Datasheet LTC3522 (Analog Devices) - 6

LTC3522
PIN FUNCTIONS FB2 (Pin 1):
Feedback Voltage for the Buck Converter De-
FB1 (Pin 5):
Feedback Voltage for the Buck-Boost Con- rived from a Resistor Divider on the Buck Output Voltage. verter Derived from a Resistor Divider on the Buck-Boost The buck output voltage is given by the following equation Output Voltage. The buck-boost output voltage is given where R1 is a resistor between FB2 and ground and R2 is by the following equation where R1 is a resistor between a resistor between FB2 and the buck output voltage: FB1 and ground and R2 is a resistor between FB1 and the ⎛ buck-boost output voltage: R ⎞ 2 V 0 594 . V OUT = 1+ ⎝⎜ R ⎠⎟ 1 ⎛ R ⎞ 2 V V OUT = 1 1+ ⎝⎜ R ⎠⎟ 1
PWM (Pin 2):
Logic Input Used to Choose Between Burst and PWM Mode Operation for Both Converters. This pin
PGOOD1 (Pin 6):
This pin is an open-drain output which cannot be left fl oating. will only pull low if the buck-boost converter is enabled and one or more of the following conditions occurs: the PWM = Low: Burst Mode operation is enabled on both buck-boost output voltage is out of regulation, the part is converters. The buck converter will operate in Burst in overtemperature shutdown, the part is in undervoltage Mode operation at light current but will automatically lockout or the buck-boost converter is in current limit. See transition to PWM operation at higher currents. The the Operation section of this data sheet for details on the buck converter can supply its maximum output current functionality of this pin in PWM mode. (200mA) in this mode. The buck-boost converter will operate in variable frequency mode and can only supply
SHDN1 (Pin 7):
Buck-Boost Active-Low Shutdown Pin. a reduced load current (typically 50mA). Forcing this pin above 1.4V enables the buck-boost con- verter. Forcing this pin below 0.4V disables the buck-boost PWM = High: Both converters are forced into low noise converter. This pin cannot be left fl oating. 1MHz PWM mode operation. The buck converter will remain at constant frequency operation until its mini-
PVIN1 (Pin 8):
High Current Power Supply Connection Used mum on-time is reached. The buck-boost converter will to Supply Switch A of the Buck-Boost Converter. This pin remain in PWM mode at all load currents. should be bypassed by a 4.7μF or larger ceramic capacitor. The bypass capacitor should be placed as close to the pin
GND (Pin 3):
Small-Signal Ground Used as a Ground as possible and should have a short return path to ground. Reference for the Internal Circuitry of the LTC3522.
Pins PVIN1 and PVIN2 must be connected together in the PGOOD2 (Pin 4):
This pin is an open-drain output which
application circuit.
will only pull low if the buck converter is enabled and one
PGND2 (Pin 9):
High Current Ground Connection for the or more of the following conditions occurs: the buck output Buck-Boost Switch C. The PCB trace connecting this pin to voltage is out of regulation, the part is in overtemperature ground should be made as short and wide as possible. shutdown or the part is in undervoltage lockout. 3522fa 6