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LT8330

8330fa

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applicaTions inForMaTion

THERMAL CONSIDERATIONS

Care should be taken in the layout of the PCB to ensure

good heat sinking of the LT8330. The DFN package has the

best thermal performance due to an exposed pad (Pin 9)

on the bottom of the package. This exposed pad must be

soldered to a ground plane. Pin 5 of the DFN package (and

Pin 2 of the TSOT package) should also be connected to a

ground plane. The ground plane should be connected to

largecopperlayerstospreadheatdissipatedbytheLT8330

and to further reduce the thermal resistance (θJA) values

listed in the Pin Configuration section. Power dissipation

within the LT8330 (PDISS_LT8330) can be estimated by

subtracting the inductor and Schottky diode power losses

from the total power losses calculated in an efficiency

measurement. The junction temperature of LT8330 can

then be estimated by,

TJ (LT8330) = TA + θJA • PDISS_LT8330

ADDITIONAL TOPOLOGIES : SEPIC AND INVERTING

In addition to the Boost topology, the LT8330 can be

configured in a SEPIC or Inverting topology. SEPIC and

Inverting converters are analyzed below.

SEPIC CONVERTER APPLICATIONS

The LT8330 can be configured as a SEPIC (single-ended

primary inductance converter), as shown in Figure 5. This

topology allows for the input to be higher, equal, or lower

than the desired output voltage. The conversion ratio as

a function of duty cycle is:

VOUT + VD

VIN

1−D

in continuous conduction mode (CCM).

In a SEPIC converter, no DC path exists between the input

and output. This is an advantage over the boost converter

for applications requiring the output to be disconnected

from the input source when the circuit is in shutdown.

SEPIC Converter: Switch Duty Cycle and Frequency

For a SEPIC converter operating in CCM, the duty cycle

of the main switch can be calculated based on the output

voltage (VOUT), the input voltage (VIN) and the diode

forward voltage (VD).

Themaximumdutycycle(DMAX)occurswhentheconverter

operates at the minimum input voltage:

DMAX =

VOUT + VD

VIN(MIN)+ VOUT + VD

Conversely, the minimum duty cycle (DMIN) occurs when

the converter operates at the maximum input voltage:

DMIN =

VOUT + VD

VIN(MAX)+ VOUT + VD

Be sure to check that DMAX and DMIN obey:

DMAX < 1-Minimum Off-Time(MAX) • fOSC(MAX)

and

DMIN > Minimum On-Time(MAX) • fOSC(MAX)

where Minimum Off-Time, Minimum On-Time and fOSC

are specified in the Electrical Characteristics table.

SEPIC Converter: The Maximum Output Current

Capability and Inductor Selection

As shown in Figure 5, the SEPIC converter contains two

inductors:L1andL2.L1andL2canbeindependent,butcan

Figure 5. LT8330 Configured in a SEPIC Topology

VOUT

VIN

FBX

GND

EN/UVLO

LT8330

VIN

VCC

INT

CIN

COUT

CDC

8330 F05

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