LT8374/
LT8374-1

Evaluation board EVAL-LT8374-AZ is a synchronous stepdown LED driver featuring the LT8374. It drives up to 36V of LEDs at 1.2A when the EMIVIN terminal is between 42V and 57V. EVAL-LT8374-AZ runs at 330kHz switching frequency and features options for spread-spectrum frequency modulation (SSFM) or external synchronization.

The LT8374 has an input voltage range of 6.5V to 60V. It features 60V synchronous internal power switches for high efficiency and small solution size. The switching frequency of LT8374 is fixed at 330kHz, and the device can be synchronized with an external clock source or configured with internal SSFM for low EMI. With SSFM enabled, the LT8374 modulates its switching frequency between 330kHz and 410kHz to reduce switching emissions. EVALLT8374- AZ includes a SYNC/SSFM jumper to configure the LT8374 for either external synchronization, SSFM, or set to normal operation.

The LT8374 can be analog dimmed by applying a DC voltage between 1.25V and 250mV to the CTRL pin. An internal 20μA current source allows for a single resistor connected between the CTRL pin and GND to provide this voltage. Alternatively, the LT8374 can be analog dimmed by applying a 15kHz to 200kHz PWM signal with a duty cycle between 12.5% to 62.5% to the CTRL pin. For higher-resolution LED brightness control, a 100Hz to 200Hz PWM signal can be applied to the CTRL pin.

Small ceramic input and output capacitors are used to save space and cost. This evaluation board is designed with high frequency capacitors placed close to the IC’s VIN pins to form a compact switching hotloop for best EMI performance. Ferrite bead filters placed at the input and output help further reduce switching emissions. For best efficiency, the EMI filters at the input and output can be removed. Please follow the recommended layout and the four-layer PCB thickness of EVAL-LT8374-AZ for optimal performance.

The LT8374 features overvoltage protection (OVP) which uses the IC’s constant voltage regulation loop to regulate the output to approximately 40V in the case of an OPENLED event. A single resistor connecting VOUT to FB provides this regulation setpoint. Both LED current and output overvoltage protection (OVP) can all be adjusted with simple modifications to EVAL-LT8374-AZ.

The LT8374 also features optional internal compensation options for reduced component-count designs. To utilize the internal compensation options, the external compensation components must be removed, and the VC pin must be left floating. With external compensation components removed, the CAP pin can either be left floating or connected to GND to select between the two internal compensation options. EVAL-LT8374-AZ is configured with an optimized external compensation network by default and includes a jumper for selecting between the two internal and external compensation configurations.

The LT8374 data sheet gives a complete description of the device, its operation, and applications information. The data sheet must be read in conjunction with the demo manual for the evaluation board EVAL-LT8374-AZ. The LT8374 is assembled in a 16-lead plastic QFN package with a thermally enhanced exposed ground pad. The proper board layout is essential for maximum performance. Refer to the “Designing the Printed Circuit Board” section in the data sheet.

Evaluation board EVAL-LT8374-1-AZ is a synchronous step-down LED driver featuring the LT8374-1. It drives up to 15V of LEDs at 1A when the EMIVIN terminal is between 18V and 47V. EVAL-LT8374-1-AZ runs at 2MHz switching frequency and features options for spread-spectrum frequency modulation (SSFM) or external synchronization.

The LT8374-1 has an input voltage range of 6.5V to 60V. It features 60V synchronous internal power switches for high efficiency and small solution size. The switching frequency of LT8374-1 is fixed at 2MHz, and the device can be synchronized with an external clock source or configured with internal SSFM for low EMI. With SSFM enabled, the LT8374-1 modulates its switching frequency between 2MHz and 2.5MHz to reduce switching emissions. EVAL-LT8374-1-AZ includes a SYNC/SSFM jumper to configure the LT8374-1 for either external synchronization, SSFM, or set to normal operation.

The LT8374-1 can be analog dimmed by applying a DC voltage between 1.25V and 250mV to the CTRL pin. An internal 20μA current source allows for a single resistor connected between the CTRL pin and GND to provide this voltage. Alternatively, the LT8374-1 can be analog dimmed by applying a 15kHz to 200kHz PWM signal with a duty cycle between 12.5% to 62.5% to the CTRL pin. For higher-resolution LED brightness control, a 100Hz to 200Hz PWM signal can be applied to the CTRL pin.

Small ceramic input and output capacitors are used to save space and cost. This evaluation board is designed with high frequency capacitors placed close to the IC’s VIN pins to form a compact switching hotloop for best EMI performance. Ferrite bead filters placed at the input and output help further reduce switching emissions. For best efficiency, the EMI filters at the input and output can be removed. Follow the recommended layout and the fourlayer PCB thickness of EVAL-LT8374-1-AZ for optimal performance.

The LT8374-1 features overvoltage protection (OVP) which uses the IC’s constant voltage regulation loop to regulate the output to approximately 20V in the case of an OPENLED event. A single resistor connecting VOUT to FB provides this regulation setpoint. Both LED current and output overvoltage protection (OVP) can all be adjusted with simple modifications to EVAL-LT8374-1-AZ.

The LT8374-1 also features optional internal compensation options for reduced component-count designs. To utilize the internal compensation options, the external compensation components must be removed, and the VC pin must be left floating. With external compensation components removed, the CAP pin can either be left floating or connected to GND to select between the two internal compensation options. EVAL-LT8374- 1-AZ is configured with an optimized external compensation network by default and includes a jumper for selecting between the two internal and external compensation configurations.

The LT8374-1 datasheet gives a complete description of the device, its operation, and applications information. The datasheet must be read in conjunction with this demo manual for evaluation board EVAL-LT8374-1-AZ. The LT8374-1 is assembled in a 16-lead plastic QFN package with a thermally-enhanced exposed ground pad. Proper board layout is essential for maximum performance. See the datasheet section “Designing the Printed Circuit Board”.