DEMO MANUAL DC1533A
LTM8045
Inverting/SEPIC µModule Converter
with Up to 700mA Output
DESCRIPTION
Demo circuit DC1533A features the LTM
®
8045, an inverting/
SEPIC μModule converter delivering up to 700mA of output
current. DC1533A is configured as an inverting converter,
but can be easily changed to a SEPIC configuration for
non-inverting step-up or step-down functionality. The
user adjustable features of the LTM8045 such as output
voltage, switching frequency, soft-start period and under-
voltage lockout can be changed on DC1533A simply by
modifying or installing the appropriate resistors or capaci-
tor. The LTM8045 data sheet must be read in conjunction
with this demo manual to properly use or modify demo
circuit DC1533A.
Design files for this circuit board are available at
http://www.linear.com/demo
L,
LT, LTC, LTM, μModule, 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
PARAMETER
Minimum Input Voltage, V
IN
Maximum Input Voltage, V
IN
Regulator Output Voltage, V
OUT–
Maximum Output Current, I
OUT–
Efficiency
Switching Frequency
(T
A
= 25°C)
MIN
18
TYP
MAX
2.8
UNITS
V
V
–5.19
V
mA
mA
80
700
%
kHz
CONDITIONS
R2 = 60.4k
V
IN
= 5V
V
IN
= 12V
V
IN
= 5V, I
OUT–
= 400mA
R1 = 130k
–4.83
430
580
BOARD PHOTO
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DEMO MANUAL DC1533A
QUICK START PROCEDURE
Demo circuit DC1533A is an easy way to evaluate the
performance of the LTM8045. Refer to Figure 1 for the
proper measurement equipment setup and Figure 2 for
the maximum output current versus input voltage, then
follow the procedure below:
NOTE: Do not hot-plug the V
IN
terminal at high input volt-
ages. Hot-plugging a power supply through wire leads
to the demonstration circuit can cause the voltage on
the extremely low ESR ceramic input capacitor to ring to
twice its DC value. In order to protect the LTM8045, an
aluminum electrolytic capacitor with higher ESR is placed
at the input terminals. This may protect against some, but
not all, input transients due to a hot-plugged power supply.
See Application Note 88 for more details.
NOTE: When measuring the input or output voltage ripple,
care must be taken to avoid a long ground lead on the
oscilloscope probe. Measure the input or output voltage
ripple by touching the probe tip directly across the V
IN
or
V
OUT
and GND terminals. See Figure 3 for proper scope
probe technique.
1. Place JP1 in the ON position.
2. Connect the power supply (with power off), load, and
meters as shown in Figure 1.
3. After all connections are made, turn on the input power
and verify that the output voltage is –5V.
NOTE: If the output voltage is too low, temporarily discon-
nect the load to make sure that the load is not set too high.
4. Once the proper output voltage is established, adjust
the load within the operating range and observe the
output voltage regulation, ripple voltage, efficiency and
other parameters.
NOTE: See the section that follows for instructions to
convert DC1533A to a 5V
OUT
SEPIC with a positive V
OUT
.
Figure 1. Proper Measurement Equipment Setup
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DEMO MANUAL DC1533A
Instructions to Convert DC1533A to a 5V
OUT
SEPIC with a Positive V
OUT
1. Start with DC1533A. Disconnect all supplies and loads.
2. Remove R2 and install R3 = 45.3k as shown in Figure 4. R3 MUST BE PRESENT BEFORE OPERATION OTHERWISE
THE LTM8045 MAY BE DAMAGED.
Figure 4
3. Make three cuts on the top copper to separate the terminal labeled GND from the ground plane, as shown in
Figure 5. The terminal labeled GND is now V
OUT+
.
Figure 5
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