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 lev-
els of performance, efficiency, and small solution size
attainable using this part in a buck-boost power sup-
ply. 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 out-
put 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 R
SENSE
, 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 PARAMETER CONDITIONS MIN TYP MAX UNITS
V
IN
Input Supply Range
1.8 5.5
V
OUT
Output Voltage 3.3
I
OUT
Output Current Range V
IN
= 2.4 –5.5V
0 1.5
I
OUT
Maximum Output Current V
IN
= 0.8V (linear interpolation from 0.8 –2.4V)
0.8
F
SW
Switching (Clock) Frequency
1.0 MHz
V
OUT P-P
Output Ripple V
IN
= 4.2V, I
OUT
= 1.5A (20MHz BW) 20 mV
P–P
I
REG
Output Regulation Line and Load (1.8-5.5V, 0-1.5A)
±0.4 %
P
OUT
/P
IN
Efficiency (see Figure 2) V
IN
=4.2V, I
OUT
= 1.5A
89
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.
The converter utilizes a proprietary 4-switch topology
to provide an output that is within the input voltage
range. It seamlessly transitions from buck, to buck-
boost, to boost modes of operation to maintain the
output as the input voltage goes from maximum to
minimum values.
LTC3533
3.3V, 1.5A Synchronous Buck-
Boost Converter