LT8350S

• 3V–40V Operating Input Voltage
  • Reduced EMI emissions for CISPR 25 Class 5
  • Spread Spectrum Frequency Modulation
  • Input and Output EMI filter
  • In-built Input and Output high-frequency capacitors
• Adjustable UVLO, V_OUT, f_SW, Output Current andLimit
• Voltage-Monitoring (PGOOD) and Current-Monitoring(ISMON)
• Configurable SYNC pin for Forced Continuous Mode(FCM), Discontinuous Conduction Mode (DCM),SSFM, and external Frequency Synchronization
• Feed Forward Function for improved transient response

The EVAL-LT8350S-AZ Evaluation board is a 40V synchronous buck-boost converter featuring the LT^®8350S. 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-LT8350S-AZ runs at 350kHz switching frequency with spread spectrum frequency modulation (SSFM) disabled. When enabled, SSFM spreads the switching frequency of the LT8350S from fSW to fSW + 25% for a reduced electromagnetic interference (EMI) emission.

The LT8350S has an operating input voltage range of 3V to 40V. It has internal, synchronous 42V MOSFETs on the buck side and 20V MOSFETs on the boost side for high efficiency and small size. It has an adjustable switching frequency between 200kHz and 2MHz. The LT8350S can be synchronized to an external source, programmed with SSFM enabled for low EMI, or set to normal operation.

The LT8350S’ 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 LT8350S can regulate output current using ISP and ISN. Maximum load current can be limited when LT8350S is used for a constant voltage regulator. It can also be used for an 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.

An Undervoltage lockout can be adjusted on EVAL-LT8350S-AZ with a few simple resistor choices.

Small ceramic input and output capacitors are used to save space and cost. Although LT8350S has in-built high-frequency capacitors(100nF) on the input and output, the board is designed with tiny, high-frequency capacitors placed near the V_IN and V_OUT pins for added flexibility.

There is an inductor EMI filter and a small ferrite bead EMI filter on the input and output of EVAL-LT8350S-AZ. These filters, combined with proper board layout and SSFM, are effective in reducing EMI to pass CISPR25 class 5 conducted EMI. Follow the recommended layout and four-layer printed circuit board (PCB) thickness of EVAL-LT8350S-AZ for low EMI applications.

The LT8350S data sheet provides a complete description of the part, operation, and applications information. The data sheet must be read in conjunction with this demo manual for EVAL-LT8350S-AZ. The LT8350S 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.

Design files for this circuit board are available at Product Evaluation Boards and Kits | Design Center | Analog Devices.