LT3474 datasheet(10/28 Pages) AD

10 / 28 page

LT3755/LT3755-1/LT3755-2

Rev. E

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RT (Pin 11/Pin 5): Switching Frequency Adjustment Pin.

Set the frequency using a resistor to GND (for resistor

values, see the Typical Performance curve or Table 1). Do

not leave the RT pin open.

SHDN/UVLO (Pin 12/Pin 6): Shutdown and Undervoltage

Detect Pin. An accurate 1.22V falling threshold with ex-

ternally programmable hysteresis detects when power is

OK to enable switching. Rising hysteresis is generated

by the external resistor divider and an accurate internal

2.1µA pull-down current. Above the threshold (but below

6V), SHDN/UVLO input bias current is sub-µA. Below the

falling threshold, a 2.1µA pull-down current is enabled so

theusercandefinethehysteresiswiththeexternalresistor

selection. An undervoltage condition resets soft-start.

Tie to 0.4V, or less, to disable the device and reduce VIN

quiescent current below 1µA.

INTVCC (Pin 13/Pin 7): Regulated Supply for Internal

Loads, GATE Driver and PWMOUT Driver. Supplied from

VIN and regulates to 7.15V (typical). INTVCC must be

bypassed with a 4.7µF capacitor placed close to the pin.

Connect INTVCC directly to VIN if VIN is always less than

or equal to 8V.

VIN (Pin 14/Pin 8): Input Supply Pin. Must be locally

bypassed with a 0.22µF (or larger) capacitor placed close

to the IC.

SENSE (Pin 15/Pin 9): The current sense input for the

control loop. Kelvin connect this pin to the positive ter-

minal of the switch current sense resistor, RSENSE, in the

source of the NFET. The negative terminal of the current

sense resistor should be Kelvin connected to the GND

plane of the IC.

GATE (Pin 16/Pin 10): N-channel FET Gate Driver Output.

Switches between INTVCC and GND. Driven to GND during

shutdown, fault or idle states.

ExposedPad(Pin17/Pin17):Ground.Thispinalsoserves

as current sense input for control loop, sensing negative

terminal of current sense resistor. Solder the Exposed Pad

directly to ground plane.

PIN FUNCTIONS (MSOP/QFN)

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