LTC3520 Linear Technology, LTC3520 Datasheet - Page 9

• Manufacturer Part Number: LTC3520
• Description: Synchronous 1A Buck-Boost and 600mA Buck Converters
• Manufacturer: Linear Technology

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PIN FUNCTIONS
SS2 (Pin 13): Buck Converter Soft-Start Pin. This pin must
be connected to a soft-start capacitor. The value of the
capacitor determines the duration of the soft-start period.
For information on choosing the value of this capacitor, see
the Applications Information section of this datasheet.
FB2 (Pin 14): Feedback Voltage for the Buck Converter.
This pin is derived from a resistor divider on the buck
output voltage. The buck output voltage is given by the
following equation where R1 is a resistor between FB2
and ground and R2 is a resistor between FB2 and the
buck output voltage:
V
quency compensation network is connected to FB1 to
compensate the loop. During Burst Mode operation, V
is driven internally by a clamp circuit.
SGND (Pin 16): Small Signal Ground. This pin is used
as a ground reference for the internal circuitry of the
LTC3520.
SS1 (Pin 17): Buck-Boost Converter Soft-Start Pin. This
pin must be connected to a soft-start capacitor. The value
of the capacitor determines the duration of the soft-start
period. For information on choosing the value of this
capacitor, see the Applications Information section of
this datasheet.
FB1 (Pin 18): Feedback Voltage for the Buck-Boost Con-
verter. This pin is derived from a resistor divider on the
buck-boost output voltage. The buck-boost output voltage
is given by the following equation where R1 is a resistor
C1
V
(Pin 15): Buck-Boost Error Amplifi er Output. A fre-
OUT
=
0 790
.
V
⎛
⎝ ⎜
1
+
R
R
2
1
⎞
⎠ ⎟
C1
between FB1 and ground and R2 is a resistor between
FB1 and the buck-boost output voltage:
V
pin should be connected to a low ESR buck-boost output
capacitor. The capacitor should be placed as close to the
IC as possible and should have a short return path to
ground.
SW1B (Pin 20): Buck-Boost Switch Node. This pin must
be connected to one side of the buck-boost inductor.
PGND1 (Pin 21): High Current Ground Connection for
the Buck-Boost NMOS Power Devices. The PCB trace
connecting this pin to ground should be made as short
and wide as possible.
SW1A (Pin 22): Buck-Boost Switch Node. This pin must
be connected to one side of the buck-boost inductor.
PV
ply Connections Used to Power the Buck-Boost Converter
Power Switch A. These pins should be connected together
and bypassed by a 22µF or larger ceramic capacitor. The
bypass capacitor should be placed as close to the pin as
possible and should have a short return path to ground.
Pins PV
together in the application circuit.
Exposed Pad (Pin 25): Ground. The Exposed Pad must be
electrically connected to ground and soldered to the PCB.
Pins PGND1, PGND2, SGND, and the Exposed Pad must
be connected together in the application circuit.
OUT1
IN1
V
OUT
(Pin 23), PV
(Pin 19): Buck-Boost Output Voltage Node. This
IN1
=
, PV
0 782
.
IN2
V
, PV
IN3
⎛
⎝ ⎜
1
(Pin 24): High Current Power Sup-
IN3
+
R
R
, and SV
2
1
⎞
⎠ ⎟
IN
must be connected
LTC3520
9
3520f