1
dc2195bf
DEMO MANUAL DC2195B
DESCRIPTION
LT8609/LT8609A
42V, 2A Micropower Synchronous
Step-Down Regulator
Demonstration circuit 2195B is a 42V, 2A micropower
synchronous step-down regulator featuring the
LT8609/
LT8609A
. There are two assembly versions. DC2195B-A
is for the LT8609A and DC2195B-B is for the LT8609.
The difference is the LT8609A has slower edge speeds
for improved EMI at the expense of a small efficiency loss.
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 LT8609/LT8609A 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 LT8609 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
L
, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
PERFORMANCE SUMMARY
spectrum operation. To synchronize to an external clock,
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. Under spread
spectrum operation, 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.
This board is suitable for a wide range of automotive,
telecom, industrial, and other general purpose applications.
The LT8609/LT8609A data sheet gives a complete descrip-
tion of the part, operation and application information. The
data sheet must be read in conjunction with this demo
manual for DC2195B.
Design files for this circuit board are available at
http://www.linear.com/demo/DC2195B
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
2
A
f
SW
Switching Frequency
1.85
2
2.15
MHz
EFE (LT8609A)
Efficiency for DC2195B-A
V
IN
= 12V, I
OUT
= 1A
92.1
%
EFE (LT8609)
Efficiency for DC2195B-B
V
IN
= 12V, I
OUT
= 1A
92.9
%
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