DC768A - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 768
15A POLYPHASE MONOLITHIC SYNCHRONOUS BUCK REGULATOR
LTC3415
DESCRIPTION
Demonstration Circuit 768 is a 15A high efficiency,
phase lockable constant frequency buck converter, incorporating two LTC3415 polyphase monolithic synchronous regulators. The DC768 has an input voltage
range of 2.5V 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 DC768 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 DC768 can deliver
high power for monolithic parts – up to 15A of output
current – due to the high current power switches (28
mΩ of on-state resistance) of the LTC3415. The
LTC3415 also incorporates OPTI-LOOP compensation,
so that the DC768 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 DC768 has two
LTC3415s operating in polyphase operation. Due to the
LTC3415 polyphase capability, multiple DC768s can be
paralleled for higher current power supplies. Since the
parallel LTC3415s operate out-of-phase, the amount of
input and output capacitance required will be minimal.
The DC768 offers the three standard modes of operation: force continuous, pulse-skipping, and BurstModeTM, 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 DC768. All these features make the DC768 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
Table 1.
Performance Summary (TA = 25°C)
PARAMETER
CONDITIONS
VALUE
Minimum Input Voltage
2.5V
Maximum Input Voltage
5.5V
1.2V ±3% (1.164V to 1.236V)
Output Voltage VOUT Regulation
VIN = 2.5V to 5.5V, IOUT = 0A to 15A
1.5V ±3% (1.455V to 1.545V)
1.8V ±3% (1.746V to 1.854V)
Typical Output Ripple VOUT
Operation Modes
Nominal Switching Frequency
VIN = 5V, IOUT = 15A (20 MHz BW)
<20mVP–P
Burst Mode - VIN = 3.3V, VOUT = 1.8V
<1.5A ±0.1A
Pulse-Skipping - VIN = 3.3V, VOUT = 1.8V
< 5A ±0.1A
Forced Continuous
Any Output Current
1.5 MHz
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 768
15A POLYPHASE MONOLITHIC SYNCHRONOUS BUCK REGULATOR
QUICK START PROCEDURE
Demonstration Circuit 768 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 position, which connects the RUN
pin to ground (GND), and thus, shuts down the circuit.
NOTE: 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 technique.
1.
2.
With the DC768 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 400 uA, or less, in
shutdown.
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 1.2V +/- 1.5% (1.182V to 1.218V).
3.
Vary the input voltage from 2.5V to 5.5V and adjust
the load current from 0 to 15A. Vout should read
between 1.2V +/- 3% (1.164V to 1.236V).
4.
Measure the output ripple voltage at any output
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 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 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 repositioning 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 header
JP5 into the OFF position.
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 768
15A POLYPHASE MONOLITHIC SYNCHRONOUS BUCK REGULATOR
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)
Synchronized to 2Vpk-to-pk, 2 MHZ signal injected into the PLLPF
pin - VIN = 3.3V, VOUT = 1.8V
2 MHZ (Measured at SW
& CLOCKOUT Pins)
CLOCKIN
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 768
15A 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 768
15A POLYPHASE MONOLITHIC SYNCHRONOUS BUCK REGULATOR
Figure 3. Load Step Response
V = 3.3V, V = 1.8V & 10A Load Step
IN
OUT
Trace 1: Output Voltage (100mV/div AC)
Trace 2: Output Current (5A/div)
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 768
15A POLYPHASE MONOLITHIC SYNCHRONOUS BUCK REGULATOR
Figure 4.
180°° Out-of-Phase Switching Operation
VIN – 3.3V, VOUT – 1.2V, IOUT – 5A
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 768
15A POLYPHASE MONOLITHIC SYNCHRONOUS BUCK REGULATOR
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