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LT3580

3580fg

TYPICAL PERFORMANCE CHARACTERISTICS

SHDN Pin Current

Active/Lockout Threshold

TA = 25°C unless otherwise specified

PIN FUNCTIONS

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

boost or inverting converter, tie a resistor from the FB pin

to VOUT according to the following equations:

FB =

OUT − 1.215

()

83.3 • 10−

; Boost or SEPIC Converter

FB =

OUT + 5mV

()

83.3 • 10−

; Inverting Converter

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

compensation 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 1.24V (LT3580E, LT3580I) or 1.22V

(LT3580H, LT3580MP) to disable the chip. Drive above

1.38V (LT3580E, LT3580I) or 1.40V (LT3580H, LT3580MP)

to activate 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 (Pin 7): Soft-Start Pin. Place a soft-start capacitor here.

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

275k resistor to about 2.2V.

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 the

Applications Information section for more information.

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

be soldered directly to local ground plane.

SHDN VOLTAGE (V)

0.5

–50°C

1.5

3580 G10

100°C

20°C

SHDN VOLTAGE (V)

200

250

–50°C

20°C

100°C

300

3580 G11

150

100

510

TEMPERATURE (°C)

–50

1.20

1.22

1.26

1.28

1.30

1.40

1.34

3580 G12

1.24

1.36

1.38

1.32

100

SHDN RISING

SHDN FALLING

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