DC1050A - Demo Manual

DEMO CIRCUIT 1050
LT3503
QUICK START GUIDE
LT3503
1.2A, 2.2MHz Step-Down Switching Regulator
in 2mm×3mm DFN
DESCRIPTION
Demonstration circuit 1050 is a monolithic step-dow n
DC/DC sw itching regulator featuring LT3503. The demo
board is designed for 3.3V output from a 4.5V to 20V
input. The w ide input range of the LT3503 allow s a variety of input sources. The typical sources are automotive
batteries, w all adaptors and industrial supplies. The
2.2M H z 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 component count and solution size. The gate drive of the internal 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 a diode and capacitor on the demo board
performs the boost function. The SH DN pin can be used
to set the part in micropow er shutdow n mode, reducing
the supply current to less than 2uA. The SH DN pin can
also be used to program soft start. In this mode, the
SH DN 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, frequency foldback and thermal shutdow n provide the protection against shorted outputs.
The LT3503 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 1050.
Design files for this circuit board are available. Call
the LTC factory.
,LTC and LT are registered trademarks ofLinear Technology Corporation. ThinSOT and
Pow erPath are trademarks ofLinear Technology Corporation.
Performance Summary ( TA = 25oC )
PAR AM ETER FO R STEP-DO W N CON VERTER
M inimum input voltage
M aximum input voltage
O utput voltage VOUT
M aximum output current
M aximum output current
Typical sw itching frequency
CO N DITIO N
VALU E
4.5V
20V
3.3V +/- 4%
1A
1.2A
2.2M H z
VIN = 5.5V
VIN = 8.5V
QUICK START PROCEDURE
Demonstration circuit 1050 is easy to set up to evaluate
the performance of the LT3503. 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. M easure 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 in the R U N position:
2.
W ith pow er off,connect the input pow er supply to Vin
and G N D.
3.
Turn on pow er at the input.
NOTE. M ake sure that the input voltage does not exceed 20V.
4.
Check for proper output voltages.
NOTE. Ifthere is no output,temporarily disconnect the load to make
sure that the load is not set too high.
1
LT3503
O nce the proper output voltages are established, adjust the loads w ithin the operating range and observe
A
_+
_
_
+
+
V
the output voltage regulation, ripple voltage, efficiency
and other parameters.
Load
A
V
_
+
_
5.
+
_ +
Figure 1. Proper M easurem ent Equipm ent Setup
GND
VIN
Figure 2. M easuring Input or Output Ripple
2
LT3503
3
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