DEMO CIRCUIT 964A
LT3501
QUICK START GUIDE
LT3501
3A Dual Monolithic
Step-Down DC/DC Converter
DESCRIPTION
Demo circuit 964A is a dual monolithic step-dow n DC/
DC
converter f
eaturing LT3501. The demo circuit is designed
f 3.3V and 1.8V outputs f
or
rom a 4.5V to 24V input. The
current capability of each channel is up to 3A. Independ-
ent input voltage, f
eedback, sof
t-start and pow er good
pins f each channel simplif complex pow er supply
or
y
tracking/
sequencing requirements.
Both converters are synchronized to either a common
external clock input or a resistor programmable 250kH z
to 1.5M H z internal oscillator. At all f
requencies, a 180°
t
phase shif betw een channels is maintained, reducing
voltage ripple and component size. Programmable f
re-
quency allow s f optimization betw een ef iciency and
or
f
external component size.
M inimum input-to-output voltage ratios are improved by
allow ing the sw itch to stay on through multiple clock cy-
cles, only sw itching of w hen the boost capacitor needs
f
recharging,resulting in ~95% maximum duty cycle.
Each output can be independently disabled using its ow n
sof
t-start pin, or by using the SH DN pin the entire part
can be placed in a low quiescent current shutdow n
mode.
The LT3501 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 964A.
or
Design files for this circuit board are available. Call
the LTC factory.
,LTC and LT are registered trademarks ofLinear Technology Corporation.
Performance Summary ( TA = 25oC )
PAR AM ETER
M inimum Input Voltage
M aximum Input Voltage
O utput Voltage V
OUT1
O utput Voltage V
OUT2
Sw itching Frequency
M aximum O utput Current Iout1 and Iout2
Voltage R ipple V
OUT1
Voltage R ipple V
OUT2
CO N DI O N
TI
VALU E
4.5V
24V
3.3V
±4%
1.8V
±4%
500kH z
±20%
3.0A
2.8A
<10mV
<10mV
V
IN
=4.5~16V
V
IN
=16~24V
V
IN
=12V,Iout1=3A
V
IN
=12V,Iout2=3A
1
LT3501
QUICK START PROCEDURE
Demo circuit 964A is easy to set up to evaluate the per-
f
ormance of the LT3501. R ef to Figure 1 f proper
er
or
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
V
IN
or V
O U T
and GND terminals. See Figure 2 f proper scope probe
or
technique.
3.
Turn on the pow er at the input.
NOTE.
M ake sure that the input voltage does not exceed 24V.
4.
Check f the proper output voltages.
or
NOTE.
Ifthere is no output,temporarily disconnect the load to make
sure that the load is not set too high.
5.
1.
2.
Place JP1 on the CO M BINED position.
W ith pow er of , connect the input pow er supply to
f
V
IN1
and G ND. (Connect another input pow er supply
to V
IN2
and G ND ifINDEPENDENT is selected.)
O nce the proper output voltage is established, adj
ust
the load w ithin the operating range and observe the
output voltage regulation,ripple voltage,ef iciency and
f
other parameters.
Figure 1. Proper M easurem ent Equipm ent Setup
2
LT3501
Figure 2. M easuring I
nput or Output Ripple
VIN
GND
ADDITIONAL NOTES
1. Install a 10k resistor at R 22 if the board is synchro-
nized f
rom an external signal generator.
2. Dif erent tracking and sequencing schemes can be
f
exercised. H ow ever, the Vout1 should stay on f
or
proper operation ofVout2.
3
Programming Basics
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