lt3680 Linear Technology Corporation, lt3680 Datasheet - Page 7

• Manufacturer Part Number: lt3680
• Description: 36v, 3.5a, 2.4mhz Step-down Switching Regulator With 75?a Quiescent Current
• Manufacturer: Linear Technology Corporation

PI FU CTIO S
BLOCK DIAGRA
BD (Pin 1): This pin connects to the anode of the boost
Schottky diode. BD also supplies current to the internal
regulator.
BOOST (Pin 2): This pin is used to provide a drive
voltage, higher than the input voltage, to the internal bipolar
NPN power switch.
SW (Pin 3): The SW pin is the output of the internal power
switch. Connect this pin to the inductor, catch diode and
boost capacitor.
V
internal regulator and to the internal power switch. This
pin must be locally bypassed.
RUN/SS (Pin 5): The RUN/SS pin is used to put the
LT3680 in shutdown mode. Tie to ground to shut down
the LT3680. Tie to 2.5V or more for normal operation. If
the shutdown feature is not used, tie this pin to the V
pin. RUN/SS also provides a soft-start function; see the
Applications Information section.
IN
V
U
IN
(Pin 4): The V
R
C1
T
U
10
4
5
6
7
V
RUN/SS
RT
SYNC
PG
IN
IN
SOFT-START
pin supplies current to the LT3680’s
U
GND
11
INTERNAL 0.79V REF
W
+
–
R2
0.7V
8
FB
R1
ERROR AMP
+
–
Σ
200kHzTO2.4MHz
SLOPE COMP
OSCILLATOR
–
+
IN
SYNC (Pin 6): This is the external clock synchronization
input. Ground this pin for low ripple Burst Mode operation
at low output loads. Tie to a clock source for synchroniza-
tion. Clock edges should have rise and fall times faster
than 1μs. Do not leave pin fl oating. See synchronizing
section in Applications Information.
PG (Pin 7): The PG pin is the open collector output of an
internal comparator. PG remains low until the FB pin is
within 9% of the fi nal regulation voltage. PG output is valid
when V
FB (Pin 8): The LT3680 regulates the FB pin to 0.790V.
Connect the feedback resistor divider tap to this pin.
V
amplifi er. 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 10): Oscillator Resistor Input. Connecting a resistor
to ground from this pin sets the switching frequency.
Exposed Pad (Pin 11): Ground. The Exposed Pad must
be soldered to PCB.
C
(Pin 9): The V
BurstMode
V
R
S
SWITCH
IN
C
LATCH
DETECT
CLAMP
is above 3.6V and RUN/SS is high.
DISABLE
Q
C
pin is the output of the internal error
BOOST
SW
BD
V
C
1
2
3
9
D1
R
C
C
C
C3
L1
C
F
LT3680
C2
3680 BD
V
OUT
7
3680f