DEMO CIRCUIT 1167
LT3685
QUICK START GUIDE
LT3685EMSE
2A, 38V Step-down Switching Regulator
with SYNC Function
DESCRIPTION
Demonstration circuit 1167 is a monolithic step-dow n
DC/ sw itching regulator f
DC
eaturing LT3685. The LT3685
can be synchronized over a 250 KH z to 2 M H z range. The
demo board is designed f 5V output f
or
rom a 6.3V to
38V input w ith transient up to 60V. The w ide input range
of the LT3685 allow s a variety of input sources. The typi-
cal sources are automotive batteries, w all adaptors and
industrial supplies.
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 LT3685’
s
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
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
start. I this mode, the R U N / pin is driven through an
n
SS
external R C f to create a voltage ramp on this pin. The
ilter
sof start f
t
unction reduces the input current surge during
start-up.
The LT3685 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 1167.
or
N ote:I is best to ground the SYN C pin if the SYN C f
t
unc-
tion is not being used.
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.
QUICK START PROCEDURE
Demonstration circuit 1167 is easy to set up to evaluate
the perf
ormance of the LT3685. 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
RF/Wirelessly
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