40V MICROPOWER DFN BUCK REGULATOR WITH INTEGRATED BOOST AND CATCH
DIODES
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1037
LT3470
DESCRIPTION
Demonstration circuit 1037 is a 40V micropower DFN
buck regulator featuring the LT®3470. The board is
optimized for 5V output at up to 200mA load current
for a steady state input voltage range of 5.5V to 40V.
With its wide input voltage range, high efficiency in-
ternal power switch, low dropout operation, hyster-
etic current-mode, integrated boost and catch diodes
and tiny SOT-23 package, the LT3470 is a very versa-
tile and powerful IC for DC/DC converters that require
extremely compact space, high efficiency and high
input voltage.
The LT3470 hysteretic control scheme allows all of
the components to be small, surface mount devices
while providing minimum output ripple voltage at all
load currents. The current-mode control topology
creates fast transient response and good loop stabil-
ity with a minimum number of external components.
The low resistance internal power switch achieves
high efficiencies of up to 82% at 12V input. The shut-
down jumper can be used to place the part in micro-
power shutdown, reducing supply current to less
than 1µA by driving the pin low. The internal boost
and catch diodes simplify layout and reduce compo-
nent count, providing the smallest solution possible.
The LT3470 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 1037. In par-
ticular, the datasheet section on ‘Thermal Calcula-
tions’ is important for estimating whether a given ap-
plication’s combination of input voltage, load current,
ambient temperature and frequency will cause the
LT3470 to exceed it’s absolute maximum rated junc-
tion temperature. The LT3470EDDB is assembled in a
small low profile DFN 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 1037 is easy to set up to evalu-
ate the performance of the LT3470. Refer to Figure 1
for proper measurement equipment setup and follow
the procedure below:
NOTE:
Make sure that the input voltage does not ex-
ceed 40V.
NOTE:
The shutdown jumper shunt is required to be
the extremely low-ESR ceramic input capacitor to ring
to twice its DC value. In order to protect the IC, a
higher ESR Aluminum Electrolytic capacitor 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 de-
tails.
NOTE:
Connect the power supply (with power off),
placed in the shutdown position or the VOUT ENABLE
position for proper operation.
NOTE:
Do not hot-plug the input voltage terminal VIN.
load, and meters as shown in Figure 1.
1.
After all connections are made, turn on input power
The absolute maximum voltage on VIN is 40V and
hot-plugging a power supply through wire leads to
the demonstration circuit can cause the voltage on
and verify that the output voltage is 5V.
1
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