DC1023A
LT3505
QUICK START GUIDE
LT3505
1.2A, Step-down Switching Regulator in
3mm×3mm DFN
DESCRIPTION
Demo ci t DC1023A i a monoli c step-dow n DC/
rcui
s
thi
DC
sw i ng regulator f
tchi
eaturi the LT3505. The demo ci
ng
r-
cui i desi
t s
gned f 5V output f
or
rom a 6V to 36V i
nput.
The w i i
de nput range of the LT3505 allow s a vari of
ety
i
nput sources. The typi sources are automoti batter-
cal
ve
i w all adaptors and i
es,
ndustri suppli The osci
al
es.
llator
can be programmed f hi f
or gh requency operati allow -
on
i the use of ti low cost external components or i
ng
ny,
t
can be programmed f low er f
or
requency operati to
on
maxi ze ef i ency. The current mode control scheme
mi
fci
ast
ent
li
creates f transi response and good loop stabi ty.
The gate dri of the i
ve
nternal sw i i boosted to a volt-
tch s
age that i hi
s gher than Vi to ensure saturati of the
n
on
sw i A charge pump consi ng of a di and capaci
tch.
sti
ode
-
orms the boost f
uncti The
on.
tor on the demo board perf
SH DN pi can be used to set the part i shutdow n mode,
n
n
reduci the supply current to less than 2uA. The SH DN
ng
pi can also be used to program sof start. I thi mode,
n
t
n s
the SH DN pi i dri through an external R C flter to
n s ven
i
create a voltage ramp on thi pi The sof start f
s n.
t
uncti
on
reduces the i
nput current surge duri start-up. Cycle by
ng
cycle current li t, f
mi requency f
oldback and thermal shut-
dow n provi the protecti agai shorted outputs.
de
on
nst
The LT3505 datasheet gi a complete descri on of
ves
pti
the part,operati and appli on i ormati The data-
on
cati nf
on.
sheet must be read i conjuncti w i thi qui start
n
on th s ck
gui f demo ci t DC1023A.
de or
rcui
Design files for this circuit board are available. Call
the LTC factory.
,LTC and LT are regi
stered trademarks ofLi
near Technology Corporati
on.
Performance Summary ( TA = 25oC )
PAR AM ETER
Mi mum I
ni
nput Voltage
Maxi
mum I
nput Voltage
O utput Voltage V
OUT
Sw i ng Frequency
tchi
Sw i ng Frequency
tchi
Maxi
mum O utput Current
Ef i ency
fci
Ef i ency
fci
Voltage R i
pple
Voltage R i
pple
CO N DI O N
TI
VALU E
6V
36V
5.05V
±4%
2.2MH z
±10%
750kH z
±10%
1.0A
85.0%
83.3%
5mV
20mV
JP2 i 2.2MH z posi on
n
ti
JP2 i 750kH z posi on
n
ti
V
IN
=8~32V
V
IN
=12V,I =1A,Freq=750kH z
out
V
IN
=12V,I =1A,Freq=2.2MH z
out
V
IN
=12V,I =1A,Freq=2.2MH z
out
V
IN
=12V,I =1A,Freq=750kH z
out
1
LT3505
QUICK START PROCEDURE
Demonstrati ci t 1023 i easy to set up to evaluate
on rcui
s
the perf
ormance of the LT3505. R ef to Fi
er
gure 1 f
or
proper measurement equi
pment setup and f
ollow the
procedure below :
NOTE.
W hen measuri the i
ng
nput or output voltage ri
pple,care must be
taken to avoi a long ground lead on the osci
d
lloscope probe. Measure the
i
nput or output voltage ri by touchi the probe ti di
pple
ng
p rectly across the
Vi or Vout and GND termi
n
nals. See Fi
gure 2 f proper scope probe
or
techni
que.
3.
4.
W i pow er of ,connect the i
th
f
nput pow er supply to Vi
n
and G N D.
Turn on the pow er at the i
nput.
NOTE.
Make sure that the i
nput voltage does not exceed 36V.
5.
Check f the proper output voltages.
or
NOTE.
I there i no output,temporari di
f
s
ly sconnect the load to make
sure that the load i not set too hi
s
gh.
1.
2.
Place JP1 on the R U N posi on.
ti
Place JP2 on the selected f
requency
6.
O nce the proper output voltage i establi
s
shed, adjust
the load w i n the operati range and observe the
thi
ng
output voltage regulati ri
on, pple voltage,ef i ency and
fci
other parameters.
Figure 1. Proper M easurem ent Equipm ent Setup
Figure 2. M easuring I
nput or Output Ripple
VIN
GND
2
LT3505
INPUT VOLTAGE
FREQUENCY FOLDBACK
W hen FR EQ jumper (JP2) i selected as 2.2M, the
s
sw i ng f
tchi requency i 2.2MH z w i n 6V to 16V i
s
thi
nput
voltage range. The sw i ng f
tchi requency w i be li
ll
nearly
decreased w hen the i
nput voltage i
ncreases. The i
nput
voltage f
requency f
oldback curve i show n i Fi
s
n gure 3.
2.5
2
Freq (MHz)
W hen the FR EQ jumper (JP2) i selected as 750K, the
s
sw i ng f
tchi requency i fxed at 750kH z w i n 6V to
s i
thi
36V i
nput voltage range.
1.5
1
0.5
0
0
10
Vin (V)
20
30
40
Figure 3. I
nput Voltage Frequency Foldback
OUTPUT CAPABILITY
V
O U T
=5V
Vi (V)
n
6
8
32
36
I max (A)
o
750K
2.2M
0.7
0.05
1
1
1
1
1
0.4
3
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