSFM
  • VOUT Disconnected from VIN During Shutdown
  • Small 4mm × 6mm 32-Pin LQFN Package
  • AEC-Q100 Qualification in Progress
Additional Details
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The LT8350 is a monolithic 4-switch synchronous buck-boost converter with Silent Switcher architecture to minimize EMI emissions while delivering high efficiency at high switching frequency. The switcher can regulate the output voltage, input or output current from input voltages above, below, or equal to the output voltage. The proprietary peak current mode control scheme allows adjustable and synchronizable 200kHz to 2MHz fixed frequency operation, or spread spectrum frequency modulation (SSFM) operation. With 3V to 40V input voltage range, 1V to 18V output voltage capability, and seamless low noise transitions between operation regions, the LT8350 is ideal for voltage regulator, battery and supercapacitor charger applications in automotive, industrial, telecom, and battery powered systems.

The LT8350 provides input or output current monitor and power good flag. Robust fault protection is provided to detect output short-circuit condition, during which the LT8350 retries, latches off, or keeps running.


  • Automotive, Industrial, Telecom Systems
  • Voltage Regulator with Accurate Current Limit
  • High Frequency Battery-Powered System
  • USB-PD Source
Part Models 1
1ku List Price Starting From $3.42

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Software and Part Ecosystem

Software and Part Ecosystem

Evaluation Kit

Evaluation Kits 1

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LT8350 | 40VIN, 18VOUT, 6A Synchronous Buck‑Boost Silent Switcher®



LT8350 | 40VIN, 18VOUT, 6A Synchronous Buck‑Boost Silent Switcher®

LT8350 | 40VIN, 18VOUT, 6A Synchronous Buck‑Boost Silent Switcher®

Product Detail

Evaluation circuit EVAL-LT8350-AZ is a 40V synchronous buck-boost converter featuring the LT8350. It drives up to 2.5A load at 12V output when VIN is between 9V and 40V and will run down to 3VIN with reduced output current. EVAL-LT8350-AZ runs at 350kHz switching frequency with spread spectrum frequency modulation (SSFM) disabled. When enabled, SSFM spreads the switching frequency of the LT8350 from fSW to fSW +25% for reduced EMI emission.

The LT8350 has an operating input voltage range of 3V to 40V. It has internal, synchronous 42V MOSFETs at buck-side and 20V MOSFETs at boost-side for high efficiency and small size. It has an adjustable switching frequency between 200kHz and 2MHz. The LT8350 can be synchronized to an external source, programmed with SSFM enabled for low EMI, or set to normal operation.

The LT8350’s integrated LOADTG high side PMOS driver assists with disconnecting load when a fault is triggered. LOADTG turns off the PMOS when FB < 0.25V or FB > 1.1V or ISP–ISN > 0.75V. LOADEN can be used directly to turn off LOADTG and all power switches.

The LT8350 can regulate output current using ISP and ISN. Maximum load current can be limited when LT8350 is used for a constant voltage regulator. It can be also used for a LED driver or a battery charger where constant current regulation is required. Output current can be adjusted by placing a controllable DC voltage on the CTRL pin.

The output current can be monitored through the ISMON output pin. ISMON can be used to improve load transient response by injecting load current to VC. The load current injection is described in the following sections.

Undervoltage lockout can be adjusted on EVAL-LT8350-AZ with a few simple resistor choices.

Small ceramic input and output capacitors are used to save space and cost. The board is designed with tiny, high frequency capacitors placed near the VIN and VOUT pins for a reduction in radiated EMI.

There is an inductor EMI filter and a small ferrite bead EMI filter on the input and output of EVAL-LT8350-AZ. These filters, combined with proper board layout and SSFM, are effective in reducing EMI to pass CISPR25 class 5 conducted EMI. Please follow the recommended layout and four-layer PCB thickness of EVAL-LT8350-AZ for low EMI applications.

The LT8350 data sheet gives a complete description of the part, operation, and applications information. The data sheet must be read in conjunction with the demo manual for EVAL-LT8350-AZ. The LT8350RV is assembled in a 32-lead laminate package with QFN footprint (LQFN) with thermally enhanced exposed ground pads. Proper board layout is essential for maximum thermal performance.

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.

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.

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