LP8862-Q1

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SNVSA75A – NOVEMBER 2015 – REVISED NOVEMBER 2015

approach is to choose an inductor that has a saturation current rating greater than the maximum current limit. A

saturation current rating of at least 3 A is recommended for most applications. See Table 3 for inductance

recommendations for the different switching frequency ranges. Resistance of the inductor must be less than 300

m

Ω for good efficiency.

See detailed information in Understanding Boost Power Stages in Switch Mode Power Supplies. “Power Stage

Designer™ Tools” can be used for the boost calculation: http://www.ti.com/tool/powerstage-designer.

8.2.1.2.2

Output Capacitor Selection

DC-bias effect can reduce the effective capacitance by up to 80%, which needs to be considered in capacitance

value selection. Capacitance recommendations for different boost switching frequencies are shown in Table 3.

To minimize audible noise of ceramic capacitors their geometric size must typically be minimized.

8.2.1.2.3

Input Capacitor Selection

bias effect can reduce the effective capacitance by up to 80%, which needs to be considered in capacitance

value selection. Capacitance recommendations for different boost switching frequencies are shown in Table 3.

8.2.1.2.4

LDO Output Capacitor

A ceramic capacitor with at least 10-V voltage rating is recommended for the output capacitor of the LDO. The

DC-bias effect can reduce the effective capacitance by up to 80%, which needs to be considered in capacitance

value selection. Typically a 1-µF capacitor is sufficient.

8.2.1.2.5

Diode

A Schottky diode should be used for the boost output diode. Do not use ordinary rectifier diodes, since slow

switching speeds and long recovery times cause the efficiency and the load regulation to suffer. Diode rating for

peak repetitive current should be greater than inductor peak current (up to 3 A) to ensure reliable operation.

Average current rating must be greater than the maximum output current. Schottky diodes with a low forward

drop and fast switching speeds are ideal for increasing efficiency. Choose a reverse breakdown voltage of the

Schottky diode significantly larger than the output voltage.

8.2.1.2.6

Power Line Transistor

Current rating for the FET must be the same as input peak current or greater. Transfer characteristic is very

source is sufficient.

8.2.1.2.7

Input Current Sense Resistor

A high-power 50 m

Ω resistor must be used for sensing the boost input current. Power rating can be calculated

proportionally.

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