LTC4350IGN datasheet(6/18 Pages) LINER

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LTC4350

4350fb

pin FuncTions

GND (Pin 8): Chip Ground.

FB (Pin 9): Analog Error Amplifier Input (E/A1). This pin is

used to monitor the output supply voltage with an external

resistive divider. The FB pin voltage is compared to 1.220V

reference. The difference between the FB pin voltage and

the reference is amplified and output on the COMP1 pin.

RSET (Pin 10): Analog Output Pin. The IOUT amplifier

converts the voltage at the COMP2 pin (down a diode

voltage) to the RSET pin. Therefore, the current through

the external resistor (RSET) placed between the RSET pin

and ground is (COMP2 – VDIODE)/RSET. This current is

used to adjust the output voltage.

IOUT (Pin 11): Analog Output Pin. The current flowing into

the IOUT pin is equal to the current flowing out of the RSET

pin that was set by the external resistor RSET. This current

is used to adjust the output supply voltage by modifying

the voltage sensed by the power supply’s internal voltage

feedback circuitry.

R– (Pin 12): Analog Input Pin. With a sense resistor placed

in the supply path between the R+ and R– pins, the power

supply current is measured as a voltage drop between R+

and R–. This voltage is measured by the ISENSE block and

multiplied at the GAIN pin.

R+ (Pin 13): Analog Input Pin. With a sense resistor placed

in the supply path between the R+ and R– pins, the power

supply current is measured as a voltage drop between R+

and R–. This voltage is measured by the ISENSE block and

multiplied at the GAIN pin.

GATE (Pin14): The high side gate drive for the external

N-Channel power FET. An internal charge pump provides

the gate drive necessary to drive the FETs. The slope of

the voltage rise or fall at the GATE is set by an external

capacitor connected between GATE and GND, and the

10µAchargepumpoutputcurrent.Whentheundervoltage

lockout circuit monitoring VCC trips, the OV pin is pulled

high or the UV pin is pulled low, the GATE pin is immedi-

ately pulled to GND.

STATUS (Pin 15): Open-Drain Digital Output. The STATUS

pin has an open-drain output to GND. This pin is pulled

low to indicate a fault has occurred in the system. There

arethreetypesoffaults.Thefirstisaundervoltagelockout

on VCC or the UV pin is low while the output voltage is

active. The second is when the COMP2 pin is above 1.5V

or below 0.5V and the voltage on the GAIN pin is greater

than 100mV. The final failure is when the OV pin is high.

The three faults will activate the pull-down on the STATUS

pin after a timing cycle.

VCC (Pin 16): The Positive Supply Input, Ranging from

3.3V to 12V for Normal Operation. ICC is typically 1.6mA.

An undervoltage lockout circuit disables the chip until

the voltage at VCC is greater than 2.47V. A 0.1µF bypass

capacitor is required on the VCC pin. If the VCC pin is tied

to the same power supply output that is being adjusted,

then a 51Ω decoupling resistor is needed to hold up the

supply during a short to ground on the supply output.

VCC must be greater than or equal to the supply that is

connected to the R+ and R– pins.

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