Datasheet
LT3471
4
3471fb
FB1N (Pin 1): Negative Feedback Pin for Switcher 1.
Connect resistive divider tap here. Minimize trace area at
FB1N. Set V
OUT
= V
FB1P
(1 + R1/R2), or connect to ground
for inverting topologies.
FB1P (Pin 2): Positive Feedback Pin for Switcher 1. Connect
either to V
REF
or a divided down version of V
REF
, or connect
to a resistive divider tap for inverting topologies.
V
REF
(Pin 3): 1.00V Reference Pin. Can supply up to
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. Sof t-
start function is provided when the voltage at this pin is
ramped slowly to 1.8V with an external RC circuit.
V
IN
(Pin 8): Input Supply. Must be locally bypassed.
SHDN/SS1 (Pin 9): Same as SHDN/SS2 but for Switcher 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
FREQUENCY (MHz)
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
V
SHDN/SS
(V)
0
SWITCH CURRENT (A)
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
0.40.2
0.80.6
1.2 1.4 1.8
1
2.0
T
A
= 25°C
0.5ms/DIV
3471 G09
I
SUPPLY
1A/DIV
V
OUT1
2V/DIV
V
OUT2
5V/DIV
CONTROL 1
AND 2
5V/DIV
PIN FUNCTIONS