LT3757 datasheet(6/24 Pages) AD

6 / 24 page

LT8300

Rev. A

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PIN FUNCTIONS

EN/UVLO (Pin 1): Enable/Undervoltage Lockout. The

EN/UVLO pin is used to enable the LT8300. Pull the pin

below 0.3V to shut down the LT8300. This pin has an

accurate 1.223V threshold and can be used to program a

VIN undervoltage lockout (UVLO) threshold using a resis-

tor divider from VIN to ground. A 2.5µA current hysteresis

allows the programming of VIN UVLO hysteresis. If neither

function is used, tie this pin directly to VIN.

GND (Pin 2): Ground. Tie this pin directly to local ground

plane.

RFB (Pin 3): Input Pin for External Feedback Resistor.

Connect a resistor from this pin to the transformer

primary SW pin. The ratio of the RFB resistor to the inter-

nal trimmed 12.23k resistor, times the internal bandgap

reference, determines the output voltage (plus the effect

of any non-unity transformer turns ratio). Minimize trace

area at this pin.

SW (Pin 4): Drain of the 150V Internal DMOS Power

Switch. Minimize trace area at this pin to reduce EMI and

voltage spikes.

VIN (Pin 5): Input Supply. The VIN pin supplies current

to internal circuitry and serves as a reference voltage for

the feedback circuitry connected to the RFB pin. Locally

bypass this pin to ground with a capacitor.

BLOCK DIAGRAM

8300 BD

OSCILLATOR

1:4

1.223V

25µA

BOUNDARY

DETECTOR

DRIVER

–

RSENSE

0.3Ω

RREF

12.23kΩ

RFB

2.5µA

EN/UVLO

1.223V

REFERENCE

REGULATORS

VIN

GND

RFB

VIN

NPS:1

DOUT

LSEC

LPRI

VOUT+

VOUT–

•

COUT

CIN

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