LTC3536_15 Datasheet, PDF (23/28 Pages) Linear Technology – 1A Low Noise, Buck-Boost DC/DC Converter

LTC3536
Applications Information
Switching Frequency Selection
Higher switching frequencies facilitate the use of smaller
inductors as well as smaller input and output filter capaci-
tors which results in a smaller solution size and reduced
component height. However, higher switching frequencies
also generally reduce conversion efficiency due to the
increased switching losses. In addition, the maximum
voltage step-up ratio is reduced slightly at higher switching
frequencies as shown in the maximum duty cycle versus
switching frequency curve in the Typical Performance
Characteristics section of this data sheet.
PCB Layout Considerations
The LTC3536 buck-boost converter switches large currents
at high frequencies. Special attention should be paid to the
PC board layout to ensure a stable, noise-free and efficient
application circuit. A few key guidelines are provided:
1. The parasitic inductance and resistance of all circulating
high current paths should be minimized. This can be
accomplished by keeping the routes as short and as
wide as possible. Capacitor ground connections should
via down to the ground plane by way of the shortest
route possible. The bypass capacitors on PV_IN and
V_OUT should be placed as close to the IC as possible
and should have the shortest possible paths to ground.
2. The exposed pad is the electrical power ground connec-
tion for the LTC3536 in the DD package. Multiple vias
should connect the backpad directly to the ground plane.
In addition, maximization of the metallization connected
to the backpad will improve the thermal environment
and improve the power handling capabilities of the IC
in either package.
3. The components their connections with high current
should all be placed over a complete ground plane to
minimize loop cross-sectional areas. This minimizes
EMI and reduces inductive drops.
4. Connections to all of the components with high current
should be made as wide as possible to reduce the series
resistance. This will improve efficiency and maximize the
output current capability of the buck-boost converter
5. To prevent large circulating currents in the ground plane
from disrupting operation of the LTC3536, all small-
signal grounds should return directly to GND by way
of a dedicated Kelvin route. This includes the ground
connection for the RT pin resistor and the ground con-
nection for the feedback network.
6. Keep the routes connecting to the high impedance,
noise sensitive inputs FB and RT as short as possible
to reduce noise pick-up. Example from MODE route in
case the chip is synchronized with external clock.
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