DC1025A - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1025
800MA MONOLITHIC SYNCHRONOUS BUCK REGULATOR
LTC3560
DESCRIPTION
Demonstration circuit 1025 is a step-down converter,
using the LTC3560 monolithic synchronous buck
regulator. The DC1025 has an input voltage range of
2.5V to 5.5V, and is capable of delivering up to 800
mA of output current. The output voltage of the
DC1025 can be set as low as 0.6V, the reference voltage of the LTC3560. At low load currents, the
DC1025 can operate in either noise sensitive applications, due to the capability of the LTC3560 to operate
in pulse-skipping mode, or in high efficiency applications, because the LTC3560 can also operate in BurstMode. Of course, in continuous mode, or large load
current applications, the DC1025 is a high efficiency
circuit - over 95% in some cases. The DC1025 consumes less than 30 uA of quiescent current during
sleep operation, and during shutdown, it consumes
less than 1 uA. Because of the high switching frequency of the LTC3560 - 2.25 MHz - the DC1025 uses
low profile surface mount components. These features, plus the LTC3560 coming in a small 6-Lead
ThinSot package, make the DC1025 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
2.5V
Maximum Input Voltage
5.5V
GND = Shutdown
Run/Shutdown
VIN = Run
1.2V ±4% (1.152V – 1.248V)
Output Voltage VOUT
VIN = 2.5V to 5.5V, IOUT = 0A to 800 mA
1.5V ±4% (1.44V - 1.56V)
1.8V ±4% (1.728V – 1.872V)
Typical Output Ripple VOUT
Operation Modes
Nominal Switching Frequency
VIN = 3.3V, VOUT = 1.8V, IOUT = 800 mA (20 MHz BW)
< 20mVP–P
Burst Mode - VIN = 3.3V, VOUT = 1.8V
<100 mA ± 20 mA
Pulse-Skip - VIN = 3.3V, VOUT = 1.8V
<100 mA ± 20 mA
2.25 MHz
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1025
800MA MONOLITHIC SYNCHRONOUS BUCK REGULATOR
QUICK START PROCEDURE
Demonstration Circuit 1025 is easy to set up to evaluate the performance of the LTC3560. 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 JP1, which connects the RUN pin to ground
(GND), and thus, shuts down the circuit, the pulseskip position of header JP2, and the 1.8V output voltage header – JP5.
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 DC1025 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 1 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
1.8V +/- 2% (1.764V to 1.836V).
Vary the input voltage from 2.5V to 5.5V and adjust
the load current from 0 to 800 mA. Vout should read
between 1.2V +/- 4% (1.728V to 1.872V).
Measure the output ripple voltage at any output current level; it usually will measure less than 30 mVAC.
Observe the voltage waveform at the switch node.
Verify the switching frequency is between 1.8 MHz
and 2.7 MHz (T = 0.555 us and 0.37 us), and that the
switch node waveform is rectangular in shape.
Insert the JP1 shunt into the OFF position and move
the 1.8V Vout JP5 shunt into any of the two remaining output voltage option headers: 1.2V or 1.5V. Just
as in the 1.8Vout 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 by inserting the
shunt in header JP1 into the OFF position (connecting
the RUN pin to ground).
2
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1025
800MA MONOLITHIC SYNCHRONOUS BUCK REGULATOR
Demonstration circuit 1025 is a step-down converter based on the LTC3560 monolithic synchronous buck
regulator. The DC1025 is easy to set up and evaluate the performance of the LTC3560. Refer to Figure 1 for
proper equipment set-up.
_
+
VOUT
L
O
A
_
IOUT
A
+
+
_
IIN
_
V
V
A
+
+
+
_
_
D
Figure 1. Proper Equipment Measurement Set-Up
Figure 2. Measuring Input or Output Ripple
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VS
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1025
800MA MONOLITHIC SYNCHRONOUS BUCK REGULATOR
Normal Switching Frequency & Output Ripple Voltage Waveforms
Figure 3. Switch Waveform & Output Ripple Voltage
V = 3.3V, V = 1.8V, I = 800mA
IN
OUT
OUT
Trace 1: Switch Voltage (2 V/div)
Trace 3: Output Ripple Voltage (20 mV/div AC)
4
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1025
800MA MONOLITHIC SYNCHRONOUS BUCK REGULATOR
Load Step Response Waveform
Figure 4. Load Step Response
V = 3.3V, V = 1.8V, 720mA Load Step (80mA <-> 800mA)
IN
OUT
Trace 3: Output Voltage (200mV/div AC)
Trace 4: Output Current (500 mA/div)
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1025
800MA MONOLITHIC SYNCHRONOUS BUCK REGULATOR
6
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