QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1176
1.25A, 4 MHZ SYNCHRONOUS STEP-DOWN DC/DC CONVERTER
1
LTC3411A
DESCRIPTION
Demonstration circuit 1176 is a step-down con-
verter, using the LTC3411A monolithic synchronous
buck regulator. The DC1176 has an input voltage
range of 2.5V to 5.5V, and is capable of delivering
up to 1.25A of output current. The output voltage of
the DC1176 can be set as low as 0.8V, the reference
voltage of the LTC3411A. At low load currents, the
DC1176 can operate in either noise sensitive appli-
cations, due to the capability of the LTC3411A to
operate in pulse-skipping mode, or in high effi-
ciency applications, because the LTC3411A can also
operate in Burst-Mode®. During Burst-Mode® op-
eration, the output ripple voltage is still low – less
than 20 mV – due to the improvements made in the
design of the LTC3411A. Of course, in continuous
mode, or large load current applications, the
DC1176 is a high efficiency circuit - over 95%.
The DC1176 consumes less than 60 uA of quies-
cent current during sleep operation, and during
shutdown, it consumes less than 1 uA. Because of
the high switching frequency of the LTC3411A,
which is programmable up to 4 MHz, the DC1176
uses low profile surface mount components.
These features, plus the LTC3411A coming in a
small 10-Lead DFN or MS package, make the
DC1176 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 2.5V
Maximum Input Voltage 5.5V
GND = Shutdown
Run/Shutdown VIN = Run
1.8V ±4% (1.728V – 1.872V)
2.5V ±4% (2.4V - 2.6V)
Output Voltage VOUT
VIN = 2.5V to 5.5V, IOUT = 0A to 1.25A
3.3V ±4% (3.168V – 3.432V)
Typical Output Ripple VOUT VIN = 3.3V, VOUT = 1.8V, IOUT = 1.25A (20 MHz BW) < 20mVP–P
Burst Mode - VIN = 3.3V, VOUT = 1.8V < 250 mA
Operation Modes
Pulse-Skip - VIN = 3.3V, VOUT = 1.8V < 200 mA
Nominal Switching Frequency RT = 549k 1 MHz
±
20%
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1176
1.25A, 4 MHZ SYNCHRONOUS STEP-DOWN DC/DC CONVERTER
2
QUICK START PROCEDURE
Demonstration Circuit 1176 is easy to set up to evalu-
ate the performance of the LTC3411A. 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 pulse-
skip position of header JP1, and the 1.8V output volt-
age 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 volt-
age 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 DC1176 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.
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 2.5V to 5.5V and adjust
the load current from 0 to 1.25A. 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 cur-
rent to any current less than 200 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. Change the JP1 shunt
from pulse-skip mode to Burst Mode®. Observe the
Burst Mode® of operation at the switch node, and
measure the output ripple voltage. It should measure
less than 100 mV.
Insert the JP3 shunt into the OFF position and move
the 1.8V Vout JP2 shunt into any of the two remain-
ing output voltage option headers: 2.5V or 3.3V. Just
as in the 1.8Vout test, the output voltage should read
Vout +/- 2% tolerance under static line and load con-
ditions, and +/- 1% tolerance under dynamic line and
load conditions (+/- 2% total). Also, circuit operation
in either Burst Mode® or pulse-skip 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).
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1176
1.25A, 4 MHZ SYNCHRONOUS STEP-DOWN DC/DC CONVERTER
3
Figure 1.
Figure 1.Figure 1.
Figure 1. Proper Equipment Measurement Set
Proper Equipment Measurement SetProper Equipment Measurement Set
Proper Equipment Measurement Set-
--
-Up
UpUp
Up
Figure 2.
Figure 2.Figure 2.
Figure 2. Measuring Input or Output Ri
Measuring Input or Output RiMeasuring Input or Output Ri
Measuring Input or Output Rip
pp
pple
pleple
ple
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1176
1.25A, 4 MHZ SYNCHRONOUS STEP-DOWN DC/DC CONVERTER
4
Normal Switching Frequency & Output Ripple Voltage
Normal Switching Frequency & Output Ripple Voltage Normal Switching Frequency & Output Ripple Voltage
Normal Switching Frequency & Output Ripple Voltage
Waveforms
WaveformsWaveforms
Waveforms
Figure 3.
Figure 3.Figure 3.
Figure 3. Switch Waveform & Out
Switch Waveform & OutSwitch Waveform & Out
Switch Waveform & Output Ripple Voltage
put Ripple Voltageput Ripple Voltage
put Ripple Voltage
V
VV
V
IN
ININ
IN
= 5
= 5 = 5
= 5V, V
V, VV, V
V, V
OUT
OUTOUT
OUT
= 2.5
= 2.5 = 2.5
= 2.5V, I
V, IV, I
V, I
OUT
OUTOUT
OUT
= 1.
= 1. = 1.
= 1.25
2525
25A
AA
A
Trace 2
Trace 2Trace 2
Trace 2: Switch Voltage (2 V/div)
: Switch Voltage (2 V/div): Switch Voltage (2 V/div)
: Switch Voltage (2 V/div)
Trace 3: Output Ripple Voltage (20 mV/div AC)
Trace 3: Output Ripple Voltage (20 mV/div AC)Trace 3: Output Ripple Voltage (20 mV/div AC)
Trace 3: Output Ripple Voltage (20 mV/div AC)
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1176
1.25A, 4 MHZ SYNCHRONOUS STEP-DOWN DC/DC CONVERTER
5
Load Step Response Waveform
Load Step Response WaveformLoad Step Response Waveform
Load Step Response Waveform
Figure 4.
Figure 4.Figure 4.
Figure 4. Load Step Response
Load Step ResponseLoad Step Response
Load Step Response
V
VV
V
IN
ININ
IN
= 3.3V, V
= 3.3V, V = 3.3V, V
= 3.3V, V
OUT
OUTOUT
OUT
= 1.8V, 1.
= 1.8V, 1. = 1.8V, 1.
= 1.8V, 1.1
11
12
22
25
55
5A Load Step (
A Load Step (A Load Step (
A Load Step (1
11
125
2525
25mA <
mA <mA <
mA <-
--
-> 1.
> 1.> 1.
> 1.25
2525
25A)
A)A)
A)
Pulse
PulsePulse
Pulse-
--
-Skip Mode Fsw =
Skip Mode Fsw = Skip Mode Fsw =
Skip Mode Fsw = 1 MHz
1 MHz1 MHz
1 MHz
Trace 3: Output Voltage (10
Trace 3: Output Voltage (10Trace 3: Output Voltage (10
Trace 3: Output Voltage (100mV/div AC)
0mV/div AC)0mV/div AC)
0mV/div AC)
Trace 4: Output Current (0.5
Trace 4: Output Current (0.5Trace 4: Output Current (0.5
Trace 4: Output Current (0.5A/div)
A/div)A/div)
A/div)
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1176
1.25A, 4 MHZ SYNCHRONOUS STEP-DOWN DC/DC CONVERTER
6
