LT3757
1
DESCRIPTION
Demonstration circuit 1548A features
LT3757EDD in a 300kHz CUK converter circuit,
designed for -15V output from a 7V to 28V in-
put.
The LT3757EDD operates over an input range
of 2.9V to 40V, suitable for applications from
single-cell lithium-ion battery portable electron-
ics up to high voltage automotive and industrial
power supplies. It also exhibits low shutdown
quiescent current of 1µA, making them an ideal
fit for battery-operated systems. Thanks to a
novel FBX pin architecture, the LT3757EDD can
be connected directly to a divider from either the
positive output or the negative output to ground.
It also packs many popular features such as
soft-start, input undervoltage lockout, adjustable
frequency and synchronization in a small 10-
lead MSOP package or a 3mm × 3mm QFN
package.
The LT3757EDD datasheet gives a complete
description of the part, operation and application
information. The datasheet must be read in con-
junction with this quick start guide for demo cir-
cuit 1548A.
Design files for this circuit board are avail-
able. Call the LTC factory.
LT, LTC and are registered trademarks of Li-
near Technology Corporation. All other trade-
marks are the property of their respective own-
ers.
Table 1. Performance Summary for 300kHz CUK Regulator ( TA = 25
o
C )
PARAMETER CONDITION VALUE
Minimum Input Voltage 7V
Maximum Input Voltage 28V
Output Voltage V
OUT
-15V +/-3%
Maximum Output Current 1A
Typical Switching Frequency 300kHz
QUICK START PROCEDURE
Demonstration circuit 1548A is easy to set up
to evaluate the performance of the
LT3757EDD. Refer to Figure 1 for proper
measurement equipment setup and follow the
procedure below:
NOTE.
When measuring the input or output volt-
age ripple, care must be taken to avoid a long
ground lead on the oscilloscope probe. Meas-
ure the input or output voltage ripple by touch-
ing the probe tip directly across the Vin or Vout
and GND terminals. See Figure 2 for proper
scope probe technique.
1.
Place JP1 on the ON position.
2.
With power off, connect the input power
supply to Vin and GND.
3.
Turn on the power at the input.
NOTE.
Make sure that the input voltage does
not exceed the maximum input voltage.
4.
Check for the proper output voltages.
NOTE.
If there is no output, temporarily dis-
connect the load to make sure that the load
is not set too high.
Once the proper output voltages are estab-
lished, adjust the loads within the operating
DEMO CIRCUIT 1548A
QUICK START GUIDE
LT3757
EDD
HIGH EFFICIENCY CUK CONVERTER
LT3757
2
range and observe the output voltage regula-
tion, ripple voltage, efficiency and other pa-
rameters.
Figure 1. Proper Measurement Equipment Setup
Figure 2. Measuring Input or Output Ripple
Supply
Power
V
A
Vin
+
-
+
-
+
-
V
Vout +
-
Iin
A+
-Iout
Load
+
-
LT3757
3
