LTC3129_15 Datasheet, PDF (16/30 Pages) Linear Technology – 15V, 200mA Synchronous Buck-Boost DC/DC Converter with 1.3A Quiescent Current

LTC3129
OPERATION
The MPPC pin controls the converter in a linear fashion
when using sources that can provide a minimum of 5mA
to 10mA of continuous input current. For operation from
weaker input sources, refer to the Applications Informa-
tion section to see how the programmable RUN pin can
be used to control the converter in a hysteretic manner to
provide an effective MPPC function for sources that can
provide as little as 5µA or less. If the MPPC function is not
required, the MPPC pin should be tied to V_CC.
Thermal Considerations
The power switches of the LTC3129 are designed to oper-
ate continuously with currents up to the internal current
limit thresholds. However, when operating at high current
levels, there may be significant heat generated within the
IC. In addition, the V_CC regulator can also generate wasted
heat when V_IN is very high, adding to the total power
dissipation of the IC. As described elsewhere in this data
sheet, bootstrapping of the V_CC for 5V output applications
can essentially eliminate the V_CC power dissipation term
and significantly improve efficiency. As a result, careful
consideration must be given to the thermal environment
of the IC in order to provide a means to remove heat from
the IC and ensure that the LTC3129 is able to provide its
full rated output current. Specifically, the exposed die
attach pad of both the QFN and MSE packages must be
soldered to a copper layer on the PCB to maximize the
conduction of heat out of the IC package. This can be ac-
complished by utilizing multiple vias from the die attach
pad connection underneath the IC package to other PCB
layer(s) containing a large copper plane. A typical board
layout incorporating these concepts is shown in Figure 4.
If the IC die temperature exceeds approximately 180°C, over
temperature shutdown will be invoked and all switching
will be inhibited. The part will remain disabled until the die
temperature cools by approximately 10°C. The soft-start
circuit is re-initialized in overtemperature shutdown to
provide a smooth recovery when the IC die temperature
cools enough to resume operation.
GND
V_CC
V_IN
C_IN
L
C_OUT
GND
V_OUT
3129 F04
Figure 4. Typical 2-Layer PC Board Layout (MSE Package)
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