Datasheet LTC3520 (Analog Devices) - 8

LTC3520
PIN FUNCTIONS SVIN (Pin 1):
Small Signal Power Supply Connection. amplifi er. Forcing this pin below 0.4V disables the uncom- This pin is used to power the internal circuitry of the mitted amplifi er. This pin cannot be left fl oating. LTC3520. This pin should be bypassed using a 0.1μF or
PV
larger ceramic capacitor placed as close as possible to
IN2 (Pin 9):
High Current Power Supply Connection Used to Supply the Buck Converter PMOS Power Device. the pin with a short return path to ground.
Pins PVIN1,
This pin should be bypassed by a 22μF or larger ceramic
PVIN2, PVIN3, and SVIN must be connected together in
capacitor. The bypass capacitor should be placed as close
the application circuit.
to the pin as possible and should have a short return path
AOUT (Pin 2):
Uncommitted Amplifi er Output. This pin to ground.
Pins PVIN1, PVIN2, PVIN3, and SVIN must be
should be connected to the base of an external PNP
connected together in the application circuit.
transistor for use as an LDO regulator. If used as a
SW2 (Pin 10):
Buck Converter Switch Node. This pin must battery-good indicator or for supply sequencing, this pin be connected to one side of the buck inductor. is the comparator output.
PGND2 (Pin 11):
High Current Ground Connection for the
AIN (Pin 3):
Non-Inverting Input to the Uncommitted Buck Converter N-Channel MOSFET Power Device. The Amplifi er. In LDO applications, this pin is connected to PCB trace connecting this pin to ground should be made the LDO feedback voltage. as short and wide as possible.
RT (Pin 4):
Programs the Frequency of the Internal Oscilla-
PWM2 (Pin 12):
Burst/PWM Mode Control Pin for the Buck tor. This pin must be tied to ground via an external resistor. Converter. This pin can be used in the following ways: The value of the resistor controls the oscillator frequency. For details on choosing the value of this resistor see the PWM2 forced high: With PWM2 forced high, the buck Applications Information section of this datasheet. converter will be forced into low noise fi xed frequency operation. The buck converter will remain in this mode
PWM1 (Pin 5):
Logic Input Used to Choose Between Burst unless the load current is low enough that the minimum and PWM Mode for the Buck-Boost Converter. This pin on-time is reached at which point the converter will cannot be left fl oating. begin pulse-skipping to maintain regulation. PWM1 = Low: The buck-boost converter will operate in PWM2 connected to ground via resistor: PWM2 can be variable frequency mode to improve effi ciency at light connected to ground through a resistor to control the loads. In this mode, the LTC3520 can only supply a load current at which Burst Mode operation is entered reduced load current (typically 50mA). and exited. Larger resistor values will cause the buck PWM1 = High: The buck-boost converter will remain converter to enter Burst Mode operation at lower load in low noise, fi xed frequency PWM mode at all load currents and will result in lower output voltage ripple currents. in Burst Mode operation. Smaller resistor values will
SD1
cause Burst Mode operation to be entered at higher load
(Pin 6):
Buck-Boost Active-Low Shutdown Pin. Forc- currents and the Burst Mode ripple will be larger. ing this pin above 1.4V enables the buck-boost converter. Forcing this pin below 0.4V disables the buck-boost PWM2 forced low: With PWM2 forced to ground, the converter. This pin cannot be left fl oating. buck converter will operate in Burst Mode operation for
SD2
all but the highest load currents. Generally, this mode of
(Pin 7):
Buck Active-Low Shutdown Pin. Forcing operation is utilized to force the buck converter into Burst this pin above 1.4V enables the buck converter. Forcing Mode operation when it is known that the load current this pin below 0.4V disables the buck converter. This pin will be relatively low (under 75mA) or in applications cannot be left fl oating. that are not sensitive to output voltage ripple.
SD3 (Pin 8):
Uncommitted Amplifi er Active-Low Shutdown Pin. Forcing this pin above 1.4V enables the uncommitted 3520fa 8