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”.
