DC725A - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 725
7A POLYPHASE MONOLITHIC SYNCHRONOUS BUCK REGULATOR
LTC3415
DESCRIPTION
Demonstration Circuit 725 is a 7A high efficiency,
phase lockable constant frequency buck converter, incorporating the LTC3415 polyphase
monolithic synchronous regulator. The DC725
has an input voltage range of 2.375V to 5.5V and
an output voltage range from 0.6V to 5V. The reference voltage of 0.6V is +/-1% accurate, producing a more precise output voltage. The operating
frequency range of the DC725 is either set by the
LTC3415 internal oscillator to 1.5 MHz, set to 1
MHz or 2 MHz by forcing the PLLPF pin to ground
or Vin, respectively, or synchronized to an external
clock, with a range between 750 kHz and 2.25
MHz. The DC725 can deliver high power for a
monolithic part – up to 7A of output current – due
to the high current power switches (28 mΩ of onstate resistance) of the LTC3415. The LTC3415
also incorporates OPTI-LOOP compensation, so
that the DC725 can be optimized with external
components to provide fast transient response
over a wide range of line and load conditions.
However, the LTC3415 has internal compensation
for those requiring a simple high power supply
only. The LTC3415 can also do polyphase operation, which allows multiple DC725s to be used in
parallel for higher current power supplies. Since
the parallel LTC3415s can operate out-of-phase,
the amount of input and output capacitance required will be minimal. The DC725 offers the
three standard modes of operation: force continuous, pulse-skipping, and Burst-ModeTM, for those
circuits that operate during intervals of low output
power. Extra features include tracking, for easy
power supply sequencing, output margining,
power good, and spread spectrum operation,
which significantly reduces the peak switching
noise emitted from the DC725. All these features
make the DC725 perfectly suited for high current,
high power applications, such as notebook or
desktop computers.
Design files for this circuit board are available. Call the LTC factory.
TM - Burst Mode is a trademark of Linear Technology Corporation
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 725
7A POLYPHASE MONOLITHIC SYNCHRONOUS BUCK REGULATOR
Table 1.
Performance Summary (TA = 25°C)
PARAMETER
CONDITIONS
VALUE
Minimum Input Voltage
2.375V
Maximum Input Voltage
5.5V
1.2V ±3% (1.164V to
1.236V)
Output Voltage VOUT Regulation
VIN = 2.375V to 5.5V, IOUT = 0A to 7A
1.5V ±3% (1.455V to
1.545V)
1.8V ±3% (1.746V to
1.854V)
Typical Output Ripple VOUT
Operation Modes
VIN = 5V, IOUT = 7A (20 MHz BW)
<20mVP–P
Burst Mode - VIN = 3.3V, VOUT = 1.8V
<1.6A ±0.1A%
Pulse-Skipping - VIN = 3.3V, VOUT = 1.8V
<1.5A ±0.1A%
Forced Continuous
Any Output Current
Nominal Switching Frequency
1.5 MHz
QUICK START PROCEDURE
Demonstration Circuit 725 is easy to set up to
evaluate the performance of the LTC3415. For
proper measurement equipment configuration,
set up the circuit according to the diagram in
Figure 1. Before proceeding to test, make sure
the jumper shunts are in the appropriate header
according to the legend in Figure 1, except for
one exception: insert jumper JP5 shunt into the
off (upper) position, which connects the RUN
pin to ground (GND), and thus, shuts down the
circuit.
1. With the DC725 set up according to the
NOTE: When measuring the input or output volt-
header JP5 into the ON (lower) position. The
output voltage should be regulating. Measure Vout - it should measure 1.2V +/- 1.5%
(1.182V to 1.218V).
age 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 technique.
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.
2. Turn on the circuit by inserting the shunt in
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 725
7A POLYPHASE MONOLITHIC SYNCHRONOUS BUCK REGULATOR
3. Vary the input voltage from 2.375V to 5.5V
and adjust the load current from 0 to 7A. Vout
should read between 1.2V +/- 3% (1.164V to
1.236V).
4. Measure the output ripple voltage at any out-
put 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 1.3 MHz and 1.7 MHz (T = 0.769 us
and 0.588 us), and that the switch node
Vout +/- 1.5% tolerance under static line and load
conditions, and another +/- 1.5% tolerance under
dynamic line and load conditions (+/- 3% total).
The Burst-ModeTM or pulse-skipping operation
modes of the LTC3415 can also be observed
now by changing the position of the shunt in
header JP7. 1 or 2 MHz operating frequencies
can be activated by re-positioning the JP6
shunt. The tables below show the extra features, such as margining and spread spectrum.
When finished, turn off the circuit (connecting
the RUN pin to ground) by inserting the shunt in
PARAMETER
CONDITIONS
VALUE
CLOCKOUT
PHMODE Pin Pulled to VIN - VIN = 3.3V, VOUT = 1.8V
1.5 MHz
CLOCKIN Pin Connected to VIN - VIN = 3.3V, VOUT = 1.8V
Spread Spectrum (See
Photo)
CLOCKIN
Synchronized to 2Vpk-to-pk, 2 MHZ signal injected into the PLLPF 2 MHZ (Measured at SW
pin - VIN = 3.3V, VOUT = 1.8V
& CLOCKOUT Pins)
header JP5 into the OFF (upper) position.
waveform is rectangular in shape.
Insert jumper JP5 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
PARAMETER
CONDITIONS
POSITION MGN
MGN+
Margining
VIN = 3.3V, VOUT = 1.8V, IOUT
= 5A
MGN-
POSITION BSEL
VALUE
5%
1.89V ±4% (1.814V to
1.966V)
10%
1.98V ±4% (1.900V to
2.060V)
15%
2.07V ±4% (1.987V to
2.153V)
5%
1.71V ±4% (1.641V to
1.779V)
10%
1.62V ±4% (1.555V to
1.685V)
15%
1.53V ±4% (1.468V to
1.592V)
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 725
7A POLYPHASE MONOLITHIC SYNCHRONOUS BUCK REGULATOR
Figure 1. Proper Measurement Equipment Setup
Figure 2. Measuring Input or Output Ripple
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 725
7A POLYPHASE MONOLITHIC SYNCHRONOUS BUCK REGULATOR
Figure 3. Load Step Response
VIN = 3.3V, VOUT = 1.8V & 5A Load Step
Trace 1: Output Voltage (100mV/div AC)
Trace 2: Output Current (2A/div)
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 725
7A POLYPHASE MONOLITHIC SYNCHRONOUS BUCK REGULATOR
Figure 4. Normal Switching Operation vs. Spread Spectrum Operation
VIN – 3.3V, VOUT – 1.8V, IOUT – 5A
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 725
7A POLYPHASE MONOLITHIC SYNCHRONOUS BUCK REGULATOR
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