DEMO MANUAL DC2195B
LT8609/LT8609A
42V, 2A Micropower Synchronous
Step-Down Regulator
DESCRIPTION
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
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
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
SYMBOL
V
IN
V
OUT
I
OUT
f
SW
EFE (LT8609A)
EFE (LT8609)
PARAMETER
Input Voltage Range
Output Voltage
Maximum Output Current
Switching Frequency
Efficiency for DC2195B-A
Efficiency for DC2195B-B
Specifications are at T
A
= 25°C
CONDITIONS
MIN
5.5
4.8
2
1.85
V
IN
= 12V, I
OUT
= 1A
V
IN
= 12V, I
OUT
= 1A
2
92.1
92.9
2.15
5
TYP
MAX
42
5.2
UNITS
V
V
A
MHz
%
%
dc2195bf
1
DEMO MANUAL DC2195B
QUICK START PROCEDURE
DC2195B is easy to set up to evaluate the performance of
the LT8609/LT8609A. Refer to Figure 4 for proper measure-
ment equipment setup and follow the procedure below:
NOTE: When measuring the input or output voltage ripple,
care must be taken to avoid a long ground lead on the
oscilloscope probe. See Figure 5 for the proper scope
technique.
1. Set an input power supply that is capable of 42V/2A.
Then turn off the supply.
2. With power off, connect the supply to the input terminals
V
EMI
and GND.
3. Turn on the power at the input.
NOTE: Make sure that the input voltage never exceeds 42V.
4. Check for the proper output voltage of 5V. Turn off the
power at the input.
5. Once the proper output voltage is established, connect
a variable load capable of sinking 2A at 5V to the output
terminals V
OUT
and GND. Set the current for 0A.
100
95
90
85
EFFICIENCY (%)
80
75
70
65
60
55
50
0
0.5
1
I
OUT
(A)
1.5
LT8609A
LT8609
2
DC2195 F01
a. If efficiency measurements are desired, an ammeter
can be put in series with the output load in order to
measure the DC2195B’s output current.
b. A voltmeter can be placed across the output terminals
in order to get an accurate output voltage measurement.
6. Turn on the power at the input.
NOTE: If there is no output, temporarily disconnect the
load to make sure that the load is not set too high.
7. Once the proper output voltage is again established,
adjust the load and/or input within the operating range
and observe the output voltage regulation, ripple volt-
age, efficiency and other desired parameters.
8. An external clock can be added to the SYNC terminal
when SYNC function is used (JP1 on the SYNC posi-
tion). Please ensure that the chosen R
T
sets the LT8609/
LT8609A switching frequency to equal or below the
lowest SYNC frequency. See the data sheet section,
“Synchronization.”
Figure 1. Efficiency vs Load Current at 12V Input 2MHz Switching Frequency
dc2195bf
2
Talking
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