LT3506/LT3506A
TYPICAL PERFOR A CE CHARACTERISTICS
I
RUN/SS
vs Temperature
3.0
2.5
RUNN/SS THRESHOLDS (V)
RUN/SS CURRENT (µA)
2.0
1.5
1.0
0.5
0
–50
1.4
1.2
1.0
0.8
0.6
TO RUN
0.4
0.2
–25
0
25
50
75
TEMPERATURE (°C)
100
125
0
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
TO SWITCH
PI FU CTIO S
BOOST1 (Pin 1), BOOST2 (Pin 8):
The BOOST pins are
used to provide drive voltages, higher than the input
voltage, to the internal bipolar NPN power switches. Tie
through a diode from V
OUT
or from V
IN
.
SW1 (Pin 2), SW2 (Pin 7):
The SW pins are the outputs
of the internal power switches. Connect these pins to the
inductors, catch diodes and boost capacitors.
V
IN1
(Pins 3, 4):
The V
IN1
pins supply current to the
LT3506’s internal regulator and to the internal power
switch connected to SW1. These pins must be locally
bypassed.
V
IN2
(Pins 5, 6):
The V
IN2
pins supply current to the inter-
nal power switch connected to SW2 and must be locally
bypassed. Connect these pins directly to V
IN1
unless power
for Channel 2 is coming from a different source.
RUN/SS1 (Pin 13), RUN/SS2 (Pin 12):
The RUN/SS pins
are used to shut down the individual switching regula-
tors and the internal bias circuits. They also provide a
soft-start function. To shut down either regulator, pull the
RUN/SS pin to ground with an open drain or collector.
Tie a capacitor from these pins to ground to limit switch
current during start-up. If neither feature is used, leave
these pins unconnected.
U W
RUN/SS Thresholds vs
Temperature
3506 G12
3506 G13
U
U
U
PG1 (Pin 14), PG2 (Pin 11):
The Power Good pins are
the open collector outputs of an internal comparator. PG
remains low until the FB pin is within 10% of the final
regulation voltage. As well as indicating output regulation,
the PG pins can be used to sequence the two switching
regulators. These pins can be left unconnected. The PG
outputs are valid when V
IN
is greater than 3.4V and either
of the RUN/SS pins is high. The PG comparators are
disabled in shutdown.
V
C1
(Pin 15), V
C2
(Pin 10):
The V
C
pins are the outputs of
the internal error amps. The voltages on these pins control
the peak switch currents. These pins are normally used
to compensate the control loops, but can also be used to
override the loops. Pull these pins to ground with an open
drain to shut down each switching regulator.
FB1 (Pin 16), FB2 (Pin 9):
The LT3506 regulates each
feedback pin to 800mV. Connect the feedback resistor
divider taps to these pins.
Exposed Pad (Pin 17):
The Exposed Pad of the package
provides both electrical contact to ground and good thermal
contact to the printed circuit board. The Exposed Pad must
be soldered to the circuit board for proper operation.
3506afb
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