QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 662
36V 600MA 500KHZ SOT-23 STEP-DOWN REGULATOR
LT1933
DESCRIPTION
Demonstration circuit 662 is a monolithic step-down
DC/DC switching converter featuring the LT®1933.
The board is optimized for 3.3V output at up to
500mA load current for a steady state input voltage
range of 4.5V to 36V. With its wide input voltage
range, high current internal power switch, low drop-
out operation, 500kHz switching frequency and tiny
SOT-23 package, the LT1933 is a very versatile and
powerful IC for DC/DC converters that require ex-
tremely compact space, high efficiency and high input
voltage.
The LT1933 500kHz switching frequency allows all of
the components to be small, surface mount devices.
The current-mode control topology creates fast tran-
sient response and good loop stability with a mini-
mum number of external components. The low resis-
tance internal power switch (0.37V
V
CE
sat)
achieves
high efficiencies of up to 84%. The shutdown pin can
be used to program undervoltage lockout or place the
part in micropower shutdown, reducing supply cur-
rent to less than 2µA by driving the pin low (
without
R1 installed
). The internal soft start function reduces
input current surge during start-up.
The LT1933 datasheet gives a complete description of
the part, operation and applications information. The
datasheet must be read in conjunction with this Quick
Start Guide for demonstration circuit 662. In particu-
lar, the datasheet section on ‘Thermal Calculations’ is
important for estimating whether a given application’s
combination of input voltage, load current, ambient
temperature and frequency will cause the LT1933 to
exceed it’s absolute maximum rated junction tem-
perature. The LT1933 is assembled in a small low
profile SOT-23 ThinSOT package. Proper board layout
is essential for maximum thermal performance. See
the datasheet section ‘Layout Considerations’.
Design files for this circuit board are available. Call
the LTC factory.
LT is a trademark of Linear Technology Corporation
QUICK START PROCEDURE
Demonstration circuit 662 is easy to set up to evalu-
ate the performance of the LT1933. Refer to Figure 1
for proper measurement equipment setup and follow
the procedure below:
NOTE:
Make
sure that the input voltage does not ex-
higher ESR Aluminum Electrolytic capacitor, C4, is
placed at the input terminals. This may protect
against some, but not all, input transients due to hot-
plugging with a power supply.
See Application Note
88 for more details.
the power supply (with power off),
load, and meters as shown in Figure 1.
1.
NOTE:
Connect
ceed 36V.
NOTE:
The
shutdown function is optional and its ter-
minal can be left floating (disconnected) if shutdown
is not being used.
After all connections are made, turn on input power
and verify that the output voltage is 3.3V.
the output voltage is too low, temporarily
disconnect the load to make sure that the load is
not set too high.
NOTE:
If
not hot-plug the input voltage terminal VIN.
The absolute maximum voltage on VIN is 36V and
hot-plugging a power supply through wire leads to
the demonstration circuit can cause the voltage on
the extremely low-ESR ceramic input capacitor to ring
to twice its DC value. In order to protect the IC, a
NOTE:
Do
2.
Once the proper output voltages are established,
adjust the load within the operating range and ob-
1
PCB设计
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