PAM2841

Document number: DS36411 Rev. 2 - 2

9 of 15

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October 2017

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PAM2841

Application Information

Inductor Selection

The selection of the inductor affects steady state operation as well as transient behavior and loop stability. These factors make it the most

important component in power regulator design. There are three important inductor specifications, inductor value, DC resistance and saturation

current. Considering inductor value alone is not enough.

The inductor value determines the inductor ripple current. Choose an inductor that can handle the necessary peak current without saturation, the

inductor DC current given by:

) = efficiency.

Inductor values can have ±20% tolerance with no current bias. When the inductor current approaches saturation level, its inductance can

decrease 20% to 35% from the 0A value depending on how the inductor vendor defines saturation current. Using an inductor with a smaller

inductance value causes discontinuous PWM when the inductor current ramps down to zero before the end of each switching cycle. This reduces

the boost converter's maximum output current, causes large input voltage ripple and reduces efficiency. Large inductance value provides much

more output current and higher conversion efficiency. For these reasons, an inductor within 4.7µH to 22µH value range is recommended.

Schottky Diode Selection

The high switching frequency of the PAM2841 demands a high-speed rectification for optimum efficiency. Ensure that the diode average and peak

current rating exceeds the average output current and peak inductor current. In addition, the diode's reverse breakdown voltage must exceed the

open protection voltage.

Input and Output Capacitor Selection

Input Capacitor

At least a 1µF input capacitor is recommended to reduce the input ripple and switching noise for normal operating conditions. Larger value and

lower ESR (Equivalent Series Resistance) may be needed if the application require very low input ripple. It follows that ceramic capacitors are a

good choice for applications. Note that the input capacitor should be located as close as possible to the device.

Output Capacitor

The output capacitor is mainly selected to meet the requirement for the output ripple and loop stability. This ripple voltage is related to the

capacitor's capacitance and its equivalent series resistance (ESR). A output capacitor of 1

μF minimum is recommended and maybe need a larger

capacitor. The total output voltage ripple has two components: the capacitive ripple caused by the charging and discharging on the output

capacitor, and the ohmic ripple due to the capacitor's equivalent series resistance (ESR):

Multilayer ceramic capacitors are an excellent choice as they have extremely low ESR and are available in small footprints. Capacitance and ESR

variation with temperature should be considered for best performance in applications with wide operating temperature ranges.

Dimming Control

There are 4 different types of dimming control methods:

1.

Using an External PWM Signal to ENA Pin

With the PWM signal applied to the ENA pin, the PAM2841 is alternately turned on or off by the PWM signal. The LEDs operate at either zero or

full current. The average LED current changes proportionally with the duty cycle of the PWM signal. A 0% duty cycle turns off the PAM2841 and

leads to zero LED current. A 100% duty cycle generates full current. Also the recommend dimming frequency is between 100Hz and 200Hz.