DC1221A - Demo Manual

DE M O CIR CU IT 1221
Q U ICK S TA R T GLT3502
U IDE
LT3 5 0 2
1.1M H z , 5 0 0 m A , S te p -d o w n R e g u la to r in
2m m ×2m m DF N
DESCRIPTION
Demonstration circuit 1221 is a monolithic step-dow n
DC/DC sw itching regulator featuring the LT3502. The
demo circuit is designed for 3.3V output from a 5V to
40V input. The w ide input range of the LT3502 allow s
a variety of input sources including automotive batteries and 24V industrial supplies. The high sw itching
frequency allow s the use of tiny, low cost external
components. The current mode control scheme creates fast transient response and good loop stability.
The boost diode is internal 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 R C 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 protection
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
datasheet must be read in conjunction w ith this quick
start guide for demo circuit 1221.
D esign files for this circuit board are available. Call
the LTC factory.
,LTC and LT are registered trademarks ofLinear Technology Corporation.
Perform ance Sum m ary (TA = 25oC)
PAR AM ETER
Minimum Input Voltage
Maximum Input Voltage
O utput Voltage VOUT
Sw itching Frequency
Maximum O utput Current
Efficiency
Voltage R ipple
CO N D ITIO N
VIN = 12V,IOUT = 500mA
VIN = 12V,IOUT = 500mA
VALU E
5V
40V
3.328V ±2.8%
1.1MH z ±18%
500mA
82%
5mV
Q U ICK STA RT PROCEDU RE
Demonstration circuit 1221 is easy to set up to evaluate the performance of the LT3502. 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 O N position.
2. W ith pow er off,connect the input pow er supply to Vin
and GND.
3. Turn on the pow er at the input.
NOTE. Make sure that the input voltage does not exceed 40V.
4. Check for the proper output voltages.
NOTE. Ifthere is no output,temporarily disconnect the load to make sure
that the load is not set too high.
5. Once the proper output voltage is established, adjust
the load w ithin the operating range and observe the
1
LT3502
output voltage regulation, ripple voltage, efficiency
and other parameters.
Figure 1. Proper M easurem entEquipm entSetup
GND
VIN
Figure 2. M easuring Inputor OutputR ipple
2
LT3502
3
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