DESCRIPTION
Demonstration circuit 897 is a monolithic step-dow n
DC/DC sw itching regulator featuring the LT3493. The
demo board is designed for 3.3V output from a 4.5V to
36V input. The w ide input range of the LT3493 allow s a
variety of input sources. The typical sources are automo-
tive batteries, w all adaptors and industrial supplies. The
750kHz sw itching frequency allow s the use of small, low
cost inductor and ceramic capacitors, resulting in low ,
predictable output ripple. The current mode control
scheme creates fast transient response and good loop
stability. The internal compensation reduces the compo-
nent count and solution size. The gate drive of the inter-
nal sw itch is boosted to a voltage that is higher than the
Vin to ensure saturation of the sw itch. A charge pump
consisting of diode and a capacitor on the demo board
performs the boost function. The SHDN pin can be used
to set the part in micropow er shutdow n mode, reducing
the supply current to less than 2uA. The SHDN pin can
also be used to program soft start. In this mode, the
SHDN pin is driven through an external RC filter to create
a voltage ramp on this pin. The soft start function re-
duces the input current surge during start-up. Cycle by
cycle current limit, frequency foldback and thermal shut-
dow n provide protection against shorted outputs.
The LT3493 datasheet gives a complete description of
the part, operation and application information. The data-
sheet must be read in conjunction w ith this quick start
guide for demo circuit 897.
Design files for this circuit board are available. Call
the LTC factory.
, LTC and LT are registered trademarks of Linear Technology Corporation. ThinSOT and
Pow erPath are trademarks of Linear Technology Corporation.
Performance Summary ( T
A
= 25
o
C )
PAR AM ETER FOR LED DRIVER CONDITION VALUE
Minimum input voltage 4.5V
Maximum input voltage 36V
Output voltage V
OU T
3.3V
+/- 4%
Maximum output current V
IN
=4.5V 950mA
Maximum output current V
IN
=8V 1.2A
Typical sw itching frequency 750kHz
QUICK START PROCEDURE
Demonstration circuit 897 is easy to set up to evaluate
the performance of the LT3493. R efer to Figure 1 for
proper measurement equipment setup and follow the
procedure below :
NOTE.
W hen 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.
1.
Place JP1 on the RUN position
:
2.
W ith pow er off, connect the input pow er supply to Vin
and GN D.
3.
Turn on the pow er at the input.
NOTE.
Make sure that the input voltage does not exceed 36V.
4.
Check for the proper output voltages.
NOTE.
If there is no output, temporarily disconnect the load to make
sure that the load is not set too high.
1.2A, 750KHz Step-down Switching Regula
in 2mm
×
