1
dc2458af
DEMO MANUAL DC2458A
DESCRIPTION
LT8608
42V, 1.5V Micropower Synchronous
Step-Down Regulator
Demonstration circuit 2458A is a 42V, 1.5A micropower
synchronous step-down regulator featuring the
.
The demo board is designed for 5V output from a 5.5V to
42V input. The wide input range allows a variety of input
sources, such as automotive batteries and industrial sup-
plies. The LT8608 is a compact, high efficiency, high speed
synchronous monolithic step-down switching regulator
that consumes only 2.5μA of quiescent current when
output is regulated at 5V. Top and bottom power switches,
compensation components and other necessary circuits
are inside of the LT8608 to minimize external components
and simplify design.
The SYNC pin on the demo board is grounded by default
for low ripple Burst Mode
®
operation. Move JP1 to PULSE
SKIPPING position can change the operation mode to pulse-
skipping operation. Once JP1 is on SPREAD SPECTRUM
position, V
CC
is applied to the SYNC pin for low EMI spread
spectrum operation. To synchronous to an external clock,
L
, LT, LTC, LTM, Linear Technology, Burst Mode and the Linear logo are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
PERFORMANCE SUMMARY
move JP1 to SYNC and apply the external clock to the
SYNC turret. Figure 1 shows the efficiency of the circuit.
The demo board has an EMI filter installed. The radiated
EMI performances of the board (with EMI filter) are shown
in Figures 2 and 3. The red lines in Figures 2 and 3 are
CISPR25 class 5 peak limit. To use the EMI filter, the input
should be tied to VEMI, not V
IN
. An inductor L2, which is
a 0Ω jumper on the board by default now, can be added
in the EMI filter to further reduce the conducted emission.
The LT8608 data sheet gives a complete description of
the part, operation and application information. The data
sheet must be read in conjunction with this demo manual
for DC2458A.
Design files for this circuit board are available at
http://www.linear.com/demo/DC2458A
Specifications are at T
A
= 25°C
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
IN
Input Voltage Range
5.5
42
V
V
OUT
Output Voltage
4.8
5
5.2
V
I
OUT
Maximum Output Current
1.5
A
f
SW
Switching Frequency
1.85
2
2.15
MHz
EFE
Efficiency at DC
V
IN
= 12V, I
OUT
= 0.75A
92.2
%
