DC1188A - Demo Manual

DEMO CIRCUIT 1188
LT3684
QUICK START GUIDE
LT3684EMSE
2A, 34V Step-Down Switching Regulator
DESCRIPTION
Demonstration circuit 1188 is a monolithic step-dow n
DC/DC sw itching regulator featuring the LT3684. The
demo circuit is designed for a 3.3V output from a 4.5V to
34V input. The w ide input range of the LT3684 allow s a
variety of input sources. The typical sources are automotive batteries, w all adaptors and industrial supplies. The
programmed 800kH 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 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. The LT3684’s integrated
boost diode reduces the parts count. The R U N /SS pin
can be used to set the part in micropow er shutdow n
mode, reducing the supply current to less than 1uA. The
R U N /SS pin can also be used to program soft start. In
this mode, the R U N /SS 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.
The LT3684 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 1188.
Design 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 for Step-dow n Sw itching Regulator (TA = 25oC )
PAR AM ETER FO R BU CK R EG U LATO R
M inimum Input Voltage
M aximum Input Voltage
O utput Voltage VOUT
M aximum O utput Current
Typical Sw itching Frequency
CO N DITIO N
VALU E
4.5V
34V
3.3V +/- 4%
2A
800kH z
QUICK START PROCEDURE
Demonstration circuit 1188 is easy to set up to evaluate
the performance of the LT3684. 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 on 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 the pow er at the input.
NOTE. M ake sure that the input voltage does not exceed the maximum
input voltage.
4.
Check for the proper output voltage.
NOTE. Ifthere is no output,temporarily disconnect the load to make
sure that the load is not set too high.
5.
O nce the proper output voltage is established, adjust
the load w ithin the operating range and observe the
output voltage regulation,ripple voltage,efficiency and
other parameters.
1
LT3684
A
A
+
+
_
+
V
_
+
_V
+
Load
_
_
Figure 1. Proper M easurem ent Equipm ent Setup
GND
VIN
Figure 2. M easuring Input or Output Ripple
2
LT3684
3
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