LT3758_15 Datasheet, PDF (8/36 Pages) Linear Technology – High Input Voltage, Boost, Flyback, SEPIC and Inverting Controller

LT3758/LT3758A
Pin Functions
V_C (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 compensation
pin voltage (V_C) 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 INTV_CC 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 R_T 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 bypassed 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 INTV_CC and GND. Driven to GND when
IC is shut down, during thermal lockout or when INTV_CC
is above or below the overvoltage or UV thresholds,
respectively.
INTV_CC (Pin 8): Regulated Supply for Internal Loads and
Gate Driver. Supplied from V_IN and regulated to 7.2V (typi-
cal). INTV_CC must be bypassed with a minimum of 4.7µF
capacitor placed close to pin. INTV_CC can be connected
directly to V_IN, if V_IN is less than 17.5V. INTV_CC can also
be connected to a power supply whose voltage is higher
than 7.5V, and lower than V_IN, 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 V_IN quiescent current below 1µA.
V_IN (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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