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LT3579IUFD-1-PBF

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

Linear Technology 

LT3579/LT3579-1

APPLICATIONS INFORMATION

Use the following equations to calculate the FB resistor

for 2-phase converters:

RFB

=

⎛

⎜

⎝

VOUT

2•

– 1.215V

83.3μA

⎞

⎟;

⎠

Boost or SEPIC

Multiphase Converter

RFB

=

⎛|

⎜

⎝

VOUT | + 9mV

2 • 83.3μA

⎞

⎟;

⎠

Inverting Multiphase

Converter

Note that the CLKOUT pin on the LT3579-1 runs at a fixed

duty cycle of ~50%. If monitoring the die temperature is

desired, the slave IC can be a LT3579.

It is possible to use the LT3579-1 in a multiphase converter

of more than 2 phases. Consult the LTC Applications

Engineering Department for more information.

CHARGE PUMP AIDED REGULATORS

Designing charge pumps with the LT3579 can offer efficient

solutions with fewer components than traditional circuits

because of the master/slave switch configuration on the

IC. The current in the master switch (SW1) is sensed by

the current comparator (A4 in Block Diagram), but the

current in the slave switch (SW2) is not. Note that the slave

switch, SW2, operates in phase with SW1. This method

of operation by the master/slave switches can offer the

following benefits to charge pump designs:

• The slave switch, by not performing a current sense

operation like the master switch, can sustain fairly

large current spikes when the flying capacitors charge

up. Since this current spike flows through SW2, it

does not affect the operation of the current comparator

(A4 in Block Diagram).

• The master switch, immune from the capacitor current

spike, can sense the inductor current more accurately.

• Since the slave switch can sustain large current spikes,

the diodes that feed current into the flying capacitors

do not need current limiting resistors, leading to

efficiency and thermal improvements.

22

4.7μH

10μF

4.7μF

SW1 SW2

VIN

FAULT

CLKOUT

FB

LT3579-1

SLAVE

SHDN

GATE

RT

VC

SYNC GND SS

4.7μF

s2

VPWR

12V

VIN

5V

86.6k

0.22μF

VOUT1

4.7μH

6.4k

10μF

4.7μF

s2

VOUT1 100k

500k

21.5k

4.7μF

SW1 SW2

VIN

CLKOUT

FAULT

FB

LT3579-1

MASTER

SHDN

GATE

RT

VC

SYNC GND SS

137k

VPWR

47pF 7k

5k

86.6k

0.22μF

2.2nF

VOUT

24V

3.7A,

89W

4.7μF

s2

3579 F13

Figure 13. 2-Phase Converters Using LT3579-1

High VOUT Charge Pump Topology

The LT3579 can be used in a charge-pump topology (refer

to Figure 16), multiplying the output of an inductive boost

converter. The master switch (SW1) can be used to drive

the inductive boost converter, while the slave switch (SW2)

can be used to drive one or more charge pump stages. This

topology is useful for high voltage applications including

VFD Bias Supplies.

Single Inductor Inverting Topology

If there is a need to use just 1 inductor to generate a

negative output voltage whose magnitude is greater than

VIN, the Single Inductor Inverting topology (shown in

Figure 15) can be used. Since the master and slave switches

are isolated by an external Schottky diode, the current spike

through C1 will flow through the slave switch, thereby

preventing the current comparator (A4 in Block Diagram)

from falsely tripping. Output disconnect is inherently built

into the single inductor topology.

35791f

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