LT3579E(RevA) データシートの表示（PDF） - Linear Technology

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LT3579E
(Rev.:RevA)

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

Linear Technology 

LT3579/LT3579-1

APPLICATIONS INFORMATION

BOOST CONVERTER COMPONENT SELECTION

VIN

5V

L1

2.2µH

D1

30V, 4A

COUT1

OPTIONAL

M1

VOUT

12V

1.7A

10µF

RFB

SW1 SW2

130k

VIN

100k

FAULT

FB

GATE

RGATE

6.3k

COUT

10µF

VIN

200k

CIN

22µF

LT3579

SHDN

CLKOUT

RT

VC

SYNC GND SS

RT

86.6k

CSS

0.1µF

CF

47pF

RC

8k

CC

2.2nF

35791 F06

Figure 6. Boost Converter – The Component Values Given Are

Typical Values for a 1MHz, 5V to 12V Boost

The LT3579 can be configured as a Boost converter as in

Figure 6. This topology allows for positive output voltages

that are higher than the input voltage. An external PMOS

(optional) driven by the GATE pin of the LT3579 can achieve

input or output disconnect during a FAULT event. A single

feedback resistor sets the output voltage. For output

voltages higher than 40V, see the Charge Pump topology

in the Charge Pump Aided Regulators section.

Table 1 is a step-by-step set of equations to calculate

component values for the LT3579 when operating as a

Boost converter. 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 1.

Variable Definitions:

VIN = Input Voltage

VOUT = Output Voltage

DC = Power Switch Duty Cycle

fOSC = Switching Frequency

IOUT = Maximum Output Current

IRIPPLE = Inductor Ripple Current

RDSON_PMOS = RDSON of External PMOS (set to 0 if not

using PMOS)

Table 1. Boost Design Equations

PARAMETERS/EQUATIONS

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

Inputs

Step 2:

DC

DC ≅ VOUT – VIN + 0.5V

VOUT + 0.5V – 0.27V

Step 3:

L1

Step 4:

IRIPPLE

( ) 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 L1 values.

• The minimum of the L1 value range is the higher of LTYP

and LMIN.

• The maximum of the L1 value range is LMAX.

( ) IRIPPLE =

VIN – 0.27V • DC

fOSC • L1

Step 5:

IOUT

( ) IOUT

=





6A

–

IRIPPLE

2





•

1 – DC

Step 6:

D1

VR > VOUT ; IAVG > IOUT

Step 7:

COUT,

COUT1

( ) COUT =COUT1 = fOSC •

IOUT • DC

0.01•VOUT –0.5•IOUT

• RDSON_PMOS

Step 8:

CIN

Step 9:

RFB

CIN = CPWR + CVIN

CIN

=

8

•

IRIPPLE

fOSC • 0.005

•

VIN

+

40

•

6A • DC

fOSC • 0.005

•

VIN

RFB

=

VOUT – 1.215V

83.3µA

Step 10:

RT

RT

=

87.6

fOSC

– 1;

fOSC

in MHz

and RT

in kΩ

Step 11:

PMOS

Only needed for input or output disconnect. See PMOS

Selection in the Appendix for information on sizing the PMOS

and the biasing resistor, RGATE.

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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