LT8330
13
8330fa
For more information
www.linear.com/LT8330
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
large copper layers to spread heat dissipated by the LT8330
and to further reduce the thermal resistance (
θ
JA
) values
listed in the Pin Configuration section. Power dissipation
within the LT8330 (P
DISS_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,
T
J
(LT8330) = T
A
+
θ
JA
•
P
DISS_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:
V
OUT
+
V
D
V
IN
=
D
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 (V
OUT
), the input voltage (V
IN
) and the diode
forward voltage (V
D
).
The maximum duty cycle (D
MAX
) occurs when the converter
operates at the minimum input voltage:
D
MAX
=
V
OUT
+
V
D
V
IN(MIN)
+
V
OUT
+
V
D
Conversely, the minimum duty cycle (D
MIN
) occurs when
the converter operates at the maximum input voltage:
D
MIN
=
V
OUT
+
V
D
V
IN(MAX)
+
V
OUT
+
V
D
Be sure to check that D
MAX
and D
MIN
obey:
D
MAX
< 1-Minimum Off-Time
(MAX)
•
f
OSC(MAX)
and
D
MIN
> Minimum On-Time
(MAX)
•
f
OSC(MAX)
where Minimum Off-Time, Minimum On-Time and f
OSC
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: L1 and L2. L1 and L2 can be independent, but can
Figure 5. LT8330 Configured in a SEPIC Topology
L1
L2
V
OUT
V
IN
SW
FBX
GND
EN/UVLO
LT8330
V
IN
V
CC
INT
D1
C
IN
C
OUT
C
DC
8330 F05
