DC1206A - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1206
1.8A, 4 MHZ SYNCHRONOUS STEP-DOWN DC/DC CONVERTER
LTC3568
DESCRIPTION
Demonstration circuit 1206 is a step-down converter, using the LTC3568 monolithic synchronous
buck regulator. The DC1206 has an input voltage
range of 2.25V to 5.5V, and is capable of delivering
up to 1.8A of output current at a minimum input
voltage of 2.25V. The output voltage of the DC1206
can be set as low as 0.8V, the reference voltage of
the LTC3568. At low load currents, the DC1206 can
operate in either noise sensitive applications, due to
the capability of the LTC3568 to operate in pulseskipping mode, or in high efficiency applications,
because the LTC3568 can also operate in BurstMode®. During Burst-Mode® operation, the output ripple voltage is still low – less than 30 mV –
due to the improvements made in the design of the
LTC3568. Of course, in continuous mode, or large
load current applications, the DC1206 is a high
efficiency circuit - over 95%. The DC1206 consumes less than 70 uA of quiescent current during
sleep operation typically, and during shutdown, it
consumes less than 1 uA. Because of the high
switching frequency of the LTC3568, which is programmable up to 4 MHz, the DC1206 uses low
profile surface mount components. These features, plus the LTC3568 coming in a small 10-Lead
DFN package, make the DC1206 an ideal circuit for
use in battery-powered, hand-held 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
2.25V
Maximum Input Voltage
5.5V
GND = Shutdown
Run/Shutdown
VIN = Run
1.2V ±4% (1.152V – 1.248V)
Output Voltage VOUT
VIN = 2.25V to 5.5V, IOUT = 0A to 1.8A
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 = 1.8A (20 MHz BW)
< 20mVP–P
Burst Mode - VIN = 3.3V, VOUT = 1.8V
< 500 mA
Pulse-Skip - VIN = 3.3V, VOUT = 1.8V
< 425 mA
RT = 324k
1 MHz
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1206
1.8A, 4 MHZ SYNCHRONOUS STEP-DOWN DC/DC CONVERTER
QUICK START PROCEDURE
Demonstration Circuit 1206 is easy to set up to evaluate the performance of the LTC3568. 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 JP3, which connects the RUN pin to ground
(GND), and thus, shuts down the circuit, the pulseskip position of header JP1, and the 1.8V 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 DC1206 set up according to the proper
measurement and equipment set-up 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. Turn on the circuit by inserting the shunt in
header JP3 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 2.25V to 5.5V and adjust
the load current from 0 to 1.8A. Vout should read
1.8V +/- 4% (1.728V to 1.872V).
Adjust the output current to 1A. Measure the output
ripple voltage; it will measure less than 20 mVAC.
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 0.869 us), and that
the switch node waveform is rectangular in shape.
Adjust the input voltage to 3.3V and the output current to any current less than 400 mA. Observe the
pulse-skip mode of operation at the switch node.
Also, measure the output ripple voltage; it should
measure less than 20 mV. Change the JP1 shunt
from pulse-skip mode to Burst Mode®. Observe the
Burst Mode® operation at the switch node, and
measure the output ripple voltage. It should measure
less than 50 mV.
Insert the JP3 shunt into the OFF position and move
the 1.8V Vout JP2 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). Also, circuit operation
in either Burst Mode® or pulse-skip mode will be the
same.
When finished, turn off the circuit by inserting the
shunt in header JP3 into the OFF position (connecting
the RUN pin to ground).
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1206
1.8A, 4 MHZ SYNCHRONOUS STEP-DOWN DC/DC CONVERTER
Figure 1. Proper Equipment Measurement Set-Up
Figure 2. Measuring Input or Output Ripple
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1206
1.8A, 4 MHZ SYNCHRONOUS STEP-DOWN DC/DC CONVERTER
Normal Switching Frequency & Output Ripple Voltage
Waveforms
Figure 3. Switch Waveform & Output Ripple Voltage
V = 3.3V, V = 1.8V, I = 1.8A
IN
OUT
OUT
Trace 2: Switch Voltage (2 V/div)
Trace 3: Output Ripple Voltage (20 mV/div AC)
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1206
1.8A, 4 MHZ SYNCHRONOUS STEP-DOWN DC/DC CONVERTER
Load Step Response Waveform
Figure 4. Load Step Response
V = 3.3V, V = 1.8V, 1.62A Load Step (180mA <-> 1.8A)
IN
OUT
Pulse-Skip Mode Fsw = 1 MHz
Trace 3: Output Voltage (50mV/div AC)
Trace 4: Output Current (1A/div)
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1206
1.8A, 4 MHZ SYNCHRONOUS STEP-DOWN DC/DC CONVERTER
6
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