LT3471

4

3471fb

FB1N (Pin 1): Negative Feedback Pin for Switcher 1.

Connect resistive divider tap here. Minimize trace area at

for inverting topologies.

FB1P (Pin 2): Positive Feedback Pin for Switcher 1. Connect

to a resistive divider tap for inverting topologies.

1mA of current. Do not pull this pin high. Must be locally

bypassed with

no less than 0.01μF and no more than 1μF.

A 0.1μF ceramic capacitor is recommended. Use this pin

as the positive feedback reference or connect a resistor

divider here for a smaller reference voltage.

FB2P (Pin 4): Same as FB1P but for Switcher 2.

FB2N (Pin 5): Same as FB1N but for Switcher 2.

SW2 (Pin 6): Switch Pin for Switcher 2 (Collector of in-

ternal NPN power switch). Connect inductor/diode here

and minimize the metal trace area connected to this pin

to minimize EMI.

SHDN/SS2 (Pin 7): Shutdown and Soft-Start Pin. Tie to

1.8V or more to enable device. Ground to shut down. Soft-

start function is provided when the voltage at this pin is

ramped slowly to 1.8V with an external RC circuit.

SHDN/SS1(Pin9):SameasSHDN/SS2butforSwitcher 1.

Note: taking either SHDN/SS pin high will enable the part.

Each switcher is individually enabled with its respective

SHDN/SS pin.

SW1 (Pin 10): Same as SW2 but for Switcher 1.

Exposed Pad (Pin 11): Ground. Connect directly to local

ground plane. This ground plane also serves as a heat

sink for optimal thermal performance.

TYPICAL PERFORMANCE CHARACTERISTICS

Oscillator Frequency

vs Temperature

Peak Switch Current

vs SHDN/SS Voltage

Start-Up Waveform

(Figure 2 Circuit)

TEMPERATURE (°C)

–50

1.00

1.05

1.15

1.20

1.25

1.50

1.35

0

50

75

3471 G07

1.10

1.40

1.45

1.30

–25

25

100

125

0

1.2

1.6

2.0

1.6

3471 G08

0.8

0.4

1.0

1.4

1.8

0.6

0.2

0

0.4

0.2

0.8

0.6

1.2 1.4

1.8

1

2.0

0.5ms/DIV

3471 G09

1A/DIV

2V/DIV

5V/DIV

CONTROL 1

AND 2

5V/DIV

PIN FUNCTIONS