DC1122A - Demo Manual

DEMO CIRCUIT 1122
QUICK START LT3681
GUIDE
LT3681
Step-Down Regulator
DESCRIPTION
Demonstration circuit 1122 features
LT3681 in a 500kHz step-down converter circuit, designed for 3.3V
output from a 4.5V to 34V input.
The wide input range of the LT3681
allows a variety of input sources.
The typical sources are automotive
batteries, wall adaptors and industrial supplies. The current mode
control scheme creates fast transient response and good loop stability. In addition, the LT3681’s
integrated boost diode and catch
diode reduce the parts count. The
low ripple Burst Mode Operation of
LT3681 not only allows the circuit
to have high efficiency over a
broad current range but also provides the low output ripple at
light load conditions. The RUN/SS
pin can be used to set the part in
micropower
shutdown
mode.
The
RUN/SS pin can also be used to program soft start. In this mode, the
RUN/SS pin is driven through an external RC filter to create a voltage ramp on this pin. The soft
start function reduces the input
current surge during start-up.
The LT3681 datasheet gives a complete description of the part, operation and application information. The datasheet must be read in
conjunction with this quick start
guide for demo circuit 1122.
Design files for this circuit board
are available. Call the LTC factory.
, LTC and LT are registered trademarks of Linear Technology Corporation. ThinSOT and PowerPath are trademarks of Linear Technology Corporation.
Performance Summary for Step-Down Regulator ( TA = 25oC )
PARAMETER FOR BUCK REGULATOR
Minimum Input Voltage
Maximum Input Voltage
Output Voltage VOUT
Maximum Output Current
Typical Switching Frequency
CONDITION
VALUE
4.5V
34V
3.3V +/- 4%
2A
500kHz
QUICK START PROCEDURE
Demonstration circuit 1122 is easy
to set up to evaluate the performance of the LT3681. Refer to
Figure 1 for proper measurement
equipment setup and follow the procedure below:
1
LT3681
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 Vin or Vout
and GND terminals. See Figure 2 for proper
scope probe technique.
NOTE. Make sure that the input voltage
does not exceed the maximum input
voltage.
4. Check
for
voltages.
the
proper
output
1. Place JP1 on the RUN position:
NOTE. If there is no output, temporarily
disconnect the load to make sure that
the load is not set too high.
2. With power off, connect the in-
5. Once the proper output voltage
put power supply to Vin and GND.
3. Turn on the power at the input.
is established, adjust the load
within the operating range and
observe the output voltage regulation, ripple voltage, efficiency and other parameters.
Figure 1. Proper Measurement Equipment Setup
GND
VIN
Figure 2. Measuring Input or Output Ripple
2
LT3681
3
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