Evaluation board EVAL-LT8376-AZ is a 60V, 2A synchronous Buck LED driver featuring the LT8376. EVAL-LT8376-AZ drives a single string of LEDs up to 36V at 1.5A when VIN is between 43V and 57V. EVAL-LT8376-AZ has an undervoltage lockout (UVLO) set at 40V with 2V hysteresis for turn-on. EVAL-LT8376-AZ runs at 350kHz switching frequency and features optional spread spectrum modulation (SSFM). With SSFM enabled, LT8376 modulates its switching frequency from fSW to fSW + 25% to reduce EMI emissions.
The LT8376 has an input voltage range of 3.6V to 60V. LT8376 has internal, synchronous 60V switches for high efficiency and small size. LT8376 has an adjustable switching frequency between 200kHz and 2MHz. The LT8376 can be synchronized with an external clock source or configured with SSFM enabled for low EMI. EVAL-LT8376-AZ includes a SYNC/SSFM jumper to configure the LT8376 for either external frequency synchronization, SSFM enabled for low EMI, or set to normal operation with SSFM disabled.
The LT8376’s integrated PWMTG high-side PMOS driver assists with PWM dimming of the connected LEDs. The LED string can be PWM dimmed for accurate brightness control with an externally generated PWM signal or an internally-generated PWM signal. EVAL-LT8376-AZ has jumpers that can be set to switch between internally-generated PWM signal, externally generated PWM signal, and 100% on with no PWM signal. The LT8376 can also be analog dimmed by placing a controllable DC voltage on the CTRL pin. When running PWM dimming with SSFM enabled, the SSFM aligns itself with the PWM signal for flicker-free operation of the LED string. This applies to both internal and external PWM dimming.
Small ceramic input and output capacitors are used to save space and cost. The input and output filters on EVAL-LT8376-AZ reduce its EMI. The filters consist of a small ferrite bead or inductor and high frequency ceramic capacitors. These filters, combined with proper board layout and SSFM, are very effective in reducing EMI to comply with CISPR25 class 5 limits. Please follow the recommended layout and the four-layer PCB thickness of EVAL-LT8376-AZ. For best efficiency and PWM dimming performance, the EMI filters at the input and output can be removed.
The open LED overvoltage protection (OVP) uses the IC’s constant voltage regulation loop to regulate the output to approximately 41V if the LED string is opened. The output current can be monitored through the ISMON pin. Also, the FAULT pin can be used for open and short detection.
The input undervoltage lockout (UVLO), LED current, output overvoltage protection (OVP), and switching frequency, can all be easy adjusted with simple modifications to EVAL-LT8376-AZ.
The LT8376 data sheet gives a complete description of the device, operation, and applications information. The data sheet must be read in conjunction with this demo manual for evaluation board EVAL-LT8376-AZ. The LT8376RV is assembled in a 28-lead plastic LQFN package with a thermally enhanced exposed ground pad. Proper board layout is essential for maximum performance. See the data sheet section “Designing the Printed Circuit Board”.
