ISL6415 Просмотр технического описания (PDF) - Renesas Electronics

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ISL6415

Triple Output Regulator with Single Synchronous Buck and Dual LDO

Renesas Electronics 

ISL6415

Applications Information

LDO Regulator Capacitor Selection and Regulator

Stability

Capacitors are required at the ISL6415 LDO Regulators’

input and output for stable operation over the entire load

range and the full temperature range. Use >1µF capacitor at

the input of LDO Regulators, VIN_LDO pins. The input

capacitor lowers the source impedance of the input supply.

Larger capacitor values and lower ESR provides better

PSRR and line transient response. The input capacitor must

be located at a distance of not more then 0.5 inches from the

VIN pins of the IC and returned to a clean analog ground.

Any good quality ceramic capacitor can be used as an input

capacitor.

The output capacitor must meet the requirements of a

minimum amount of capacitance and ESR for both LDO’s.

The ISL6415 is specifically designed to work with small

ceramic output capacitors. The output capacitor’s ESR

affects stability and output noise. Use an output capacitor

with an ESR of 50m or less to insure stability and optimum

transient response. For stable operation, a ceramic

capacitor, with a minimum value of 3.3µF, is recommended

for VOUT1 for 300mA output current, and 3.3µF is

recommended for VOUT2 at 200mA load current. There is no

upper limit to the output capacitor value. Larger capacitor

can reduce noise and improve load transient response,

stability and PSRR. Higher value of output capacitor (10µF)

is recommended for LDO2 when used to power VCO

circuitry in wireless chipsets. The output capacitor should be

located very close to Vout pins to minimize impact of PC

board inductances and the other end of the capacitor should

be returned to a clean analog ground.

PWM Regulator Component Selection

INDUCTOR SELECTION

A 10µH minimum output inductor is used with the ISL6415

PWM section. Values larger then 15µH or less then 10µH

may cause stability problems because of the internal

compensation of the regulator. The important parameters of

the inductor that need to be considered are the current rating

of the inductor and the DC resistance of the inductor. The dc

resistance of the inductor will influence directly the efficiency

of the converter. Therefore, an inductor with lowest dc

resistance should be selected for highest efficiency.

In order to avoid saturation of the inductor, the inductor

should be rated at least for the maximum output current plus

the inductor ripple current.

TABLE 1. RECOMMENDED INDUCTORS

OUTPUT INDUCTOR

CURRENT VALUE

VENDOR PART #

COMMENTS

0mA to

600mA

10H

Coilcraft DO3316P-103

Coilcraft DT3316P-103

Sumida CDR63B-100

Sumida CDRH5D28-100

High

Efficiency

Coilcraft DO1608C-100 Smallest

Sumida CDRH4D28-100 Solution

0mA to

300mA

10H

Coilcraft DS1608C-103 High

Efficiency

Murata LQH4C100K04 Smallest

Solution

Output Capacitor Selection

For best performance, a low ESR output capacitor is

needed. If an output capacitor is selected with an ESR value

120m, its RMS ripple current rating will always meet the

application requirements. The RMS ripple current is

calculated as:

IRMSCO

=

VO



-1---L-–-----V---V----f--O---I--



-------1---------

2 3

The overall output ripple voltage is the sum of the voltage

spike caused by the output capacitor ESR plus the voltage

ripple caused by charge and discharging the output

capacitor:

VO

=

VO











1----L-–-----V---V----f--O---I--











-8---------C--1---O----------f

+

E

S

R





Where the highest output voltage ripple occurs at the highest

input voltage VI.

TABLE 2. RECOMMENDED CAPACITORS

CAPACITOR

VALUE ESR/m VENDOR PART #

10F

50 Taiyo Yuden

JMK316BJ106KL

COMMENTS

Ceramic

47F

68F

100 Sanyo 6TPA47M

POSCAP

100 Sprague

Tantalum

594D686X0010C2T

FN9145 Rev 0.00

Dec 27, 2004

Page 11 of 13

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