LTC7130 datasheet(20/36 Pages) LINER

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LTC7130

7130fb

For more information www.linear.com/LTC7130

Tables 1 and 2 provide heat sink and thermal conductive

adhesive tape information.

Table 1. Heat Sink Manufacturer (Thermally Conductive

Adhesive Tape Pre-Attached)

HEAT SINK

MANUFACTURER

PART NUMBER

WEBSITE

Cool Innovations

3-040404U

www.coolinnovations.com

Table 2. Thermally Conductive Adhesive Tape Vendor

THERMALLY CONDUCTIVE

ADHESIVE TAPE

MANUFACTURER

PART NUMBER WEBSITE

Chomerics

T411

www.chomerics.com

Inductor Value Calculation

Given the desired input and output voltages, the inductor

value and operating frequency, fOSC, directly determine

the inductor’s peak-to-peak ripple current:

IRIPPLE =

VOUT

VIN

VIN – VOUT

fOSC •L

⎛

⎝

⎜

⎞

⎠

⎟

Lower ripple current reduces core losses in the inductor,

ESR losses in the output capacitors, and output voltage

ripple. Thus, highest efficiency operation is obtained at

low frequency with a small ripple current. Achieving this,

however, requires a large inductor.

It is recommended to choose a ripple current that is about

50% of IOUT(MAX). Note that the largest ripple current oc-

curs at the highest input voltage. To guarantee that ripple

currentdoesnotexceedaspecifiedmaximum,theinductor

should be chosen according to:

L ≈

VIN – VOUT

fOSC •IRIPPLE

•

VOUT

VIN

Inductor Core Selection

Once the inductance value is determined, the type of in-

ductor must be selected. Core loss is independent of core

size for a fixed inductor value, but it is very dependent on

inductance selected. As inductance increases, core losses

go down. Unfortunately, increased inductance requires

moreturnsofwireandthereforecopperlosseswillincrease.

Ferrite designs have very low core loss and are preferred

at high switching frequencies, so design goals can con-

centrate on copper loss and preventing saturation. Ferrite

core material saturates “hard,” which means that induc-

tance collapses abruptly when the peak design current is

exceeded. This results in an abrupt increase in inductor

ripple current and consequent output voltage ripple. Do

not allow the core to saturate!

CIN and COUT Selection

Incontinuousmode,thesourcecurrentofthetopMOSFET

is a square wave of duty cycle (VOUT)/(VIN). To prevent

large voltage transients, a low ESR capacitor sized for the

APPLICATIONS INFORMATION

Figure 8. Temperature Derating Curve Based on the

DC2341A Demo Board

Figure 9. Temperature Derating Curve Based on the

DC2341A Demo Board

VOUT = 1.5V

VIN = 12V

fSW = 500kHz

DC2341A DEMO BOARD

WITH HEAT SINK

0LFM

200LFM

400LFM

AMBIENT TEMPERATURE (°C)

100

125

Thermal Derating VIN = 12V

7130 F08

VOUT = 1.5V

fSW = 500kHz

DC2341A DEMO BOARD

WITH HEAT SINK

0LFM

200LFM

400LFM

AMBIENT TEMPERATURE (°C)

100

125

Thermal Derating VIN = 20V

7130 F09

VIN = 20V

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