DC716B - Demo Manual

DEMONSTRATION CIRCUIT 716B
QUICK START GUIDE
LT3470
40V MICROPOWER SOT-23 BUCK REGULATOR WITH
INTEGRATED BOOST AND CATCH DIODES
DESCRIPTION
Demonstration circuit 716 is a 40V micropower SOT23 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 7V to
40V. With its wide input voltage range, high efficiency
internal power switch, low dropout operation, hysteretic current-mode, integrated boost and catch diodes
and tiny SOT-23 package, the LT3470 is a very versatile 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 stability with a minimum number of external components.
The low resistance internal power switch achieves
high efficiencies of up to 82% at 12V input. The shutdown jumper can be used to place the part in micropower shutdown, reducing supply current to less
than 1µA by driving the pin low. The internal boost
and catch diodes simplify layout and reduce component 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 716. In particular, 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 LT3470 to
exceed it’s absolute maximum rated junction temperature. The LT3470 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 Corporatio
QUICK START PROCEDURE
Demonstration circuit 716 is easy to set up to
evaluate 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
placed in the shutdown position or the VOUT
ENABLE position for proper operation.
NOTE: Do
not hot-plug the input voltage terminal
VIN. 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 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 details.
1
DEMONSTRATION CIRCUIT 716B
QUICK START GUIDE
NOTE: Connect
the power supply (with power off),
load, and meters as shown in Figure 1.
1.
After all connections are made, turn on input
power and verify that the output voltage is 5V.
2.
Once the proper output voltages are established,
adjust the load within the operating range and
observe the output voltage regulation, ripple
voltage, efficiency and other parameters.
NOTE: If
the output voltage is too low, temporarily
disconnect the load to make sure that the load is
not set too high.
Figure 1. Proper Measurment Equipment Setup
2
E2
E1
GND
+
VIN
7V TO 40V
50V
C1
10uF
1
2
JP1
SHUTDOWN
3
VOUT ENABLE
X7R
50V
1206
C2
1uF
R1
OPT
0402
N/C
VIN
U1
LT3470ETS8
2
3
1
SH D N
4
GN D
6
FB
BIAS
VSW
BOOST
0.22uF
8
7
5
R3
200k
1%
0402
C6
22pF
NPO
0402
X5R 0402
C3
0402
R2 604k 1%
TOKO D52LC
L1 33uH
1206
6.3V
C4
22uF
X5R
0603
C5
OPT
E9
[email protected]
VOUT
DEMONSTRATION CIRCUIT 716B
QUICK START GUIDE
3
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