LT8410/LT8410-1
8
84101fc
For more information www.linear.com/LT8410
OPERATION
The LT8410 series utilizes a variable peak current, variable
off-time control scheme to provide high efficiency over a
wide output current range.
The operation of the part can be better understood by
referring to the Block Diagram. The part senses the output
voltage by monitoring the internal FB node, and servoing
the FB node voltage to be equal to the FBP pin voltage.
The chip integrates an accurate high value resistor divider
(12.4M/0.4M) from the V
OUT
pin. The output voltage is set
by the FBP pin voltage, which in turn is set by an external
resistor divider from the V
REF
pin. The FBP pin voltage can
also be directly biased with an external reference, allowing
full control of the output voltage during operation.
The switch control block senses the output of the ampli-
fier and adjusts the switching frequency as well as other
parameters to achieve regulation. During the start-up of
the circuit, special precautions are taken to ensure that
the inductor current remains under control
The LT8410 series also has a PMOS output disconnect
switch. The PMOS switch is turned on when the part is
enabled via the SHDN pin. When the part is in shutdown,
the PMOS switch turns off, allowing the V
OUT
node to
go to ground. This type of disconnect function is often
required in power supplies.
The differences between the LT8410 and LT8410-1 are
the SW current limit and the output disconnect PMOS
current limit. For the LT8410, the SW current limit and
PMOS current limit are approximately 25mA and 19mA,
respectively, while those of the LT8410-1 are approximately
8mA and 4mA, respectively.
APPLICATIONS INFORMATION
Inductor Selection
Several inductors that work well with the LT8410 and
LT8410-1 are listed in Table 1. The tables are not complete,
and there are many other manufacturers and devices that
can be used. Consult each manufacturer for more detailed
information and for their entire selection of related parts,
as many different sizes and shapes are available.
Inductors with a value of 47μH or higher are recommended
for most LT8410 series designs. Inductors with low core
losses and small DCR (copper wire resistance) are good
choices for LT8410 series applications. For full output
power, the inductor should have a saturation current rating
higher than the peak inductor current. The peak inductor
current can be calculated as:
I
PK
= I
LIMIT
+
V
IN
• 150 • 10
mA
where the worst case I
LIMIT
is 30mA and 10mA for LT8410
and LT8410-1, respectively. L is the inductance value in
henrys and V
IN
is the input voltage to the boost circuit.
Table 1. Recommended Inductors for LT8410/ LT8410-1
PART
L
(µH)
DCR
(Ω)
SIZE
(mm)
VENDOR
LQH2MCN680K02
LQH32CN101K53
68
100
6.6
3.5
2.0 × 1.6 × 0.9
3.2 × 2.5 × 2.0
Murata
www.murata.com
DO2010-683ML
LPS3015-104ML
LPS3015-154ML
LPS3314-154ML
68
100
150
150
8.8
3.4
6.1
4.1
2.0 × 2.0 × 1.0
3.0 × 3.0 × 1.4
3.0 × 3.0 × 1.4
3.3 × 3.3 × 1.3
Coilcraft
www.coilcraft.com
Capacitor Selection
The small size and low ESR of ceramic capacitors make
them suitable for most LT8410 applications. X5R and
X7R types are recommended because they retain their
capacitance over wider voltage and temperature ranges
than other types such as Y5V or Z5U. A 2.2μF or higher
input capacitor, and a 0.1μF to 1μF output capacitor, are
sufficient for most applications. Always use a capacitor
with a sufficient voltage rating. Many ceramic capacitors
rated at 0.1μF to 1μF have greatly reduced capacitance
when bias voltages are applied. Be sure to check actual
capacitance at the desired output voltage. Generally, a 0603
