Datasheet LTC3520 (Analog Devices) - 9

LTC3520
PIN FUNCTIONS SS2 (Pin 13):
Buck Converter Soft-Start Pin. This pin must between FB1 and ground and R2 is a resistor between be connected to a soft-start capacitor. The value of the FB1 and the buck-boost output voltage: capacitor determines the duration of the soft-start period. ⎛ R2⎞ For information on choosing the value of this capacitor, see V 0.782V OUT = 1+ the Applications Information section of this datasheet. ⎝⎜ 1⎠⎟ R
FB2 (Pin 14):
Feedback Voltage for the Buck Converter.
VOUT1 (Pin 19):
Buck-Boost Output Voltage Node. This This pin is derived from a resistor divider on the buck pin should be connected to a low ESR buck-boost output output voltage. The buck output voltage is given by the capacitor. The capacitor should be placed as close to the following equation where R1 is a resistor between FB2 IC as possible and should have a short return path to and ground and R2 is a resistor between FB2 and the ground. buck output voltage:
SW1B (Pin 20):
Buck-Boost Switch Node. This pin must ⎛ R2⎞ V 0.790V be connected to one side of the buck-boost inductor. OUT = 1+ ⎝⎜ 1⎠⎟ R
PGND1 (Pin 21):
High Current Ground Connection for
V
the Buck-Boost NMOS Power Devices. The PCB trace
C1 (Pin 15):
Buck-Boost Error Amplifi er Output. A fre- quency compensation network is connected to FB1 to connecting this pin to ground should be made as short compensate the loop. During Burst Mode operation, V and wide as possible. C1 is driven internally by a clamp circuit.
SW1A (Pin 22):
Buck-Boost Switch Node. This pin must
SGND (Pin 16):
Small Signal Ground. This pin is used be connected to one side of the buck-boost inductor. as a ground reference for the internal circuitry of the
PVIN1 (Pin 23), PVIN3 (Pin 24):
High Current Power Sup- LTC3520. ply Connections Used to Power the Buck-Boost Converter
SS1 (Pin 17):
Buck-Boost Converter Soft-Start Pin. This Power Switch A. These pins should be connected together pin must be connected to a soft-start capacitor. The value and bypassed by a 22μF or larger ceramic capacitor. The of the capacitor determines the duration of the soft-start bypass capacitor should be placed as close to the pin as period. For information on choosing the value of this possible and should have a short return path to ground. capacitor, see the Applications Information section of
Pins PVIN1, PVIN2, PVIN3, and SVIN must be connected
this datasheet.
together in the application circuit. FB1 (Pin 18):
Feedback Voltage for the Buck-Boost Con-
Exposed Pad (Pin 25):
Ground. The Exposed Pad must be verter. This pin is derived from a resistor divider on the electrically connected to ground and soldered to the PCB. buck-boost output voltage. The buck-boost output voltage
Pins PGND1, PGND2, SGND, and the Exposed Pad must
is given by the following equation where R1 is a resistor
be connected together in the application circuit.
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