Analog Devices DC2575A Demo Manual

DESCRIPTION
Demonstration circuit DC2575A is a 60V 2MHz synchro-
nous buck-boost LED driver featuring the LT8391A. It
accepts an input voltage from 4V to 60V and drives a
single string of LEDs up to 16V at 1.5A. DC2575A runs at
2MHz switching frequency and features spread spectrum
frequency modulation (SSFM) which can be enabled with
a simple jumper. SSFM spreads the switching frequency
from f to f +25% for reduced EMI. SSFM is not nec-
SW SW
essary in applications where EMI is not important.
DC2575A uses AEC-Q automotive-approved components
such as power MOSFETs, diodes, input and output capaci-
tors and inductors.
The LT8391A has an adjustable switching frequency
between 600kHz and 2MHz. The jumper also allows exter-
nal frequency synchronization.
The LT8391A can be PWM dimmed with an external PWM
signal and an internally-generated PWM signal. DC2575A
has a jumper that can be set to switch between internally-
generated PWM signal, externally-generated PWM signal,
and no PWM signal (100% on). It can be analog dimmed
with a control voltage on either of its two control pins.
When run with both PWM dimming and spread spectrum,
the spread spectrum aligns itself with the PWM signal for
flicker-free operation.
The LT8391A features both open LED and short LED
+
(LED to GND) protection as well as a fault output flag.
DEMO MANUAL DC2575A
60V 2MHz Synchronous
1.5A Buck-Boost LED Driver
Small ceramic input and output capacitors are used to
save space and cost. The board is designed with capaci-
tors on both sides of the synchronous switches for a
reduction in radiated EMI. The open LED overvoltage
protection uses the IC's constant voltage regulation loop
to regulate the output to approximately 18V if the LED
string is opened. There is a protection diode from LED
to GND to prevent negative ringing during a short-circuit
with long wires.
Undervoltage lockout can be adjusted on the circuit with
a few simple resistor choices.
EMI filters and gate resistors on the demo circuit reduce
this high power converter's EMI below CISPR 25 Class 5
limits. This is intended for automotive applications where
CISPR 25 EMI standards are observed. In non-automotive
applications, where EMI may not be as important, the
input and output filters as well as the gate resistors can
be removed for higher efficiency. Please note the optional
EMI components in the parts list.
The LT8391A data sheet gives a complete description of
the part, operation and applications information. The data
sheet must be read in conjunction with this Demo Manual
for demonstration circuit DC2575A. The LT8391AIFE is
assembled in a 28-lead plastic TSSOP (FE) package with
a thermally-enhanced ground pad. Proper board layout
is essential for maximum thermal performance. See the
data sheet section "Layout Considerations".
Design files for this circuit board are
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LT8391AIFE
+
available.
Rev. A
1