DC992A - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 992
MONOLITHIC SYNCHRONOUS BUCK REGULATOR
LTC3549EDCB
DESCRIPTION
Demonstration circuit 992 is a Step-Down Converter, using the LTC3549 monolithic synchronous
buck regulator. The DC992A has an input voltage
range of 1.6V to 5.5V, and is capable of delivering
up to 250 mA of output current at a minimum input
voltage of 1.8V. The output voltage of the DC992A
can be set as low as 0.611V, the reference voltage
of the LTC3549. At low load currents, the DC992A
can operate in either noise sensitive applications,
due to the capability of the LTC3549 to operate in
pulse-skipping mode, or in high efficiency applications, because the LTC3549 can also operate in
Burst-Mode. Of course, in continuous mode, or
large load current applications, the DC992A is a
high efficiency circuit - over 90%. The DC992A
consumes only 50 uA during sleep mode operation,
and during shutdown, it consumes at less than 1 uA
typically. Because of the high switching frequency
of the LTC3549 - 2.25 MHz - the DC992A uses low
profile surface mount components. These features,
plus the LTC3549 coming in a small 6-Lead DFN
package, make the DC992A an ideal circuit for use
in battery-powered, hand-held applications.
Design files for this circuit board are available.
Call the LTC factory.
LTC is a trademark of Linear Technology Corporation
Table 1.
Performance Summary (TA = 25°C)
PARAMETER
CONDITIONS
VALUE
Minimum Input Voltage
1.6V
Maximum Input Voltage
5.5V
1.2V ±4% (1.152V to 1.248V)
Output Voltage VOUT Regulation
VIN = 1.6V to 5.5V, IOUT = 0A to 250 mA
1.5V ±4% (1.44V to 1.56V)
1.8V ±4% (1.728V to 1.872V)
Typical Output Ripple VOUT
Operation Modes
Nominal Switching Frequency
VIN = 3.6V, IOUT = 250 mA (20 MHz BW)
<20mVP–P
Burst Mode - VIN = 3.6V, VOUT = 1.8V
~40 mA ± 8 mA
Pulse-Skip - VIN = 3.6V, VOUT = 1.8V
~40 mA ± 8 mA
2.25 MHz
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 992
MONOLITHIC SYNCHRONOUS BUCK REGULATOR
QUICK START PROCEDURE
Demonstration circuit 992 is created to evaluate the
performance of the LTC3549. For proper measurement equipment configuration, set up the circuit according to the diagram in Figure 1. Before proceeding
to test, insert jumper JP1 shunt into the off position,
connecting the RUN pin to ground (GND), which
shuts down the circuit. Also insert shunts into the
Pulse-Skip position of jumper JP2, and into the 1.2V
output voltage position.
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 output voltage ripple by touching the probe tip directly
across the Vin or Vout and GND terminals. See
Figure 2 for proper scope probe technique.
3.
Vary the input voltage from 1.6V to 5.5V and adjust
the load current from 0 to 250 mA. Vout should
read between 1.2V +/- 4% (1.152V to 1.248V).
Measure the output ripple voltage at any output
current level above 50 mA; it will measure less
TM
than 20 mVAC. The Burst-Mode and Pulse-Skip
capability of the LTC3549 can also be observed
now by setting the JP2 jumper shunt into either the
Pulse-Skip position or the Burst-ModeTM position,
and decreasing the load current below ~40 mA.
4.
Observe the voltage waveform at the switch node.
Verify the switching frequency is between 1.8 MHz
and 2.7 MHz (T = 0.556 us and 0.37 us), and that
the switch node waveform is rectangular in shape.
NOTE: When
1.
Apply 3.6V at Vin and set the load to 50 mA.
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.
2.
Turn on the circuit by inserting the shunt in jumper
JP1 into the ON position. The output voltage
should be regulating. Measure Vout - it should
measure 1.2V +/- 2% (1.176V to 1.224V).
Insert jumper JP1 shunt into the OFF position and
move the 1.2V Vout shunt into any of the remaining
output voltage options: 1.5V or 1.8V. Just as in the
1.2Vout test, the output voltage should read Vout +/2% tolerance under static line and load conditions,
and another +/- 2% tolerance under dynamic line and
load conditions (+/- 4% total). When finished, turn off
the circuit by inserting the jumper JP1 shunt into the
OFF position.
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 992
MONOLITHIC SYNCHRONOUS BUCK REGULATOR
Figure 1. Proper Measurement Equipment Setup
Figure 2. Measuring Input or Output Ripple
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 992
MONOLITHIC SYNCHRONOUS BUCK REGULATOR
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