LT3579IUFD-1-PBF(RevA) 查看數據表（PDF） - Linear Technology

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LT3579IUFD-1-PBF
(Rev.:RevA)

6A Boost/Inverting DC/DC Converter with Fault Protection

Linear Technology 

LT3579/LT3579-1

APPLICATIONS INFORMATION

DUAL INDUCTOR INVERTING CONVERTER COMPONENT

SELECTION – COUPLED OR UN-COUPLED INDUCTORS

L1

3.3µH

C1

4.7µF

VIN

5V

SW1 SW2

VIN

FB

CIN

SHDN

GATE

22µF 100k

LT3579

L2

3.3µH

D1

30V, 2A

RFB

144k

VOUT

–12V

1.2A

COUT

10µF

×2

FAULT

CLKOUT

RT

VC

SYNC GND SS

RC

CF

20k

RT

CSS

27pF

CC

72k

0.22µF

1nF

35791 F08

Figure 8. Dual Inductor Inverting Converter – The Component

Values Given Are Typical Values for a 1.2MHz, 5V to –12V Inverting

Topology Using Coupled Inductors

Due to its unique FB pin, the LT3579 can work in a Dual

Inductor Inverting configuration as in Figure 8. Changing

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 in series with the output. Output

disconnect is inherently built into this topology due to the

capacitor C1.

Table 3 is a step-by-step set of equations to calculate

component values for the LT3579 when operating as a Dual

Inductor Inverting converter using coupled inductors. Input

parameters are input and output voltage, and switching

frequency (VIN, VOUT and fOSC respectively). Refer to the

Appendix for further information on the design equations

presented in Table 3.

Variable Definitions:

VIN = Input Voltage

VOUT = Output Voltage

DC = Power Switch Duty Cycle

fOSC = Switching Frequency

IOUT = Maximum Output Current

IRIPPLE = Inductor Ripple Current

Table 3. Dual Inductor Inverting Design Equations

PARAMETERS/EQUATIONS

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

Step 2: DC

DC ≅

| VOUT | + 0.5V

VIN + | VOUT | +0.5V – 0.27V

Step 3: L

( ) LTYP =

VIN – 0.27V • DC

fOSC • 1.8A

(1)

LMIN

=

(VIN – 0.27V) • (2 • DC –

4A • fOSC • (1 – DC)

1)

(2)

( ) LMAX =

VIN – 0.27V • DC

fOSC • 0.5A

(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.

Step 4: IRIPPLE

( ) IRIPPLE =

VIN – 0.27V • DC

fOSC • L

Step 5: IOUT

( ) IOUT

=





6A

–

IRIPPLE

2





•

1 – DC

Step 6: D1

VR > VIN +| VOUT | ; IAVG > IOUT

Step 7: C1

4.7µF (typical) ; VRATING > VIN + | VOUT |

Step 8: COUT

COUT

=

8

•

fOSC

IRIPPLE

• 0.005

• | VOUT

|

Step 9: CIN

CIN = CPWR + CVIN

CIN

=

8

•

IRIPPLE

fOSC • 0.005 •

VIN

+

40

•

6A • DC

fOSC • 0.005 •

VIN

Step 10: RFB

RFB

=

| VOUT | + 9mV

83.3µA

Step 11: RT

RT

=

87.6

fOSC

– 1;

fOSC

in MHz

and RT

in kΩ

Note: The maximum design target for peak switch current is 6A and

is used in this table. The final values for COUT and CIN may deviate

from the above equations in order to obtain desired load transient

performance for a particular application.

For more information www.linear.com/LT3579

35791fa

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