LT8331 datasheet(19/30 Pages) AD

19 / 30 page

LT8365

Rev. A

For more information www.analog.com

It is recommended that the peak repetitive reverse voltage

rating VRRM is higher than VOUT + VIN(MAX) by a safety

margin (a 10V safety margin is usually sufficient).

The power dissipated by the diode is:

PD = IO(MAX) • VD

where VD is diode’s forward voltage drop, and the diode

junction temperature is:

TJ = TA + PD • RθJA

The RθJA used in this equation normally includes the RθJC

for the device, plus the thermal resistance from the board,

to the ambient temperature in the enclosure. TJ must not

exceed the diode maximum junction temperature rating.

SEPIC Converter: Output and Input Capacitor Selection

The selections of the output and input capacitors of the

SEPICconverteraresimilartothoseoftheboostconverter.

SEPIC Converter: Selecting the DC Coupling Capacitor

The DC voltage rating of the DC coupling capacitor (CDC,

as shown in Figure 6) should be larger than the maximum

input voltage:

VCDC > VIN(MAX)

CDC has nearly a rectangular current waveform. During the

switchoff-time,thecurrentthroughCDCisIIN,whileapproxi-

mately –IO flows during the on-time. The RMS rating of the

coupling capacitor is determined by the following equation:

IRMS(CDC) > IO(MAX) •

VOUT + VD

VIN(MIN)

A low ESR and ESL, X5R or X7R ceramic capacitor works

well for CDC.

INVERTING CONVERTER APPLICATIONS

The LT8365 can be configured as a dual-inductor inverting

topology, as shown in Figure 8. The VOUT to VIN ratio is:

VOUT + VD

VIN

1 − D

in continuous conduction mode (CCM).

Inverting Converter: Switch Duty Cycle and Frequency

For an inverting converter operating in CCM, the duty

cycle of the main switch can be calculated based on the

negative output voltage (VOUT)andtheinputvoltage(VIN).

Themaximumdutycycle(DMAX)occurswhentheconverter

has the minimum input voltage:

DMAX =

VOUT + VD

VOUT + VD + VIN(MIN)

Conversely, the minimum duty cycle (DMIN) occurs when

the converter operates at the maximum input voltage :

DMIN =

VOUT + VD

VOUT + VD + VIN(MAX)

Be sure to check that DMAX and DMIN obey :

DMAX < 1 – Minimum Off-Time(MAX) • fOSC(MAX)

and

DMIN > Minimum On-Time(MAX) • fOSC(MAX)

where Minimum Off-Time, Minimum On-Time and fOSC

are specified in the Electrical Characteristics table.

Inverting Converter: Inductor, Output Diode and Input

Capacitor Selections

The selections of the inductor, output diode and input

capacitor of an inverting converter are similar to those of

the SEPIC converter. Please refer to the corresponding

SEPIC Converter sections.

APPLICATIONS INFORMATION

Figure 8. A Simplified Inverting Converter

CDC

VIN

CIN

COUT

VOUT

8365 F10

GND

LT8365

–

+ –

LT8331 датащи(PDF) 19 Page - Analog Devices

LT8331 датащи(HTML) 19 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

датащи скачать

ссылки URL