LT3973 Просмотр технического описания (PDF) - Linear Technology

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LT3973

42V, 750mA Step-Down Regulator with 2.5µA Quiescent Current and Integrated Diodes

Linear Technology 

LT3973/LT3973-3.3/LT3973-5

PIN FUNCTIONS

FB (Pin 1, LT3973 Only): The LT3973 regulates the FB

pin to 1.21V. Connect the feedback resistor divider tap

to this pin.

VOUT (Pin 1, LT3973-3.3 and LT3973-5 Only): The

LT3973-3.3 and LT3973-5 regulate the VOUT pin to 3.3V

and 5V, respectively. This pin connects to the internal

feedback divider that programs the fixed output voltage.

OUT (Pin 2): The LT3973 regulates the VIN to VOUT voltage

for dropout conditions. It will also pull current from this

pin to charge the boost capacitor when needed. Connect

this pin to the output. If programmed output is greater

than 14V, tie this pin to GND.

EN/UVLO (Pin 3): The part is in shutdown when this pin is

low and active when this pin is high. The threshold voltage

is 1.19V going up with 30mV of hysteresis. Tie to VIN if

shutdown feature is not used. The EN/UVLO threshold is

accurate only when VIN is above 4.2V. If VIN is lower than

4.2V, ground EN/UVLO to place the part in shutdown.

VIN (Pin 4): The VIN pin supplies current to the LT3973’s

internal circuitry and to the internal power switch. This

pin must be locally bypassed.

GND (Pin 5, Exposed Pad Pin 11): Ground. The exposed

pad must be soldered to the PCB.

SW (Pin 6): The SW pin is the output of an internal power

switch. Connect this pin to the inductor.

BOOST (Pin 7): This pin is used to provide a drive volt-

age, higher than the input voltage, to the internal bipolar

NPN power switch.

BD (Pin 8): This pin connects to the anode of the boost

diode. This pin also supplies current to the LT3973’s

internal regulator when BD is above 3.2V.

PG (Pin 9): The PG pin is the open-drain output of an

internal comparator. PG remains low until the FB pin is

within 10% of the final regulation voltage. PG is valid when

VIN is above 4.2V and EN/UVLO is high.

RT (Pin 10): A resistor is tied between RT and ground to

set the switching frequency.

For more information www.linear.com/LT3973

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