LTC1439 查看數據表（PDF） - Linear Technology

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LTC1439

Dual High Efficiency, Low Noise, Synchronous Step-Down Switching Regulators

Linear Technology 

LTC1438/LTC1439

PIN FUNCTIONS

SENSE+ 1, SENSE+ 2: The (+) Input to Each Current

Comparator. Built-in offsets between SENSE– 1 and

SENSE+ 1 pins in conjunction with RSENSE1 set the current

trip threshold (same for second controller).

VOSENSE1,2: Receives the remotely sensed feedback volt-

age either from the output directly or from an external

resistive divider across the output. The VPROG2 pin deter-

mines which point VOSENSE2 must connect to. The VOSENSE1

pin, only available on the LTC1438-ADJ, requires an

external resistive divider to set the output voltage.

VPROG1, VPROG2: Programs Internal Voltage Attenuators

for Output Voltage Sensing. The voltage sensing for

thefirst controller is internally connected to SENSE– 1

while the VOSENSE2 pin allows for remote sensing for the

second controller. For VPROG1, VPROG2 < VINTVCC/3, the

divider is set for an output voltage of 3.3V. With VPROG1,

VPROG2 > VINTVCC/1.5 the divider is set for an output

voltage of 5V. Leaving VPROG2 open (DC) allows the

output voltage of the second controller to be set by an

external resistive divider connected to VOSENSE2.

COSC: External capacitor COSC from this pin to ground sets

the operating frequency.

ITH1, ITH2: Error Amplifier Compensation Point. Each

associated current comparator threshold increases with

this control voltage.

RUN/SS1, RUN/SS2: Combination of Soft Start and Run

Control Inputs. A capacitor to ground at each of these pins

sets the ramp time to full current output. The time is

approximately 0.5s/µF. Forcing either of these pins below

1.3V causes the IC to shut down the circuitry required for

that particular controller. Forcing both of these pins below

1.3V causes the device to shut down completely. For

applications which require 5V keep-alive, refer to the

LTC1538-AUX/LTC1539.

TGL1, TGL2: High Current Gate Drives for Main Top

N-Channel MOSFET. These are the outputs of floating

drivers with a voltage swing equal to INTVCC superim-

posed on the switch node voltage SW1 and SW2.

TGS1, TGS2: Gate Drives for Small Top N-Channel

MOSFET. These are the outputs of floating drivers with a

voltage swing equal to INTVCC superimposed on the

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switch node voltage SW. Leaving TGS1 or TGS2 open

invokes Burst Mode operation for that controller.

BG1, BG2: High Current Gate Drive Outputs for Bottom

N-Channel MOSFETs. Voltage swing at these pins is from

ground to INTVCC.

SFB1: Secondary Winding Feedback Input. This input acts

only on the first controller and is normally connected to a

feedback resistive divider from the secondary winding.

Pulling this pin below 1.19V will force continuous syn-

chronous operation for the first controller. This pin should

be tied to: ground to force continuous operation; INTVCC

in applications that don’t use a secondary winding; and a

resistive divider from the output in applications using a

secondary winding.

POR2: This output is a drain of an N-channel pull-down.

This pin sinks current when the output voltage of the

second controller drops 7.5% below its regulated voltage

and releases 65536 oscillator cycles after the output

voltage of the second controller rises to within –5% value

of its regulated value. The POR2 output is asserted when

RUN/SS1 and RUN/SS2 are both low, independant of the

VOUT2. This pin is not functional on the LTC1438X.

LBO: This output is a drain of an N-channel pull-down.

This pin will sink current when the LBI pin goes below

1.19V.

LBI: The (+) input of a comparator which can be used as

a low-battery voltage detector. The (–) input is connected

to the 1.19V internal reference.

PLLIN: External Synchronizing Input to Phase Detector.

This pin is internally terminated to SGND with 50kΩ. Tie

this pin to SGND in applications which do not use the

phase-locked loop.

PLL LPF: Output of Phase Detector and Control Input of

Oscillator. Normally a series RC lowpass filter network is

connected from this pin to ground. Tie this pin to SGND in

applications which do not use the phase-locked loop. Can

be driven by a 0V to 2.4V logic signal for a frequency

shifting option.

AUXFB: Feedback Input to the Auxiliary Regulator/Com-

parator. When used as a linear regulator, this input can

either be connected to an external resistive divider or

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