DC1221B
QUICK START LT3502
GUIDE
LT3502
1.1MHz, 500mA, Step-down Regulator in
2mm×2mm DFN
DESCRIPTION
Demo circuit DC1221B is a monolithic step-down DC/DC
switching regulator featuring the LT3502. The demo cir-
cuit is designed for 3.3V output from a 4.5V to 40V in-
put. The wide input range of the LT3502 allows a variety
of input sources including automotive batteries and 24V
industrial supplies. The high switching frequency allows
the use of tiny, low cost external components. The cur-
rent mode control scheme creates fast transient re-
sponse and good loop stability. The boost diode is inter-
nal to reduce component count. 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 reduces
the input current surge during start-up. Cycle by cycle
current limit and frequency foldback provide the protec-
tion against shorted outputs. DA pin can further protect
the silicon under fault conditions by sensing the diode
current.
The LT3502 datasheet gives a complete description of
the part, operation and application information. The data-
sheet must be read in conjunction with this quick start
guide for demo circuit DC1221B.
Design files for this circuit board are available. Call
the LTC factory.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Performance Summary (TA = 25oC)
PARAMETER
Minimum Input Voltage
Maximum Input Voltage
Output Voltage V
OUT
Switching Frequency
Maximum Output Current
Efficiency
Voltage Ripple
CONDITION
VALUE
4.5V
40V
3.328V ±2.8%
1.1MHz ±18%
500mA
80%
10mV
V
IN
=12V, I
out
=500mA
V
IN
=12V, I
out
=500mA
QUICK START PROCEDURE
Demonstration circuit 1221B is easy to set up to evaluate
the performance of the LT3502. Refer to Figure 1 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. 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.
2.
With
power off, connect the input power supply to Vin
and GND.
NOTE.
Make sure that the input voltage does not exceed 40V.
3.
Turn on the power at the input.
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.
Place JP1 on the ON position.
5.
Once
the proper output voltage is established, adjust
the load within the operating range and observe the
1
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