Datasheet

LT3980
7
3980fa
For more information www.linear.com/LT3980
SYNC (Pin 1/Pin 1): This is the external clock synchro-
nization input. Ground this pin for low ripple Burst Mode
operation at low output loads. Tie to a voltage above 0.8V
to select pulse-skipping mode. Tie to a clock source for
synchronization. Clock edges should have rise and fall
times faster than 1µs. Tie pin to GND if not used. See the
Synchronization section in Applications Information.
NC (Pins 2, 13/Pins 3, 5, 13, 16): No Connect. These
pins are not connected to internal circuitry.
PG (Pin 3/Pin 2): The PG pin is the open collector output
of an internal comparator. PG remains low until the FB pin
is within 9% of the final regulation voltage. PG output is
valid when V
IN
is above 3.6V and RUN/SS is high.
FB (Pin 4/Pin 4): The LT3980 regulates the FB pin to 0.790V.
Connect the feedback resistor divider tap to this pin.
V
C
(Pin 5/Pin 6): The V
C
pin is the output of the internal
error amplifier. The voltage on this pin controls the peak
switch current. Tie an RC network from this pin to ground
to compensate the control loop.
RT (Pin 6/Pin 7): Oscillator Resistor Input. Connecting
a resistor to ground from this pin sets the switching
frequency.
GND (Pin 7, 15/Pin 8, 17): Ground. The exposed pads
must be soldered to the PCB.
RUN/SS (Pin 8/Pin 9): The RUN/SS pin is used to put the
LT3980 in shutdown mode. Tie to ground to shut down
the LT3980. Tie to 2.5V or more for normal operation. If
the shutdown feature is not used, tie this pin to the V
IN
pin. RUN/SS also provides a soft-start function; see the
Applications Information section.
BD (Pin 9/Pin 10): This pin connects to the anode of the
boost Schottky diode. BD also supplies current to the
internal regulator.
BOOST (Pin 10/Pin 11): This pin is used to provide a drive
voltage, higher than the input voltage, to the internal bipolar
NPN power switch.
SW (Pin 11/Pin 12): The SW pin is the output of the
internal power switch. Connect this pin to the inductor,
catch diode and boost capacitor.
V
IN
(Pin 12/Pin 14): The V
IN
pin supplies current to the
LT3980’s internal regulator and to the internal power switch.
This pin must be locally bypassed.
DA (Pin 14/Pin 15): This pin measures catch diode current
and pauses the oscillator during overcurrent conditions.
+
+
+
OSCILLATOR
100kHzTO2.4MHz
BurstMode
DETECT
V
C
CLAMP
SOFT-START
SLOPE COMP
R
V
IN
V
IN
RUN/SS
BOOST
SW
SWITCH
LATCH
V
C
V
OUT
C2
C3
C
F
L1
D1
DISABLE
C
C
R
C
BD
RT
R2
GND
ERROR AMP
R1
FB
R
T
C1
PG
0.725V
S
Q
Σ
DA
3680 BD
INTERNAL 0.79V REF
SYNC
block DiaGram
pin FuncTions
(DFN, MSOP)
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