LT3758 datasheet(9/36 Pages) LINER

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LT3758

3758f

PIN FUNCTIONS

VC (Pin 1): Error Ampliﬁer Compensation Pin. Used to

stabilize the voltage loop with an external RC network.

FBX (Pin 2): Positive and Negative Feedback Pin. Re-

ceives the feedback voltage from the external resistor

divider across the output. Also modulates the switching

frequency during start-up and fault conditions when FBX

is close to GND.

SS (Pin 3): Soft-Start Pin. This pin modulates compensa-

tion pin voltage (VC) clamp. The soft-start interval is set

with an external capacitor. The pin has a 10μA (typical)

pull-up current source to an internal 2.5V rail. The soft-

start pin is reset to GND by an undervoltage condition

at SHDN/UVLO, an INTVCC undervoltage or overvoltage

condition or an internal thermal lockout.

RT (Pin 4): Switching Frequency Adjustment Pin. Set the

frequency using a resistor to GND. Do not leave this pin

open.

SYNC (Pin 5): Frequency Synchronization Pin. Used to

synchronize the switching frequency to an outside clock.

If this feature is used, an RT resistor should be chosen to

program a switching frequency 20% slower than the SYNC

pulse frequency. Tie the SYNC pin to GND if this feature is

not used. SYNC is ignored when FBX is close to GND.

SENSE (Pin 6): The Current Sense Input for the Control

Loop. Kelvin connect this pin to the positive terminal of

the switch current sense resistor in the source of the NFET.

The negative terminal of the current sense resistor should

be connected to GND plane close to the IC.

GATE (Pin 7): N-Channel MOSFET Gate Driver Output.

Switches between INTVCC and GND. Driven to GND when

IC is shut down, during thermal lockout or when INTVCC

is above or below the overvoltage or UV thresholds,

respectively.

INTVCC (Pin 8): Regulated Supply for Internal Loads and

Gate Driver. Supplied from VIN and regulated to 7.2V (typi-

cal). INTVCC must be bypassed with a minimum of 4.7μF

capacitor placed close to pin. INTVCC can be connected

directly to VIN, if VIN is less than 17.5V. INTVCC can also

be connected to a power supply whose voltage is higher

than 7.5V, and lower than VIN, provided that supply does

not exceed 17.5V.

SHDN/UVLO (Pin 9): Shutdown and Undervoltage Detect

Pin. An accurate 1.22V (nominal) falling threshold with

externally programmable hysteresis detects when power

is okay to enable switching. Rising hysteresis is generated

by the external resistor divider and an accurate internal

2μA pull-down current. An undervoltage condition resets

sort-start. Tie to 0.4V, or less, to disable the device and

reduce VIN quiescent current below 1μA.

VIN (Pin 10): Input Supply Pin. Must be locally bypassed

with a 0.22μF, or larger, capacitor placed close to the

pin.

Exposed Pad (Pin 11): Ground. This pin also serves

as the negative terminal of the current sense resistor.

The Exposed Pad must be soldered directly to the local

ground plane.

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