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LTC3375

3375fc

For more information www.linear.com/3375

operaTion

feedback network connected to the FB1 pin programs

the output voltage to 1.2V. The FB2 pin is tied to V

IN1/2

which configures buck regulator 2 as the slave. The SW1

and SW2 pins must be tied together, as must the V

IN1

and

IN2

pins. The register contents of the master program,

the combined buck regulator’s behavior, and the register

contents of the slave are ignored. The slave buck control

circuitry draws no current. The enable of the master buck

(EN1) controls the operation of the combined bucks; the

enable of the slave regulator (EN2) must be tied to ground.

Any combination of 2, 3, or 4 adjacent buck regulators

may be combined to provide either 2A, 3A, or 4A of aver

age output load current. For example, buck regulator 1

and buck regulator 2 may run independently

, while buck

regulators 3 and 4 may be combined to provide 2A, while

buck regulators 5 through 8 may be combined to provide

4A. Buck regulator 1 is never a slave, and buck regulator

is never a master. 15 unique output power stage configu

rations are possible to maximize application flexibility.

The LTC3375 is in an off state when it is powered up with

all regulators in shutdown. The ON pin is LOW in the off

state. The ON pin will go HIGH if PB is pulled LOW for

200ms. The ON pin stays in its HIGH state for 10 seconds

and then returns LOW unless KILL is asserted HIGH in

this time in which case ON will remain HIGH. If KILL goes

LOW, for longer than a 50ms debounce time, while ON is

HIGH after the 10 second time has expired, ON will again

go to its LOW state. PB being held low causes the KILL

pin to be ignored.

Once in the “on” state (ON pin is HIGH), the LTC3375 can

be powered down in one of three ways that allow for flex

ibility between hardware and software system resets. First,

if PB

is held LOW for at least 10 seconds, then ON will

be driven LOW. This will not force a hard reset on any of

the buck switching regulators. The ON pin, however, may

be used to either drive the EN pin of the first sequenced

buck converter or that of an upstream high voltage buck

switching regulator. In this case the IRQ pin is latched to

its LOW state to indicate a PB induced reset. Second, if

the PB pin is driven LOW for longer than 50ms but less

than 10 seconds, the IRQ pin will be pulled LOW for as

long as the PB pin remains LOW. If a microcontroller sees

a transient IRQ LOW signal, then this should signal that

the user has pressed the PB. A software power-down may

then be initiated if so desired. Finally, if the KILL input is

driven LOW for longer than 50ms, then a hard reset will

be initiated. All enabled buck switching regulators will

be turned off while KILL is low and will remain powered

down for 1 second after KILL returns high. KILL being

low also forces a hard reset while the pushbutton is in the

“off” state. A hard reset may also be generated by using

the RESET_ALL I

C command that will last for 1 second.

The pushbutton will return to the “off” state. KILL must be

high to power-up using EN pins or I

C. In any hard reset

event all buck regulator I

C bits are set low.

Power-Up and Power-Down Via Pushbutton

The LTC3375 may be turned on and off using the PB,

KILL, and ON pins as shown in Figures 2a and 2b. In

Figures2a and 2b, pressing PB LOW at time t

, causes

the ON pin to go HIGH at time t

and stay HIGH for at least

10 seconds after which ON will go LOW unless KILL has

been asserted high. ON can be connected to the EN pin

BUCK REGULATOR 1

(MASTER)

SW1

OUT

1.2V

475k

725k

FB1EN1

IN1

BUCK REGULATOR 2

(SLAVE)

SW2

EN2 FB2

3375 F01

IN2

Figure 1. Buck Regulators Configured as Master-Slave

Pushbutton Interface

The LTC3375 includes a pushbutton interface which can

be used to provide power-up or power-down control

for either the part or the application. The PB, KILL, and

ON pins provide the user with flexibility to power-up or

power-down the part in addition to having I

C control. All

PB timing parameters are scaled using the CT pin. Times

described below apply to a nominal C

capacitor of 0.01µF.

1 2 ... 12 13 14 15 16 17 18 19 20 21 22 ... 35 36

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DCS WDI Spécifications Page 17

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