LT8580 datasheet(6/32 Pages) LINER

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LT8580

8580fa

For more information www.linear.com/LT8580

block DiagraM

pin FuncTions

FBX (Pin 1): Positive and Negative Feedback Pin. For a

noninverting or inverting converter, tie a resistor from the

FBX pin to VOUT according to the following equations:

RFBX=

VOUT −1.204V

(

)

83.3µA

; Noninverting Converter

RFBX=

VOUT + 3mV

(

)

83.3µA

; Inverting Converter

VC (Pin 2): Error Amplifier Output Pin. Tie external com-

pensation network to this pin.

VIN (Pin 3): Input Supply Pin. Must be locally bypassed.

SW (Pin 4): Switch Pin. This is the collector of the internal

NPN Power switch. Minimize the metal trace area connec-

ted to this pin to minimize EMI.

SHDN (Pin 5): Shutdown Pin. In conjunction with the

UVLO (undervoltage lockout) circuit, this pin is used

to enable/disable the chip and restart the soft-start

sequence. Drive below 1.21V to disable the chip. Drive

above 1.40V to activate the chip and restart the soft-start

sequence. Do not float this pin.

RT (Pin 6): Timing Resistor Pin. Adjusts the switching

frequency. Place a resistor from this pin to ground to set

the frequency to a fixed free running level. Do not float

this pin.

SS(Pin7):Soft-StartPin.Placeasoft-startcapacitorhere.

Upon start-up, the SS pin will be charged by a (nominally)

280k resistor to about 2.1V.

SYNC (Pin 8): To synchronize the switching frequency to

an outside clock, simply drive this pin with a clock. The

high voltage level of the clock needs to exceed 1.3V, and

the low level should be less 0.4V. Drive this pin to less

than 0.4V to revert to the internal free-running clock. See

theApplicationsInformationsectionformoreinformation.

GND (Exposed Pad Pin 9): Ground. Exposed pad must

be soldered directly to local ground plane.

–

∑

1.204V

REFERENCE

ADJUSTABLE

OSCILLATOR

FREQUENCY

FOLDBACK

SLOPE

COMPENSATION

COMPARATOR

DISCHARGE

DETECT

280k

SR2

14.5k

SR1

SYNC

÷N

SHDN

FBX

1.3V

0.02

GND

RFBX

DRIVER

ILIMIT

VIN

VOUT

CSS

CIN

VIN

SOFT-

START

SYNC

BLOCK

UVLO

8580 BD

50k

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