DC999A - Demo Manual

DEMO CIRCUIT 999A
LTC3533
QUICK START
GUIDE
LTC3533
3.3V, 1.5A Synchronous BuckBoost Converter
DESCRIPTION
Demonstration circuit 999A is a wide input range, 3.3V,
1.5A Synchronous Buck-Boost Converterfeaturing the
LTC3533.
This circuit was designed to demonstrate the high levels of performance, efficiency, and small solution size
attainable using this part in a buck-boost power supply. It operates at 1.0MHz and produces a regulated
3.3V, 1.5A output from an input voltage range of 2.4
to 5.5V, and operates down to 1.8V with de-rated output current. It is suitable for portable applications, and
has a footprint area that is 0.25 square inches.
Synchronous rectification helps to attain efficiency up
to 94%, depending on line and load. The LTC3533
provides current limit and shutdown disconnect. It
offers Burst Mode operation for high efficiency at light
loads.
Design files for this circuit board are available. Call
the LTC factory.
, LTC, LTM, LT, Burst Mode, OPTI-LOOP, Over-The-Top and PolyPhase are registered
trademarks of Linear Technology Corporation. Adaptive Power, C-Load, DirectSense, Easy
Drive, FilterCAD, Hot Swap, LinearView, µModule, Micropower SwitcherCAD, Multimode
Dimming, No Latency ∆Σ, No Latency Delta-Sigma, No RSENSE, Operational Filter, PanelProtect,
PowerPath, PowerSOT, SmartStart, SoftSpan, Stage Shedding, SwitcherCAD, ThinSOT,
UltraFast and VLDO are trademarks of Linear Technology Corporation. Other product names
may be trademarks of the companies that manufacture the products.
PERFORMANCE SUMMARY Specifications are at TA = 25°C
SYMBOL
VIN
VOUT
IOUT
IOUT
FSW
VOUT P-P
IREG
POUT/PIN
PARAMETER
Input Supply Range
Output Voltage
Output Current Range
Maximum Output Current
Switching (Clock) Frequency
Output Ripple
Output Regulation
Efficiency (see Figure 2)
CONDITIONS
MIN
1.8
TYP
MAX
5.5
3.3
VIN = 2.4 –5.5V
VIN = 0.8V (linear interpolation from 0.8 –2.4V)
VIN = 4.2V, IOUT = 1.5A (20MHz BW)
Line and Load (1.8-5.5V, 0-1.5A)
VIN =4.2V, IOUT = 1.5A
0
1.5
0.8
1.0
20
±0.4
89
UNITS
V
V
A
A
MHz
mVP–P
%
%
OPERATING PRINCIPLES
The LTC3533 Synchronous Buck-Boost Converter is
employed to produce a 3.3V output from an input
ranging from 1.8V to 5.5V.
range. It seamlessly transitions from buck, to buckboost, to boost modes of operation to maintain the
output as the input voltage goes from maximum to
minimum values.
The converter utilizes a proprietary 4-switch topology
to provide an output that is within the input voltage
1
LTC3533
QUICK START PROCEDURE
Demonstration circuit 999 is easy to set up to evaluate
the performance of the LTC3533. Refer to Figure 1 for
proper measurement equipment setup and follow the
procedure below:
NOTE. When measuring the output voltage ripple, care must be taken to
avoid a long ground lead on the oscilloscope probe. Measure the output
voltage ripple by touching the probe tip and ground ring directly across
the last output capacitor (COUT) as shown in Figure 1.
1. Set an input power supply that is capable of 1.8V to
5.5V to 4.2V. Turn off the supply.
NOTE. Make sure that the input voltage never exceeds 5.5V.
4. Check for the proper output voltage of 3.3V. Turn
off the power at the input.
5. Once the proper output voltages are established,
connect a variable load capable of sinking 1.5A at
3.3V to the output terminals +Vout and –Vout. Set
the current for 0A.
a.
If efficiency measurements are desired, an ammeter or a resistor shunt that is capable of handling 1.5Adc can be put in series with the output load in order to measure the DC999A’s output current.
b.
A voltmeter with a capability of measuring at
least 3.3V can be placed across the output terminals in order to get an accurate output voltage measurement.
2. With power off, connect the supply to the input
terminals +Vin and –Vin.
a.
Input voltages lower than 1.8V can keep the
converter from turning on due to the undervoltage lockout feature of the LTC3533.
b.
If efficiency measurements are desired, an ammeter capable of measuring 3Adc or a resistor
shunt can be put in series with the input supply
in order to measure the DC999A’s input current.
c.
A voltmeter with a capability of measuring at
least 5.5V can be placed across the input terminals in order to get an accurate input voltage
measurement.
3. Turn on the power at the input.
2
6. Turn on the power at the input.
NOTE. If there is no output, temporarily disconnect the load to make
sure that the load is not set too high.
7. Once the proper output voltage is again established, adjust the load within the operating range
and observe the output voltage regulation, ripple
voltage, efficiency and other desired parameters.
LTC3533
Figure 1. Proper Measurement Equipment Setup
3
LTC3533
100
90
80
1.8Vin
2.4Vin
70
3.0Vin
4.2Vin
60
5.5Vin
1.8Vin(Burst)
50
2.4Vin(Burst)
3.0Vin(Burst)
40
4.2Vin(Burst)
5.5Vin(Burst)
30
20
10
1.00E-03
1.00E-02
1.00E-01
1.00E+00
1.00E+01
Figure 2. Efficiency – Note 90%+ efficiency over a wide current range.
4
LTC3533
Figure 3. Output Ripple at 2.6Vin and 1.5Aout (20MHz) - 1uS and 20mV / div
5
LTC3533
Figure 4. Transient Response Waveform at 4.2Vin and 0.75 - 1.5Aout – 500uS and 50mV / div
6
LTC3533
7
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