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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”.