LT8580 Ver la hoja de datos (PDF) - Linear Technology

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componentes Descripción

Fabricante

LT8580

Boost/SEPIC/Inverting DC/DC Converter with 1A, 65V Switch, Soft-Start and Synchronization

Linear Technology 

LT8580

Applications Information

SEPIC Converter Component Selection

(Coupled or UnCoupled Inductors)

VIN

L1

• 22µH

C1

1µF

D1

9V TO 16V

487k

L2

22µH

VOUT

12V

240mA

CIN

4.7µF

VIN

SW

SHDN

FBX

LT8580

• RFBX

130k

SYNC

VC

RT GND SS

RC

16.2k

RT

84.5k

CSS

CC

0.22µF

1nF

COUT

4.7µF

CF

22pF

8580 F16

Figure 16. SEPIC Converter: The Component Values and Voltages

Given Are Typical Values for a 1MHz, 9V to 16V Input to 12V

Output SEPIC Converter

The LT8580 can also be configured as a SEPIC, as shown

in Figure 16. This topology allows for positive output volt-

ages that are lower, equal or higher than the input volt-

age. Output disconnect is inherently built into the SEPIC

topology, meaning no DC path exists between the input

and output due to capacitor C1.

Table 5. SEPIC Design Equations

PARAMETERS/EQUATIONS

Step 1: Pick VIN, VOUT and fOSC to calculate equations below

Inputs

Step 2:

DC

DCMAX

=

VIN(MIN)

VOUT + 0.5 V

+ VOUT + 0.5 V– 0.4V

DCMIN

=

VIN(M AX )

VOUT + 0.5 V

+ VOUT + 0.5 V– 0.4V

Step 3:

L

LTYP

=

(VIN(MIN) – 0.4V) • DCMAX

fOSC • 0.3A

(1)

LMIN

=

1.25

•

(VIN(MIN) – 0.4V) • (2 • DCMAX

(DCMAX − 300nS • fOSC ) • fOSC •

– 1)

(1–

DCMAX

)

(2)

Step 4:

IRIPPLE

Step 5:

IOUT

LMAX

=

(VIN(MIN) – 0.4V) • DCMAX

fOSC • 0.08 A

(3)

• Solve equations 1, 2 and 3 for a range of L values

• The minimum of the L value range is the higher of LTYP and LMIN

• The maximum of the L value range is LMAX

• L = L1 = L2 for coupled inductors

• L = L1|| L2 for uncoupled inductors

IRIPPLE(MIN)

=

(VIN(MIN)

– 0.4V)

fOSC • L

•

DCMAX

IRIPPLE(M AX )

=

(VIN(MAX) – 0.4V)

fOSC • L

• DCMIN

( ) IOUT(MIN)

=

⎛

⎜1A

−

IRIPPLE(MIN)

⎞

⎟

•

⎝

2⎠

1− DCMAX

Table 5 is a step-by-step set of equations to calculate com-

ponent values for the LT8580 when operating as a SEPIC

converter. Input parameters are input and output voltage,

and switching frequency (VIN, VOUT and fOSC, respectively).

Refer to the Applications Information section for further

information on the design equations presented in Table 5.

Variable Definitions:

VIN = Input Voltage

VOUT = Output Voltage

Step 6:

D1

Step 7:

C1

Step 8:

COUT

Step 9:

CIN

( ) IOUT(MAX)

=

⎛

⎜1A

−

IRIPPLE(MAX

)

⎞

⎟

•

⎝

2⎠

1− DCMIN

VR > VIN + VOUT; IAVG > IOUT

C1 ≥ 1µF; VRATING ≥ VIN

COUT

≥

IOUT(MIN) • DCMAX

fOSC • 0.005 • VOUT

CIN ≥ CVIN + CPWR ≥

1A • DCMAX

+

IRIPPLE(M AX )

40 • fOSC • 0.005 • VIN(MIN) 8 • fOSC • 0.005 • VIN(MAX)

DC = Power Switch Duty Cycle

fOSC = Switching Frequency

IOUT = Maximum Average Output Current

IRIPPLE = Inductor Ripple Current

Step 10:

RFBX

• Refer to the Capacitor Selection Section for definition of CVIN and CPWR

RFBX

=

VOUT − 1.204V

83.3µA

Step 11:

RT

RT

= 85.5

fOSC

–1 ;

fOSC

in MHz and RT

in kΩ

Note 1: This table uses 1A for the peak switch current. Refer to the

Electrical Characteristics Table and Typical Performance Characteristics

plots for the peak switch current at an operating duty cycle.

Note 2: The final values for COUT, CIN and C1 may deviate from the

previous equations in order to obtain desired load transient performance.

8580f

For more information www.linear.com/LT8580

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