IP1001 datasheet(11/18 Pages) IRF

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iP1001

DESIGNPROCEDURE

Inductor Selection

The inductor is selected according to the following

expression.

L = V

OUT x (1-D) / (fsw x ∆IL)

where, D = V

OUT

/ V

OUT is the output voltage in Volts,

fsw is the switching frequency in kHz,

∆I

L is the output inductor ripple current.

The inductor value should be selected from 0.8

µH

to 2.0

µH range.

Output Capacitor Selection

Use tantalum or POSCAP type capacitors for iP1001.

Selection of the output capacitors depends on

several factors.

• Low effective ESR for ripple and load transient

requirements.

• Stability.

To support the load transients and to stay within a

specified voltage dip

∆V due to the transients, ESR

selection should satisfy the following equation:

ESR ≤ ∆V/∆I

where,

∆I is the transient load step

If output voltage ripple is required to be maintained

at specified levels then, the following expression

should be used to select the output capacitors.

ESR ≤ Vp-p / ∆IL

where, V

p-p is the peak to peak output voltage ripple.

The value of the output capacitor ESR zero frequency

also determines stability. The value of the ESR zero

frequency is calculated by the expression:

ESR = 1 / (2π x fESR x COUT)

A 470

µF POSCAP capacitor has a maximum 35mΩ

of ESR which provides 9.7kHz zero frequency.

The ESR zero frequency must be set below 12kHz.

This value is calculated assuming the capacitor

datasheet maximum ESR value.

Example:

To determine the amount of capacitance

to meet a 30mVp-p output ripple, with 4A

inductor current ripple requirement.

The calculated ESR will be = 30mV/4A =

7.5m

Ω. This will require 5 x 470uF POSCAP

capacitors. The total ESR will result in a

9.7kHz zero frequency.

For stable operation:

• Set the resonant frequency fo of the output

inductor and capacitor between 2kHz and 4kHz.

The resonant frequency is calculated using the

following expression:

fo = 1/ (2

π x (√LC))

• Select the output inductor value between 0.8µµµµµH

to 2.0

µµµµµH and the output capacitance between

1880

µµµµµF (4x 470µµµµµF) and 5600µµµµµF (12x470µµµµµF)

• Set the minimum output ripple voltage to be

greater than 0.5% of the output voltage. Select the

capacitor by ESR and by voltage rating rather than

capacitance.

External Input Capacitor Selection

The switching currents impose RMS current

requirements on the input capacitors. The following

expression allows the selection of the input

capacitors, based on the input RMS current:

RMS = ILOAD x ( √D x (1-D))

where, D = V

OUT/VIN

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