Diodes PAM2401 - Manual (Page 5)

PAM2401
Document number: DS37285 Rev. 1 - 2
5 of 10
www.diodes.com
May 2014
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PAM2401
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T
A Product Line of
Diodes Incorporated
Application Information
Output Voltage Set Equation
The output voltage of the PAM2401, V
OUT
, is set by an external resistor divider from VOUT to ground as shown in figure 1. The divider tap is
connected to the FB pin and the typical value of the voltage at the FB pin is 0.6V. The following equation is used to set the
V
OUT
: V
OUT
= 0.6 (1+R1/R2) For example, if output voltage of 5V is needed, with a chosen R2 value of 100kΩ ,the value of R1 can be calculated
according to the equation, so a 750kΩ resistor should be chosen for R1.
Inductor Selection
To select an inductor for use in PAM2401 applications, it is worth noting that the inductor current saturation rating should be larger than the
possible peak inductor current to ensure proper operation, and should have low DCR (DC resistance). Using an inductor the saturation current of
which is lower than required can cause a dramatic drop in the inductance and can decay the maximum output current levels severely. For most
applications, the value of the inductor should be in the range ofs 1µH to 4.7µH. Its value is chosen based on the desired ripple current.
Larger value inductors result in lower ripple currents, and smaller value inductors result in higher ripple currents. A 1.5µH or 2.2µH inductor will be
the best choice for most PAM2401 applications. The following equation can also help give a good approximate value for the inductor.
Δ
=
ILxf
V INxD
L
D Duty Cycle=1-V
IN
/V
OUT
, F Switching Frequency = 1.0MHz, ∆IL Ripple Current in the Inductor, i.e., 20% to 40% of the maximum inductor current
(Ip).
Output and Input Capacitor Selection
Input Capacitor
At least a 10µF input capacitor is recommended to reduce the input ripple and switching noise for normal operating conditions, while a 10-22µF
capacitor may be required for higher power and dynamic loads. Larger values 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 IC.
Output Capacitor
A minimum output capacitor value of 22µF is recommended and may be increase to a larger value. The ESR of the output capacitor is important
because it determines the peak to peak output voltage ripple by the following equation:
xRESR IL V OUT Δ >> Δ 2
Multilayer ceramic capacitors are an excellent choice as they have extremely low ESR and are available in small footprints.