LTM8056 datasheet(10/42 Pages) LINER

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LTC7813

7813f

For more information www.linear.com/LTC7813

pin FuncTions

SW1, SW2 (Pins 1, 30): Switch Node Connections to

Inductors.

TG1, TG2 (Pins 2, 29): High Current Gate Drives for Top

N-Channel MOSFETs. These are the outputs of floating

driverswithavoltageswingequaltoDRVCCsuperimposed

on the switch node voltage SW.

TRACK/SS1, SS2 (Pins 3, 23): External Tracking and Soft-

Start Input. For the buck channel, the LTC7813 regulates

the VFB1 voltage to the smaller of 0.8V, or the voltage on

the TRACK/SS1 pin. For the boost channel, the LTC7813

regulates the VFB2 voltage to the smaller of 1.2V, or the

voltage on the SS2 pin. An internal 10µA pull-up current

source is connected to this pin. A capacitor to ground at

thispinsetstheramptimetofinalregulatedoutputvoltage.

Alternatively, a resistor divider on another voltage supply

connectedtotheTRACK/SS1pinallowstheLTC7813buck

output to track the other supply during start-up.

VPRG2 (Pin 4): Channel 2 Output Control Pin. This pin

sets the boost channel to adjustable output mode using

external feedback resistors or fixed 10V/12V output mode

using internal resistive dividers. Grounding this pin allows

the output to be programmed through the VFB2 pin using

external resistors, regulating VFB2 to the 1.2V reference.

Floating this pin or connecting it to INTVCC programs the

output to 10V or 12V (respectively), with VFB2 used to

sense the output voltage.

ITH1, ITH2 (Pins 5, 20): Error Amplifier Outputs and

Switching Regulator Compensation Points. Each associ-

ated channel’s current comparator trip point increases

with this control voltage.

VFB1(Pin6):Thispinreceivestheremotelysensedfeedback

voltage for the buck controller from an external resistive

divider across the output.

SENSE1+, SENSE2+ (Pins 7, 12): The (+) Input to the

Differential Current Comparators. The ITH pin voltage and

controlled offsets between the SENSE– and SENSE+ pins

in conjunction with RSENSE set the current trip threshold.

For the boost channel, the SENSE2+ pin supplies current

to the current comparator.

SENSE1–, SENSE2– (Pins 8, 13): The (–) Input to the

Differential Current Comparators. When SENSE1– for the

buck channel is greater than INTVCC, the SENSE1– pin

supplies current to the current comparator.

FREQ (Pin 9): The frequency control pin for the internal

VCO. Connecting this pin to GND forces the VCO to a fixed

low frequency of 350kHz. Connecting this pin to INTVCC

forces the VCO to a fixed high frequency of 535kHz.

Other frequencies between 50kHz and 900kHz can be

programmed using a resistor between FREQ and GND.

The resistor and an internal 20µA source current create a

voltage used by the internal oscillator to set the frequency.

Typical perForMance characTerisTics

Start-Up

Buck Inductor Current at Light

Load

Boost Inductor Current at Light

Load

5ms/DIV

VOUT

5V/DIV

RUN

5V/DIV

7813 G37

FIGURE 15 CIRCUIT

5µs/DIV

FIGURE 15 CIRCUIT

VIN = 32V

VOUT = 24V

IOUT = 1mA

IL1

2A/DIV

7813 G38

FORCED CONTINUOUS MODE

Burst Mode OPERATION

PULSE-SKIPPING MODE

5µs/DIV

FIGURE 15 CIRCUIT

VIN = 18V

VOUT = 24V

IOUT = 1mA

IL2

2A/DIV

7813 G39

FORCED CONTINUOUS MODE

Burst Mode OPERATION

PULSE-SKIPPING MODE

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