LT8580EDD-TRPBF Ver la hoja de datos (PDF) - Linear Technology

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componentes Descripción

Fabricante

LT8580EDD-TRPBF

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

Linear Technology 

LT8580

Applications Information

Dual Inductor Inverting Converter Component

Selection (Coupled or UnCoupled Inductors)

VIN

5V TO 40V

L1

• 22µH

C1

1µF

10k

VIN

SW

SHDN

FBX

CIN

4.7µF

LT8580

SYNC

VC

RT GND SS

RT

113k

CSS

0.22µF

L2

22µH •

D1

RFBX

182k

VOUT

–15V

90mA (VIN = 5V)

210mA (VIN = 12V)

420mA (VIN = 40V)

COUT

4.7µF

RC

13.7k

CC

10nF

CF

47pF

8580 F17

Figure 17. Dual Inductor Inverting Converter: The Component

Values and Voltages Given Are Typical Values for a 750kHz

Wide Input (5V to 40V) to –15V Inverting Topology Using

Coupled Inductors

Due to its unique FBX pin, the LT8580 can work in a dual

inductor inverting configuration as in Figure 17. Chang-

ing the connections of L2 and the Schottky diode in the

SEPIC topology results in generating negative output

voltages. This solution results in very low output voltage

ripple due to inductor L2 being in series with the output.

Output disconnect is inherently built into this topology

due to the capacitor C1.

Table 6 is a step-by-step set of equations to calculate

component values for the LT8580 when operating as a

dual inductor inverting 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 6.

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

Table 6. Dual Inductor Inverting 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–

0.4 V

DCMIN

=

VIN(M AX )

VOUT + 0.5 V

+ VOUT + 0.5 V–

0.4 V

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)

LMAX

=

(VIN(MIN) – 0.4V) • DCMAX

fOSC • 0.08 A

(3)

Step 4:

IRIPPLE

Step 5:

IOUT

• 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

Step 6:

D1

Step 7:

C1

Step 8:

COUT

( ) IOUT(MAX)

=

⎛

⎜1A

−

IRIPPLE(MAX

)

⎞

⎟

•

⎝

2⎠

1− DCMIN

VR > VIN + |VOUT|; IAVG > IOUT

C1 ≥ 1µF; VRATING ≥ VIN(MAX) + |VOUT|

COUT

≥

8

•

IRIPPLE(M AX )

fOSC (0.005 • VOUT

)

Step 9:

CIN

CIN ≥ CVIN + CPWR ≥

1A • DCMAX

+

IRIPPLE(M AX )

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

Step 10:

RFBX

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

RFBX

=

VOUT + 3mV

83.3µA

Step 11:

RT

R

T

=

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

24

For more information www.linear.com/LT8580

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