LT8580 데이터 시트보기 (PDF) - Linear Technology

부품명

상세내역

제조사

LT8580

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

Linear Technology 

LT8580

Applications Information

Boost Converter Component Selection

Table 4. Boost Design Equations

PARAMETERS/EQUATIONS

L1

15µH

D1

VIN

5V

10k

VIN

SW

RFBX

VOUT

12V

200mA

Step 1:

Inputs

Step 2:

DC

Pick VIN, VOUT, and fOSC to calculate equations below

DCMAX

=

VOUT – VIN(MIN) + 0.5 V

VOUT + 0.5 V– 0.4 V

CIN

2.2µF

SHDN

FBX

LT8580

SYNC

VC

RT GND SS

130k

RC

6.04k

CF

COUT

4.7µF

Step 3:

L1

DCMIN

=

VOUT – VIN(MAX)

VOUT + 0.5 V–

+ 0.5 V

0.4 V

LTYP

=

(VIN(MIN) – 0.4V) • DCMAX

fOSC • 0.3A

(1)

RT

56.2k

CSS

0.22µF

CC

3.3nF

47pF

8580 F15

LMIN

=

1.25

(VIN(MIN)

• (DCMAX

– 0.4V) • (2 • DCMAX – 1)

− 300nS • fOSC ) • (1– DCMAX

)

(2)

Figure 15. Boost Converter: The Component Values and Voltages

Given Are Typical Values for a 1.5MHz, 5V to 12V Boost

The LT8580 can be configured as a boost converter as in

Figure 15. This topology allows for positive output voltages

that are higher than the input voltage. A single feedback

resistor sets the output voltage. For output voltages higher

than 60V, see the Charge Pump Aided Regulators section.

Table 4 is a step-by-step set of equations to calculate com-

ponent values for the LT8580 when operating as a boost

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 4.

Variable Definitions:

VIN = Input Voltage

VOUT = Output Voltage

DC = Power Switch Duty Cycle

fOSC = Switching Frequency

IOUT = Maximum Average Output Current

IRIPPLE = Inductor Ripple Current

LMAX1

=

(VIN(MIN) – 0.4V) • DCMAX

fOSC • 0.08 A

(3)

LMAX2

=

(VIN(MAX) –

fOSC

0.4V) • DCMIN

• 0.08A

(4)

Step 4:

IRIPPLE

Step 5:

IOUT

• Solve equations 1 to 4 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 the lower of LMAX1 and LMAX2.

IRIPPLE(MIN)

=

(VIN(MIN)

– 0.4V) •

fOSC • L1

DCMAX

IRIPPLE(M AX )

=

(VIN(MAX) – 0.4V)

fOSC • L1

•

DCMIN

IOUT(MIN)

=

⎛

⎜1A

⎝

−

IRIPPLE(MIN)

2

⎞

⎟

⎠

•

(1−

DCMAX

)

IOUT(MAX

)

=

⎛

⎜1A

⎝

−

IRIPPLE(M AX )

2

⎞

⎟

⎠

•

(1−

DCMIN

)

Step 6:

D1

Step 7:

COUT

Step 8:

CIN

VR > VOUT; IAVG > IOUT

COUT

≥

IOUT • 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)

Step 9:

RFBX

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

RFBX

=

VOUT − 1.204V

83.3µA

Step

10:

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 and CIN may deviate from the previous

equations in order to obtain desired load transient performance.

8580f

22

For more information www.linear.com/LT8580

Share Link: