DC1445A - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1445A
HIGH INPUT VOLTAGE 2.5A MONOLITHIC SYNCHRONOUS BUCK REGULATOR
LTC3603EMSE
DESCRIPTION
Demonstration circuit 1445A is a step-down converter, using the LTC3603EMSE monolithic synchronous buck regulator. The DC1445A has an input voltage range of 4.5V to 15V, and is capable of
delivering up to 2.5A of output current. The output
voltage of the DC1445A can be set as low as 0.6V,
the reference voltage of the LTC3603EMSE. At low
load currents, the DC1445A can operate in either
noise sensitive applications, due to the capability of
the LTC3603EMSE to operate in pulse-skipping
mode, or in high efficiency applications, because
the LTC3603EMSE can also operate in BurstMode®. Of course, in continuous mode, or large
load current applications, the DC1445A is a high
efficiency circuit - over 90%. The DC1445A con-
sumes less than 1 mA of quiescent current during
sleep operation typically, and during shutdown, it
consumes less than 50 uA. Because of the high
switching frequency of the LTC3603EMSE, which
is programmable up to 3 MHz, the DC1445A uses
low profile surface mount components. These features, plus the LTC3603EMSE coming in a 16-Lead
MSOP package, make the DC1445A an ideal circuit
for use in high voltage portable, battery-powered
applications.
Design files for this circuit 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
4.5V
Maximum Input Voltage
15V
GND = Shutdown
Run/Shutdown
VIN = Run
2.5V ±4% (2.4V – 2.6V)
Output Voltage VOUT Regulation
VIN = 4.5V to 15V, IOUT = 0A to 2.5A
3.3V ±4% (3.168V – 3.432V)
5V ±4% (4.8V – 5.2V)
Typical Output Ripple VOUT
Operation Modes
Nominal Switching Frequency
VIN = 12V, VOUT = 5V, IOUT = 2.5A (20 MHz BW)
< 30mVP–P
Burst Mode - VIN = 12V, VOUT = 3.3V
< 1.5 A
Pulse-Skip - VIN = 12V, VOUT = 3.3V
< 650 mA
RT = 105k
1 MHz
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1445A
HIGH INPUT VOLTAGE 2.5A MONOLITHIC SYNCHRONOUS BUCK REGULATOR
QUICK START PROCEDURE
Demonstration Circuit 1445A is easy to set up to
evaluate the performance of the LTC3603EMSE. For
proper measurement equipment configuration, set up
the circuit according to the diagram in Figure 1. Before proceeding to test, insert shunts into the OFF
position of header JP5, which connects the RUN pin
to ground (GND), and thus, shuts down the circuit,
the forced continuous (FC) position of header JP6,
the external soft-start (EXT SS) position of header
JP7, and the 3.3V output voltage header, JP2.
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 output voltage ripple by touching the probe tip directly across
the Vin or Vout and GND terminals. See Figure 2 for
proper scope probe measurement technique.
With the DC1445A set up according to the proper
measurement and equipment in Figure 1, apply 6.3V
at Vin (Do not hot-plug Vin or increase Vin over the
rated maximum supply voltage of 15V, or the part
may be damaged.). Measure Vout; it should read 0V.
Turn on the circuit by inserting the shunt in header
JP5 into the ON position. The output voltage should
be regulating. Measure Vout - it should measure
3.3V +/- 2% (3.234V to 3.366V).
Vary the input voltage from 4.5V to 15V and adjust
the load current from 0 to 2.5A. Vout should read
3.3V +/- 4% (3.168V to 3.432V).
Adjust the output current to 2A. Measure the output
ripple voltage; it will measure less than 20 mVAC.
Observe the voltage waveform at the switch node
(pins 16 thru 19). Verify the switching frequency is
between 800 kHz and 1.2 MHz (T = 1.25 us and 0.833
us), and that the switch node waveform is rectangular
in shape.
Change the JP6 shunt from forced continuous mode
to Burst Mode®. Also set the input voltage to 12V
and the output current to any current less than 1.5A.
Observe the Burst Mode® operation at the switch
node, and measure the output ripple voltage. It
should measure less than 200 mV. For lower output
ripple voltage, set the mode to pulse-skip and adjust
the output current to any current less than 650 mA.
Observe the pulse-skip mode of operation at the
switch node. Also, measure the output ripple voltage;
it should measure less than 40 mV.
Insert the JP5 shunt into the OFF position and move
the shunt in 3.3V Vout JP2 header into any of the two
remaining output voltage option headers: 2.5V or 5V.
Just as in the 3.3V Vout test, the output voltage
should read Vout +/- 2% tolerance under static line
and load conditions, and +/- 1% tolerance under dynamic line and load conditions (+/- 2% total). Also,
the circuit operation in either Burst Mode® or pulseskip will be the same.
When finished, turn off the circuit by inserting the
shunt in header JP5 into the OFF position (connecting
the RUN pin to ground).
Low Output Voltage Configuration
For applications with output voltages less than 2V, the
inductor value of 3.3 uH on the DC1445A should be
changed to 1.5 uH. This is required so that the inductor ripple current “ramp” waveform has a large
enough slope for the current comparator (to distinguish
it
from
noise
voltages).
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1445A
HIGH INPUT VOLTAGE 2.5A MONOLITHIC SYNCHRONOUS BUCK REGULATOR
Figure 1. Proper Equipment Measurement Set-Up
Figure 2. Measuring Input or Output Ripple
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1445A
HIGH INPUT VOLTAGE 2.5A MONOLITHIC SYNCHRONOUS BUCK REGULATOR
Normal Switching Frequency & Output Ripple Voltage
Waveforms
Figure 3. Switch Waveform & Output Ripple Voltage
V = 12V, V = 3.3V, I = 2.5A, Fsw = 1 MHz
IN
OUT
OUT
Trace 1: Switch Voltage (5 V/div)
Trace 3: Output Ripple Voltage (20 mV/div AC)
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1445A
HIGH INPUT VOLTAGE 2.5A MONOLITHIC SYNCHRONOUS BUCK REGULATOR
Load Step Response Waveform
Figure 4. Load Step Response
V = 12V, V = 3.3V, 2A Load Step (500 mA <-> 2.5A)
IN
OUT
Forced Continuous Mode Fsw = 1 MHz
Trace 3: Output Voltage (100mV/div AC)
Trace 4: Output Current (1A/div)
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1445A
HIGH INPUT VOLTAGE 2.5A MONOLITHIC SYNCHRONOUS BUCK REGULATOR
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