DC652A - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 652
HIGH EFFICIENCY, 3A MONOLITHIC SYNCHRONOUS BUCK REGULATOR
LTC3412A
DESCRIPTION
DC652 is a 3A high efficiency, high frequency buck converter, incorporating the LTC3412A monolithic synchronous regulator. The DC652 has an input voltage range
of 2.25V to 5.5V and an output voltage range from 0.8V
to 5V. The operating frequency range of the DC652 is
either set with an external resistor or synchronized to an
external clock, with a range between 300kHz and 4MHz.
These features make the DC652 ideal for use in Li-Ion
battery (2.7V to 4.2V) applications, such as PDAs, cell
phones, and digital cameras. The DC652 can deliver
high(er) power – up to 3A of output current – in a relatively small circuit, because of the high current power
switches (70mΩ of on-state resistance) on the
LTC3412A. The LTC3412A also incorporates OPTI-LOOP
compensation, so that the DC652 can be optimized to
provide fast transient response over a wide range of line
and load conditions. Extra features include tracking, for
easy power supply sequencing, and Burst-ModeTM capability, for those circuits that operate during intervals of
low output power. All these features make the DC652
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.
LTC and Burst-Mode are trademarks of Linear Technology Corporation
Table 1.
Performance Summary (TA = 25°C)
PARAMETER
Minimum Input Voltage
CONDITION
VALUE
2.25V
Maximum Input Voltage
Output Voltage VOUT
Typical Output Ripple VOUT
Output Regulation
Nominal Switching Frequency
5.5V
VIN = 2.25V to 5.5V, IOUT = 0A to 3A
1.8V ±4%
VIN = 5V, IOUT = 3A (20MHz BW)
20mVP–P
Line
±1%
Load
±1%
RT = 309k
1MHz
QUICK START PROCEDURE
The DC652 demonstration board is easy to set up to
evaluate the performance of the LTC3412A. For
proper measurement equipment configuration, set up
the circuit according to the diagram in Figure 1. Before proceeding to test, insert jumper J2 shunt into
the off (lower) position, connecting the RUN pin to
ground (GND), which 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
1
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 652
HIGH EFFICIENCY, 3A MONOLITHIC SYNCHRONOUS BUCK REGULATOR
across the Vin or Vout and GND terminals. See
Figure 2 for proper scope probe technique.
6.
Measure the output ripple voltage at any output
current level; it should measure less than 20mVAC.
1.
Connect the input power supply and the load to the
board. Do not hot-plug Vin or increase Vin over
the rated maximum supply voltage of 5.5V, or the
part may be damaged. Refer to figure 1 for the
proper measurement equipment setup.
7.
Observe the voltage waveform at the switch node.
Verify the switching frequency is between 0.88MHz
and 1.12MHz (T = 1.13us and 0.893us), and that
the switch node waveform is rectangular in shape.
2.
Insert shunts into the Force Continuous position of
jumper J1, and into the 1.8V output voltage position.
3.
Apply 3.3V at Vin. Measure Vout; it should read
0V. If desired, one can measure the shutdown
supply current at this point. The supply current
will be approximately 1uA in shutdown.
4.
Turn on the circuit by inserting the shunt in jumper
J2 into the ON (upper) position. The output voltage
should be regulating. Measure Vout - it should
measure 1.8V +/- 2% (1.764V to 1.836V).
5.
Vary the input voltage from 2.25V to 5.5V and adjust the load current from 0 to 3A. Vout should
read between 1.8V +/- 4% (1.728V to 1.872V).
Insert jumper J2 shunt into the OFF position and move
the 1.8V Vout shunt into any of the remaining output
voltage options: 2.5V or 3.3V. Re-insert jumper J2
shunt into the ON position. Just as in the 1.8Vout test,
the output voltage should read Vout +/- 2% tolerance
under static line and load conditions, and another +/- 2%
tolerance under dynamic line and load conditions (+/4% total). The Burst-ModeTM capability of the
LTC3412A can also be observed now by changing the
J3 jumper shunt from the Force Continuous (upper)
position to the Burst-ModeTM (lower) position.
When finished, turn off the circuit (connecting the
RUN pin to ground) by inserting the shunt in jumper
J2 into the OFF (lower) position.
2
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 652
HIGH EFFICIENCY, 3A MONOLITHIC SYNCHRONOUS BUCK REGULATOR
Figure 1. Proper Measurement Equipment Setup
Figure 2. Measuring Input or Output Ripple
3
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 652
HIGH EFFICIENCY, 3A MONOLITHIC SYNCHRONOUS BUCK REGULATOR
Figure 3. Load Step Response
VIN = 3.3V, VOUT = 2.5V, 2A Load Step
Trace 1: Output Voltage (100mV/div AC)
Trace 2: Output Current (1A/div)
4
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 652
HIGH EFFICIENCY, 3A MONOLITHIC SYNCHRONOUS BUCK REGULATOR
5
Similar pages