LTC3129 datasheet(16/30 Pages) LINER

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LTC3129

3129fc

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operaTion

Figure 4. Typical 2-Layer PC Board Layout (MSE Package)

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 VCC.

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 VCC regulator can also generate wasted

heat when VIN is very high, adding to the total power

dissipation of the IC. As described elsewhere in this data

sheet, bootstrapping of the VCC for 5V output applications

can essentially eliminate the VCC 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.

IftheICdietemperatureexceedsapproximately180°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

VIN

VCC

GND

VOUT

COUT

CIN

3129 F04

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