LTC3522_15 Datasheet, PDF (6/20 Pages) Linear Technology – Synchronous 400mA Buck-Boost and 200mA Buck Converters

LTC3522
PIN FUNCTIONS
FB2 (Pin 1): Feedback Voltage for the Buck Converter De-
rived 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_OUT
=
0.594V ^{⎛⎝⎜}1+
R2⎞
R1⎠⎟
PWM (Pin 2): Logic Input Used to Choose Between Burst
and PWM Mode Operation for Both Converters. This pin
cannot be left floating.
PWM = Low: Burst Mode operation is enabled on both
converters. The buck converter will operate in Burst
Mode operation at light current but will automatically
transition to PWM operation at higher currents. The
buck converter can supply its maximum output current
(200mA) in this mode. The buck-boost converter will
operate in variable frequency mode and can only supply
a reduced load current (typically 50mA).
PWM = High: Both converters are forced into low noise
1MHz PWM mode operation. The buck converter will
remain at constant frequency operation until its mini-
mum on-time is reached. The buck-boost converter will
remain in PWM mode at all load currents.
GND (Pin 3): Small-Signal Ground Used as a Ground
Reference for the Internal Circuitry of the LTC3522.
PGOOD2 (Pin 4): This pin is an open-drain output which
will only pull low if the buck converter is enabled and one
or more of the following conditions occurs: the buck output
voltage is out of regulation, the part is in overtemperature
shutdown or the part is in undervoltage lockout.
FB1 (Pin 5): Feedback Voltage for the Buck-Boost Con-
verter 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 between
FB1 and ground and R2 is a resistor between FB1 and the
buck-boost output voltage:
V_OUT
=
1V ^{⎛⎝⎜}1+
R2⎞
R1⎠⎟
PGOOD1 (Pin 6): This pin is an open-drain output which
will only pull low if the buck-boost converter is enabled
and one or more of the following conditions occurs: the
buck-boost output voltage is out of regulation, the part is
in overtemperature shutdown, the part is in undervoltage
lockout or the buck-boost converter is in current limit. See
the Operation section of this data sheet for details on the
functionality of this pin in PWM mode.
SHDN1 (Pin 7): Buck-Boost Active-Low Shutdown Pin.
Forcing this pin above 1.4V enables the buck-boost con-
verter. Forcing this pin below 0.4V disables the buck-boost
converter. This pin cannot be left floating.
PV_IN1 (Pin 8): High Current Power Supply Connection Used
to Supply Switch A of the Buck-Boost Converter. This pin
should be bypassed by a 4.7μF 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_IN1 and PV_IN2 must be connected together in the
application circuit.
PGND2 (Pin 9): High Current Ground Connection for the
Buck-Boost Switch C. The PCB trace connecting this pin to
ground should be made as short and wide as possible.
3522fa
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