QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 702
HIGH EFFICIENCY, THINSOT™ SYNCHRONOUS BUCK REGULATOR
1
LTC3406B-2ES5
DESCRIPTION
Demonstration circuit DC702 is a 2.25 MHz step-
down converter, using the LTC3406B monolithic syn-
chronous buck regulator. The DC702 has an input
voltage range of 2.5V to 5.5V, and is capable of deliv-
ering up to 600 mA of output current at a minimum
input voltage of 3V. The DC702 is made for noise
sensitive applications, due to the LTC3406B-2 oper-
ating in pulse-skipping mode at low load currents.
The DC702 is a high efficiency circuit - up to 90%,
and during shutdown, the DC702 consumes less than
1 uA. These features, plus the LTC3406B coming in a
tiny 5-Pin ThinSOT package and having an operating
frequency of 2.25 MHz (allowing the exclusive use of
low profile surface mount components), make the
DC702 an ideal circuit for use in battery-powered,
hand-held applications.
Design files for this circuit board are available. Call
the LTC factory.
Burst Mode and ThinSOT are trademarks of Linear Technology Corporation
Table 1.
Performance Summary (TA = 25°C)
PARAMETER CONDITION VALUE
Minimum Input Voltage 2.5V
Maximum Input Voltage 5.5V
Output Voltage VOUT VIN = 2.5V to 5.5V, IOUT = 0A to 600 mA 1.8V ±2%
Typical Output Ripple VOUT VIN = 5V, IOUT = 600 mA (20 MHz BW) 20mVP–P
Line ±1%
Output Regulation Load ±1%
Nominal Switching Frequency 2.25 MHz
QUICK START PROCEDURE
The DC702 demonstration circuit is easy to set up to
evaluate the performance of the LTC3406B-2. One
word of caution: when the board is right-side up (the
title is legible at the top of the board), the output volt-
age turret is on the left side of the board, and the in-
put voltage turret is on the right side of the board.
Set up the circuit appropriately. Before proceeding to
test, insert jumper JP1 into the upper position, con-
necting the RUN pin to ground (GND), which shuts
down the circuit. Refer to Figure 1 for proper meas-
urement equipment setup and follow the procedure
below:
NOTE:
When measuring the input or output voltage
ripple, care must be taken to avoid a long ground lead
on the oscilloscope probe. Measure the input or out-
put voltage ripple by touching the probe tip directly
across the Vin or Vout and GND terminals. See Fig-
ure 2 for proper scope probe technique.
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 702
HIGH EFFICIENCY, THINSOT™ SYNCHRONOUS BUCK REGULATOR
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1.
Connect the input power supply to the Vin and
GND terminals on the right-side of the board. Do
not hot-plug Vin or increase Vin over the rated
maximum supply voltage of 5.5V, or the part may
be damaged.
2.
Connect the load between the Vout and GND ter-
minals on the left-side of the board.
3.
Apply 3.3V at Vin. Measure Vout; it should read
0V. If desired, one can measure the shutdown
supply current at this point. The supply current
will be approximately 1 uA in shutdown.
4.
Turn on the circuit by connecting the RUN pin to
Vin or inserting the JP1 jumper into the ON (lower)
position. Measure Vout - it will measure approxi-
mately 1.8V.
5.
Vary the input voltage from 2.5V to 5.5V and adjust
the load current from 0 to 600mA. The output volt-
age should be regulating. Measure the output rip-
ple voltage at any output current level; it should
measure less than 20 mVAC.
6.
Observe the voltage waveform at the switch node
(pin 3). Verify the switching frequency is between
1.8 MHz and 2.7 MHz (T = 0.555 us and 0.370 us),
and that the switch node waveform is rectangular
in shape.
When finished, turn off the circuit (connecting the
RUN pin to ground) by inserting the JP1 jumper into
the OFF (upper) position.
Warning - if long leads are used to power the demo circuit, the input voltage at the part could “ring”. To elimi-
nate this, insert a small tantalum capacitor (for instance, an AVX part # TAJW226M010R) on the pads between
the input power and return terminals on the bottom of the demo board. The (greater) ESR of the tantalum will
dampen the (possible) ringing voltage due to the use of long input leads. On a normal, typical PCB, with short
traces, the capacitor is not needed.
If more efficiency is desired from the demo circuit, replace the stock inductor, a Taiyo Yuden part #
LQLBC2518M2R2M, with a Murata inductor, # LQH32CN2R2M11. Due to its larger size, the Murata inductor
has lower DCR than the Taiyo Yuden inductor, thus has less power dissipation.
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 702
HIGH EFFICIENCY, THINSOT™ SYNCHRONOUS BUCK REGULATOR
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Figure 1. Proper Measurement Equipment Setup
Figure 2. Measuring Input or Output Ripple
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 702
HIGH EFFICIENCY, THINSOT™ SYNCHRONOUS BUCK REGULATOR
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