LTC3118_15 Datasheet, PDF (9/38 Pages) Linear Technology – 18V, 2A Buck-Boost DC/DC Converter with Low-Loss Dual Input PowerPath

LTC3118
Pin Functions (QFN/TSSOP)
SEL (Pin 1/Pin 4): Input Select Pin.
SEL = Logic Low (ground): V_IN1 priority mode, the con-
verter will operate from V_IN1 if RUN1 and V_IN1 voltages
are above their respective thresholds. If these conditions
are not met, the converter will operate from V_IN2 as long
as RUN2 and V_IN2 voltages are above their thresholds.
SEL = Logic High (connect to V_CC): Ideal diode mode,
the converter will operate from the higher voltage of V_IN1
or V_IN2.
V_IN1 (Pin 2/Pin 5): The first input voltage source for the
converter. Connect a minimum of 22µF ceramic decou-
pling capacitor from this pin to ground, as close to the IC
as possible. In ideal diode mode (SEL = 1), this input will
be selected if V_IN1 > V_IN2, V_IN1 is above its internal UVLO
threshold, and RUN1 > 1.22V. In priority mode (SEL =
0), this input will be selected if V_IN1 is above its internal
UVLO threshold and RUN1 > 1.22V.
Since this input has lower R_DS(ON) MOSFETs between V_IN1
and SW1, it should be considered for use with the source
where high efficiency is more critical.
RUN1 (Pin 3/Pin 6): Input to enable and disable the IC and
program the UVLO threshold for V_IN1. Pull RUN1 above
1.22V to enable the converter. Connecting this pin to a
resistor divider from V_IN1 to ground allows programming
of V_IN1’s UVLO threshold above 2.2V. Pulling both RUN1
and RUN2 to logic low states will put the IC in a low cur-
rent shutdown state.
RUN2 (Pin 4/Pin 7): Input to enable and disable the IC and
program the UVLO threshold for V_IN2. Pull RUN2 above
1.22V to enable the converter. Connecting this pin to a
resistor divider from V_IN2 to ground allows programming
of V_IN2’s UVLO threshold above 2.2V. Pulling both RUN1
and RUN2 to logic low states will put the IC in a low cur-
rent shutdown state.
V_CC (Pin 5/Pin 8): Output voltage of the internal V_CC regula-
tor. This is the supply pin for the internal driver circuitry.
Bypass this output with a 4.7µF ceramic capacitor. This
pin may be back driven by an external supply, up to 5.5V.
V_CC will be generated from either V_IN1 or V_IN2 depending
upon which input the converter is operating from.
MODE (Pin 6/Pin 9): PWM or Auto Burst Mode Select Pin.
MODE = Logic Low (ground): Enables automatic Burst
Mode operation.
MODE = Logic High (connect to V_CC): Forces PWM mode
operation.
GND (Pin 7/Pins 10, 11): Signal Ground for the IC. Provide
a short direct PCB path from this pin to the ground plane.
VC (Pin 8/Pin 12): Output of the voltage error amplifier
used to program average inductor current. An RC from
this pin to ground sets the voltage loop compensation.
The average current loop is internally compensated.
FB (Pin 9/Pin 13): Feedback input to the voltage error am-
plifier. Connect to a resistor divider from V_OUT to ground.
The output voltage can be adjusted from 2V to 18V by:
V_OUT = 1 + (R1/R2).
V1GD (Pin 10/Pin 14): Open-drain indicator that pulls to
ground when both V_IN1 and RUN1 are above their respec-
tive thresholds. Connect a pull-up resistor from this pin
to a positive supply.
V2GD (Pin 11/Pin 15): Open-drain indicator that pulls to
ground when both V_IN2 and RUN2 are above their respec-
tive thresholds. Connect a pull-up resistor from this pin
to a positive supply.
PGD (Pin 12/Pin 16): Open-drain output that pulls to
ground when V_OUT is greater than 92% of the programmed
output voltage. Connect a pull-up resistor from this pin
to a positive supply.
V_OUT (Pin 13/Pin 19): Regulated Output Voltage. Con-
nect a minimum of 47µF ceramic or low ESR decoupling
capacitor from this pin to ground. The capacitor should
be placed as close to the IC as possible with short, wide
traces to V_OUT and GND.
SW2 (Pin 14/Pin 20): Switch Pin. Connect to the other
side of the inductor. Keep PCB trace lengths as short and
wide as possible to reduce EMI.
BST2 (Pin 15/Pin 21): Bootstrapped floating supply for
high side N-channel MOSFET gate drive. Connect to SW2
through a 0.1µF capacitor, as close to the part as possible.
3118f
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