DC1212A - Demo Manual

DEMO C IR C U IT 12 12
Q U IC K LT3480/LT3685
S TA R T G U IDE
L T 3 4 8 0 EDD/ L T 3 6 8 5 EDD
2 A , 3 8 V S te p -d o w n S w itc h in g R e g u la to r w ith
S Y N C F u n c tio n a n d EMC filte rs
DESCRIPTION
Demonstration circuit 1212 is a monolithic step-dow n
DC/DC sw itching regulator featuring LT3480/LT3685.
The LT3480 is on DC1212A-A circuit and the LT3685 is
on DC1212A-B circuit. Both the LT3685 and LT3480 can
be synchronized over a 250 KHz to 2 M Hz range. The
demo board is designed for 5V output from a 6.3V to
38V input w ith transient up to 60V. The w ide input range
allow s a variety of input sources. The typical sources are
automotive batteries, w all adaptors and industrial supplies.
The EM C filter at the input makes the circuit compatible
w ith EM C stardard, EN55022 Class B. The current mode
control scheme creates fast transient response and good
loop stability. The RUN/SS pin can be used to set the part
in micropow er shutdow n mode,reducing the supply current to less than 1uA. The RUN/SS pin can also be used
to program soft start. In this mode, the RUN/SS pin is
driven through an external RC filter to create a voltage
ramp on this pin. The soft start function reduces the input current surge during start-up.
The LT3480/LT3685 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 1212.
Note:It is best to ground the SYNC pin ifthe SYNC function 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.
Perform ance Sum m ary for Step-dow n Sw itching R egulator ( TA = 25oC )
PAR AM ETER FO R BU CK R EG ULATO 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
6.3V
38V
5V +/- 4%
2A
800kH z
Q U ICK STA RT PROCEDU RE
Demonstration circuit 1212 is easy to set up to evaluate
the performance ofthe LT3480/LT3685. Refer 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 GND.
3. Turn on the pow er at the input.
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. Once the proper output voltage is established, adjust
the load w ithin the operating range and observe the
1
LT3480/LT3685
output voltage regulation, ripple voltage, efficiency
and other parameters.
6. An external clock can be added to the SYNC pin w hen
SYNC function is used. See synchronization section in
the datasheet for details.
Figure 1. Proper M easurem ent Equipm ent Setup
GND
VIN
Figure 2. M easuring Input or Output R ipple
2
LT3480/LT3685
90dBµV
10dBuV/div
EN55022 Class B Limit
50dBµV
Figure 3. 12V to 5V @ 2A conductive em ission result
EN55022 Class B Limit
Figure 4. 12V to 5V @ 2A radiated em ission result
3
LT3480/LT3685
4
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