DESCRIPTION
Evaluation board EVAL-LT8376-AZ is a 60V, 2A synchronous
Buck LED driver featuring the LT®8376. EVALLT8376-
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. EVALLT8376-
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”.