QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 474
4A, 500KHZ STEP DOWN SWITCHING REGULATOR
LT1374CFE
DESCRIPTION
Demonstration circuit 474 is a step-
down buck regulator using the
LT1374CFE 500kHz-switching regulator.
The high switching frequency allows
the use of small inductors and filter
components, making this circuit ideal
for space conscious systems.
0.8
0.85
0.9
0.95
0
1
2
3
4
5
Load Current
Ef
fi
ci
en
cy
Figure 1.
Efficiency, 10V V
IN
, 5V V
OUT
Figure 1 shows efficiency versus load
for a typical application. The best
efficiency is realized with a load
current between 700mA and 2 amps.
Full load efficiency is 87%. The
maximum allowed die temperature is
125°C. Figure 2 shows die temperature
vs. output load current with V
IN
of
12V. At full load the die temperature
rise is 70°C indicating that the demo
is suitable for ambient temperatures
of up to 125°C – 70°C = 55°C.
0
20
40
60
80
0
1
2
3
Load (Amps)
Te
m
p
er
at
ur
e
(De
g
ree
s
C)
4
Figure 2.
Die Temperature vs Output
Current, V
IN
= 12V
QUICK START PROCEDURE
Refer to Figure 3 for proper measure-
ment equipment setup and follow the
procedure below:
1.
Connect input power to the Vin and
GND terminals. V
IN
should be be-
tween 5V and 25V. The power source
should be capable of delivering
25W.
NOTE:
5V output operation requires
a minimum V
IN
of 6V
2.
Connect the output load to the Vout
and GND terminals.
3.
Select desired output voltage using
the voltage selecting jumper
NOTE:
Choose 3.3V operation by mov-
ing the voltage selection jumper to
the 3.3V position. Demonstration
circuit 474 is optimized for 5V op-
eration, and when operating at 3.3V
out, high V
IN
and light load some
instability may arise. Increasing
the output capacitance removes this
instability. Use a 330µF, 4V, low
ESR cap such as the “Poscap” or
“Oscon”.
1
