LTC1876 datasheet(8/36 Pages) LINER

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LTC1876

1876fa

RUN/SS1, RUN/SS2 (Pins 1, 23): Combination of Soft-Start,

Run Control Inputs and Short-Circuit Detection Timers. A

capacitor to ground at each of these pins sets the ramp time

to full output current. Forcing either of these pins back below

1V causes the IC to shut down the circuitry required for that

particular controller. Latchoff overcurrent protection is also

invoked via this pin as described in the Applications Informa-

tion section.

SENSE1+, SENSE2+ (Pins 2, 14): The (+) Input to each

Differential Current Comparator. The ITH pin voltage and

controlled offsets between the SENSE– and SENSE+ pins in

conjunction with RSENSE set the current trip threshold.

SENSE1–, SENSE2– (Pins 3, 13): The (–) Input to the

Differential Current Comparators.

VOSENSE1, VOSENSE2 (Pins 4, 12): Receives the remotely-

sensed feedback voltage for each controller from an external

resistive divider across the output.

FREQSET (Pin 5): Frequency Control Input to the Oscillator.

This pin can be left open, tied to ground, tied to INTVCC or

drivenbyanexternalvoltagesource.Thispincanalsobeused

with an external phase detector to build a true phase-locked

loop.

STBYMD (Pin 6): Control pin that determines which circuitry

remains active when the controllers are shut down and/or

TYPICAL PERFOR A CE CHARACTERISTICS

PIN FUNCTIONS

VIN = 15V

VOUT = 5V

LOAD STEP = 0A TO 3A

Burst Mode OPERATION

µs/DIV

1876 G30

VOUT

200mV/DIV

IOUT

2A/DIV

Load Step (Figure 1)

Constant Frequency (Burst

Inhibit) Operation (Figure 1)

Input Source/Capacitor

Instantaneous Current (Figure 1)

Burst Mode Operation (Figure 1)

IIN

2A/DIV

VIN

200mV/DIV

VSW2

10V/DIV

VIN = 15V

VOUT = 5V

IOUT5 = IOUT3.3 = 2A

µs/DIV

1876 G31

VSW1

10V/DIV

VOUT

20mV/DIV

IOUT

0.5A/DIV

VIN = 15V

VOUT = 5V

VFCB = OPEN

IOUT = 20mA

µs/DIV

1876 G32

VOUT

20mV/DIV

IOUT

0.5A/DIV

VIN = 15V

VOUT = 5V

VFCB = 5V

IOUT = 20mA

µs/DIV

1876 G33

VIN = 15V

VOUT = 5V

LOAD STEP = 0A TO 3A

CONTINUOUS MODE

Load Step (Figure 1)

VOUT

200mV/DIV

IOUT

2A/DIV

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