DC1072B - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1072B
1A MONOLITHIC SYNCHRONOUS BUCK REGULATOR
LTC3561A
DESCRIPTION
Demonstration circuit 1072B is a step-down converter, using the LTC3561A monolithic synchronous buck regulator. The DC1072B has an input
voltage range of 2.5V to 5.5V, and is capable of
delivering up to 1A of output current. The output
voltage of the DC1072B can be set as low as
0.8V, the reference voltage of the LTC3561A, and
can go as high as 5V. At light load currents, the
DC1072B operates in pulse-skipping mode - ideal
for noise sensitive applications. Of course, in
large load current applications, the DC1072B operates in continuous mode, providing high efficiency - over 95%. The DC1072B consumes less
than 60 uA of quiescent current during sleep operation, and during shutdown, it consumes less
than 1 uA. The DC1072B has a standard operating frequency of 1 MHz, but can be adjusted to
frequencies as high as 4 MHz. Because of the
high switching frequency of the DC1072B, small,
low profile surface mount components are used in
the circuit. These features, plus the LTC3561A
coming in a small 8-Lead DFN package, make the
DC1072B a perfect match for battery-powered,
hand-held applications.
Design files for this circuit board are available. Call the LTC factory.
TM - Burst Mode is a trademark of Linear Technology Corporation
Table 1.
Performance Summary (TA = 25°C)
PARAMETER
CONDITIONS
VALUE
Minimum Input Voltage
2.5V
Maximum Input Voltage
5.5V
1.2V ±4% (1.152V to
1.248V)
Output Voltage VOUT Regulation
VIN = 2.5V to 5.5V, IOUT = 0A to 1A
1.5V ±4% (1.44V to 1.56V)
1.8V ±4% (1.728V to
1.872V)
Typical Output Ripple VOUT
VIN = 5V, IOUT = 1A (20 MHz BW)
<20mVP–P
Operation Mode
Pulse-Skipping - VIN = 3.3V, VOUT = 1.8V
<100mA ±0.1A%
Nominal Switching Frequency
1 MHz
QUICK START PROCEDURE
Demonstration Circuit 1072B is easy to set up
to evaluate the performance of the LTC3561A.
For proper measurement equipment configuration, set up the circuit according to the diagram
in Figure 1. Before proceeding to test, insert
shunts into JP1 OFF position, which connects
the RUN pin to ground (GND), and thus, shuts
down the circuit, and the 1.2V position of JP2.
NOTE: When
measuring the input or output voltage ripple, care must be taken to avoid a long
1
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1072B
1A MONOLITHIC SYNCHRONOUS BUCK REGULATOR
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.
1.
2.
3.
With the DC1072B set up according to the
proper measurement and equipment in Figure 1, apply 3.3V at Vin (Do not hot-plug Vin
or increase Vin over the rated maximum supply voltage of 5.5V, or the part may be damaged.). Measure Vout; it should read 0V. If
desired, one can measure the shutdown supply current at this point. The supply current
will be approximately 10 uA, or less, in shutdown.
Turn on the circuit by inserting the shunt in
header JP1 into the ON position. The output
voltage should be regulating. Measure Vout it should measure 1.2V +/- 2% (1.176V to
1.224V).
Vary the input voltage from 2.5V to 5.5V and
adjust the load current from 0 to 1A. Vout
should read between 1.2V +/- 4% (1.152V to
1.248V).
4.
Measure the output ripple voltage at any output current level; it usually will measure less
than 20 mVAC.
5.
Observe the voltage waveform at the switch
node. Verify the switching frequency is between 850 kHz and 1.15 MHz (T = 1.176 us
and 0.87 us), and that the switch node waveform is rectangular in shape.
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 +/- 1% tolerance under dynamic
line and load conditions (+/- 2% total).
When finished, turn off the circuit (connecting
the RUN pin to ground) by inserting the shunt in
header JP1 into the OFF (upper) position.
Connection Diagram
2
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1072B
1A MONOLITHIC SYNCHRONOUS BUCK REGULATOR
Figure 1. Proper Measurement Equipment Setup
Figure 2. Measuring Input or Output Ripple
3
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1072B
1A MONOLITHIC SYNCHRONOUS BUCK REGULATOR
Figure 3. Switching Operation
VIN = 3.3V, VOUT = 1.5V, 1A Output Current
Trace 1: Switch Voltage (2V/div)
Trace 3: Output Voltage (20mV/div AC)
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1072B
1A MONOLITHIC SYNCHRONOUS BUCK REGULATOR
Figure 4. Load Step Response
VIN = 3.3V, VOUT = 1.5V, 900mA Load Step (0.1A <-> 1A)
Trace 3: Output Voltage (100mV/div AC)
Trace 4: Output Current (500 mA/div)
5
GND
E2
2.65V-5.5V
Cin3
22uF
16V
+
*
Cin2
1uF
OPT
Cin1
10uF
6.3V
Rs1
1M
0
2
SD/RT
SVIN
1
JP1
Rset
549K, 1%
1
6
OFF ON
3
Cbyp
OPT
Rfilt
PVIN
SG ND
2
Rc
8
7
Cc
16.2K
ITH
VFB
SW
3
1000pF
PG ND
4
5
JP2
C1
OPT
8
7
SELECT
USER
Rfb5
OPT
1
2
VIN
1.8V
Rfb4
200K, 1%
6.3V
2.2uH
D1
Cout1
OPT 22uF
L1
6
5
E1
4
3
VIN
1.5V
Rfb3
287K, 1%
Cffw
10pF
2
1
U1
LTC3561AEDD
1.2V
Rfb2
499K, 1%
Rfb1
249K, 1%
Cout2
0.1uF
+
VOUT
E5
GND
E4
GND
1.8V/1.5V/1.2V
Cout3 1.0A
OPT
E3
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1072B
1A MONOLITHIC SYNCHRONOUS BUCK REGULATOR
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