QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1015
2.5A, 10V, MONOLITHIC SYNCHRONOUS STEP-DOWN REGULATOR
LTC3602
DESCRIPTION
Demonstration circuit 1015 is a step-down con-
verter, using the LTC3602 monolithic synchronous
buck regulator. The DC1015 has an input voltage
range of 4.5V to 10V, and is capable of delivering up
to 2.5A of output current. The output voltage of the
DC1015 can be set as low as 0.6V, the reference
voltage of the LTC3602. At low load currents, the
DC1015 can operate in either noise sensitive appli-
cations, due to the capability of the LTC3602 to op-
erate in pulse-skipping mode, or in high efficiency
applications, because the LTC3602 can also operate
in Burst-Mode®. Of course, in continuous mode,
or large load current applications, the DC1015 is a
high efficiency circuit - over 90%. The DC1015
consumes less than 75 uA of quiescent current
during sleep operation typically, and during shut-
down, it consumes less than 1 uA. Because of the
high switching frequency of the LTC3602, which is
programmable up to 3 MHz, the DC1015 uses low
profile surface mount components. These fea-
tures, plus the LTC3602 coming in a 20-Lead QFN
package, make the DC1015 an ideal circuit for use
in high voltage portable, battery-powered applica-
tions.
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
Minimum Input Voltage
Maximum Input Voltage
Run/Shutdown
CONDITIONS
VALUE
4.5V
10V
GND = Shutdown
VIN = Run
2.5V ±4% (2.4V – 2.6V)
Output Voltage VOUT Regulation
VIN = 4.5V to 10V, 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 = 10V, VOUT = 5V, IOUT = 2.5A (20 MHz BW)
Burst Mode - VIN = 8.4V, VOUT = 3.3V
Pulse-Skip - VIN = 8.4V, VOUT = 3.3V
RT = 105k
< 20mVP–P
< 1.25 A
< 650 mA
1 MHz
1
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1015
2.5A, 10V, MONOLITHIC SYNCHRONOUS STEP-DOWN REGULATOR
QUICK START PROCEDURE
Demonstration Circuit 1015 is easy to set up to evalu-
ate the performance of the LTC3602. 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 position of header JP6, the external soft-
start position of header JP7, and the 3.3V 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 DC1015 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 10V, 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 10V 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 8.4V
and the output current to any current less than 1.25A.
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 625 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 dy-
namic line and load conditions (+/- 2% total). Also,
the 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 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 2.2 uH on the DC1015 should be
changed to 1 uH. This is required so that the induc-
tor ripple current “ramp” waveform has a large
enough slope for the current comparator (to distin-
guish
it
from
noise
voltages).
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Talking
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