Description
DEMO MANUAL DC2565A
LT8607
42V, 0.75A Micropower Synchronous
Step-Down Regulator
Demonstration Circuit 2565A is a 42V, 0.75A micropower
synchronous step-down regulator featuring the LT®8607.
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 supplies. The LT8607
is a compact, high efficiency,
high speed synchronous monolithic step-down switching regulator that consumes less than 3μA of quiescent
current when output is regulated at 5V. Top and bottom
power switches, compensation components and other
necessary circuits are inside of the LT8607 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, VCC is applied to the SYNC pin for low
EMI spread spectrum operation. To synchronous 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. The radiated
EMI performances of the board (with EMI filter) are shown
in Figure 2 and Figure 3. The red lines in Figure 2 and
Figure 3 are CISPR25 Class 5 peak limit. To use the EMI
filter, the input should be tied to V
, not VIN. An induc-
EMI
tor 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 LT8607 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 DC2565A.
Design files for this circuit board are available at
http://www.linear.com/demo/DC2565A
L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks
of Analog Devices, Inc. All other trademarks are the property of their respective owners.
performance summary
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
V
IN
V
OUT
I
OUT
f
SW
EFE Efficiency at DC V
Input Voltage Range 5.5 42 V
Output Voltage 4.8 5 5.2 V
Maximum Output Current 0.75 A
Switching Frequency 1.85 2 2.15 MHz
Specifications are at TA = 25°C
= 12V, I
IN
= 0.75A 92.4 %
OUT
dc2565af
1
DEMO MANUAL DC2565A
DC2565A F01
Quick start proceDure
DC2565A is easy to set up to evaluate the performance
of the LT8607. Refer to Figure 4 for proper measurement
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/0.75A.
Then turn off the supply.
2. With power off, connect the supply to the input termi-
nals V
and GND.
IN
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 0.75A at 5V to the
output terminals V
and GND. Set the current for 0A.
OUT
a. If efficiency measurements are desired, an ammeter
can be put in series with the output load in order to
measure the DC2565A’s output current.
b. A voltmeter can be placed across the output ter-
minals 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 established again,
adjust the load and/or input within the operating range
and observe the output voltage regulation, ripple voltage, 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
position). Please ensure that the chosen RT sets the
LT8607 switching frequency to equal or below the lowest SYNC frequency. See the Synchronization section
in the data sheet.
Figure 1. Efficiency vs Load Current at 2MHz Switching Frequency
2
100
95
90
85
80
75
70
EFFICIENCY
65
60
55
50
0
0.3 0.45 0.6 0.75
0.15
I
OUT
(A)
VIN = 12V
= 24V
V
IN
dc2565af
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