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L +

VBAT

(VOUT * VBAT)

DIL

ƒ

VOUT

(4)

Capacitor Selection

Input Capacitor

Output Capacitor

C

min +

I

O

VOUT * VBAT

ƒ

DV

VOUT

(5)

DVESR + IO

R

ESR

(6)

TPS61070, TPS61071

TPS61072, TPS61073

SLVS510A – JULY 2006 – REVISED JANUARY 2007

The second parameter for choosing the inductor is the desired current ripple in the inductor. Normally, it is

advisable to work with a ripple of less than 20% of the average inductor current. A smaller ripple reduces the

magnetic hysteresis losses in the inductor, as well as output voltage ripple and EMI. But in the same way,

regulation time rises at load changes. In addition, a larger inductor increases the total system costs. With these

parameters, it is possible to calculate the value for the inductor by using Equation 4:

Parameter f is the switching frequency and

∆I

the desired inductor has the value of 4 µH. With this calculated value and the calculated currents, it is possible

to choose a suitable inductor. In typical applications, a 4.7 µH inductance is recommended. The device has

been optimized to operate with inductance values between 2.2 µH and 10 µH. Nevertheless, operation with

higher inductance values may be possible in some applications. Detailed stability analysis is then recommended.

Care must be taken because load transients and losses in the circuit can lead to higher currents as estimated in

Equation 4. Also, the losses in the inductor caused by magnetic hysteresis losses and copper losses are a major

parameter for total circuit efficiency.

The following inductor series from different suppliers have been used with the TPS6107x converters:

Table 1. List of Inductors

VENDOR

INDUCTOR SERIES

VLF3010

TDK

VLF4012

744031xxx

Wurth Elektronik

744042xxx

EPCOS

B82462-G4

SD18

Cooper Electronics Technologies

SD20

CB2016B xxx

Taiyo Yuden

CB2518B xxx

At least a 10 µF input capacitor is recommended to improve transient behavior of the regulator and EMI

behavior of the total power supply circuit. A ceramic capacitor or a tantalum capacitor with a 100-nF ceramic

capacitor in parallel, placed close to the IC, is recommended.

The major parameter necessary to define the output capacitor is the maximum allowed output voltage ripple of

the converter. This ripple is determined by two parameters of the capacitor, the capacitance and the ESR. It is

possible to calculate the minimum capacitance needed for the defined ripple, supposing that the ESR is zero, by

using Equation 5:

Parameter f is the switching frequency and

∆V is the maximum allowed ripple.

With a chosen ripple voltage of 10 mV, a minimum capacitance of 4.5 µF is needed. In this value range, ceramic

capacitors are a good choice. The ESR and the additional ripple created are negligible. It could be calculated

using Equation 6:

15

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