Datasheet LT8410, LT8410-1 (Analog Devices) - 8

LT8410/LT8410-1
OPERATION
The LT8410 series utilizes a variable peak current, variable the circuit, special precautions are taken to ensure that off-time control scheme to provide high efficiency over a the inductor current remains under control wide output current range. The LT8410 series also has a PMOS output disconnect The operation of the part can be better understood by switch. The PMOS switch is turned on when the part is referring to the Block Diagram. The part senses the output enabled via the SHDN pin. When the part is in shutdown, voltage by monitoring the internal FB node, and servoing the PMOS switch turns off, allowing the VOUT node to the FB node voltage to be equal to the FBP pin voltage. go to ground. This type of disconnect function is often The chip integrates an accurate high value resistor divider required in power supplies. (12.4M/0.4M) from the VOUT pin. The output voltage is set The differences between the LT8410 and LT8410-1 are by the FBP pin voltage, which in turn is set by an external the SW current limit and the output disconnect PMOS resistor divider from the VREF pin. The FBP pin voltage can current limit. For the LT8410, the SW current limit and also be directly biased with an external reference, allowing PMOS current limit are approximately 25mA and 19mA, full control of the output voltage during operation. respectively, while those of the LT8410-1 are approximately The switch control block senses the output of the ampli- 8mA and 4mA, respectively. fier and adjusts the switching frequency as well as other parameters to achieve regulation. During the start-up of
APPLICATIONS INFORMATION Inductor Selection Table 1. Recommended Inductors for LT8410/ LT8410-1
Several inductors that work well with the LT8410 and
L DCR SIZE PART (µH) (Ω) (mm) VENDOR
LT8410-1 are listed in Table 1. The tables are not complete, LQH2MCN680K02 68 6.6 2.0 × 1.6 × 0.9 Murata and there are many other manufacturers and devices that LQH32CN101K53 100 3.5 3.2 × 2.5 × 2.0 www.murata.com can be used. Consult each manufacturer for more detailed DO2010-683ML 68 8.8 2.0 × 2.0 × 1.0 Coilcraft information and for their entire selection of related parts, LPS3015-104ML 100 3.4 3.0 × 3.0 × 1.4 www.coilcraft.com as many different sizes and shapes are available. LPS3015-154ML 150 6.1 3.0 × 3.0 × 1.4 LPS3314-154ML 150 4.1 3.3 × 3.3 × 1.3 Inductors with a value of 47μH or higher are recommended for most LT8410 series designs. Inductors with low core
Capacitor Selection
losses and small DCR (copper wire resistance) are good The small size and low ESR of ceramic capacitors make choices for LT8410 series applications. For full output them suitable for most LT8410 applications. X5R and power, the inductor should have a saturation current rating X7R types are recommended because they retain their higher than the peak inductor current. The peak inductor capacitance over wider voltage and temperature ranges current can be calculated as: than other types such as Y5V or Z5U. A 2.2μF or higher input capacitor, and a 0.1μF to 1μF output capacitor, are VIN • 150 • 10–6 sufficient for most applications. Always use a capacitor I mA PK = ILIMIT + L with a sufficient voltage rating. Many ceramic capacitors where the worst case ILIMIT is 30mA and 10mA for LT8410 rated at 0.1μF to 1μF have greatly reduced capacitance and LT8410-1, respectively. L is the inductance value in when bias voltages are applied. Be sure to check actual henrys and VIN is the input voltage to the boost circuit. capacitance at the desired output voltage. Generally, a 0603 84101fc 8 For more information www.linear.com/LT8410 Document Outline Description Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Features Pin Functions Block Diagram Operation Applications Information Typical Applications Package Description Revision History Typical Application Related Parts