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LT8410

Ultralow Power Boost Converter with Output Disconnect

Linear Technology 

LT8410/LT8410-1

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 VOUT pin. The output voltage is set

by the FBP pin voltage, which in turn is set by an external

resistor divider from the VREF 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 amplifier

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 VOUT 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:

IPK

= ILIMIT

+

VIN

• 150 • 10–6

L

mA

where the worst case ILIMIT is 30mA and 10mA for LT8410

and LT8410-1 respectively. L is the inductance value in

Henrys and VIN is the input voltage to the boost circuit.

Table 1. Recommended Inductors for LT8410/-1

PART

L DCR

(μH) (Ω)

SIZE

(mm)

VENDOR

LQH2MCN680K02 68 6.6 2.0 × 1.6 × 0.9 Murata

LQH32CN101K53 100 3.5 3.2 × 2.5 × 2.0 www.murata.com

DO2010-683ML 68 8.8 2.0 × 2.0 × 1.0 Coilcraft

LPS3015-104ML 100 3.4 3.0 × 3.0 × 1.4 www.coilcraft.com

LPS3015-154ML 150 6.1 3.0 × 3.0 × 1.4

LPS3314-154ML 150 4.1 3.3 × 3.3 × 1.3

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

84101f

8

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