DEMO CIRCUIT 1091
LT3480
QUICK START GUIDE
LT3480EMSE
2A, 38V Step-Down Switching Regulator with
SYNC Function
DESCRIPTION
Demonstration circuit 1091 is a monolithic step-dow n
DC/ sw itching regulator f
DC
eaturing the LT3480. The
operating f
requency can be synchronized up to 2 M H z.
The demo board is designed f 5V output f
or
rom a 6.3V to
38V input w ith transients up to 60V. The w ide input range
of the LT3480 allow s a variety of input sources. The typi-
cal sources are automotive batteries, w all adaptors and
industrial supplies. The modes of operation (Burst M ode
and f
ixed f
requency) are j
umper selectable. The Burst
M ode operation increases the ef iciency at light loads
f
ixed f
requency mode maintains a constant sw itch-
w hile f
ing f
requency regardless ofthe load current.
The current mode control scheme creates f transient
ast
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 LT3480’
s
Perform ance Sum m ary for Step-Dow n Sw i ng Regul
tchi
ator (TA = 25oC )
PAR AM ETER FO R BU CK R EG U LATO R
M inimum I
nput Voltage
M aximum I
nput Voltage
O utput Voltage V
OUT
M aximum O utput Current
Typical Sw itching Frequency
CO N DI O N
TI
VALU E
6.3V
38V
5V
+/- 4%
2A
550kH z
integrated boost diode reduces the parts count. The
R U N / pin can be used to set the part in micropow er
SS
shutdow n mode,reducing the supply current to less than
1uA. The R U N / pin can also be used to program sof
SS
t
start. I this mode, the R U N / pin is driven through an
n
SS
external R C f to create a voltage ramp. The sof start
ilter
t
f
unction reduces the input current surge during start-up.
The LT3480 datasheet gives a complete description of
the part,operation and application inf
ormation. The data-
sheet must be read in conj
unction w ith this quick start
guide f demo circuit 1091.
or
Design files for this circuit board are available. Call
the LTC factory.
,LTC and LT are registered trademarks ofLinear Technology Corporation.
QUICK START PROCEDURE
Demonstration circuit 1091 is easy to set up to evaluate
the perf
ormance of the LT3480. R ef to Figure 1 f
er
or
proper measurement equipment setup and f
ollow 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 f proper scope probe
or
technique.
2.
3.
4.
W ith pow er of ,connect the input pow er supply to Vin
f
and G N D.
Turn on the pow er at the input.
Check f the proper output voltage.
or
NOTE.
I there is no output,temporarily disconnect the load to make
f
sure that the load is not set too high.
5.
1.
Place JP1 on the R U N position.
O nce the proper output voltage is established, adj
ust
the load w ithin the operating range and observe the
1
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