Datasheet

LTC3112
9
3112fc
For more information www.linear.com/LTC3112
pin FuncTions
COMP (Pin 1/Pin 2): Error Amp Output. An R-C network
connected from this pin to FB sets the loop compensation
for the voltage converter.
FB (Pin 2/Pin 3): Feedback Voltage Input. Connect V
OUT
resistor divider tap to this pin. The output voltage can
be adjusted from 2.5V to 14V by the following equation:
V
OUT
= 0.8V • 1+
R1
R2






where R1 is the resistor between V
OUT
and FB and R2 is
the resistor between FB and GND.
OVP (Pin 3/Pin 4): Overvoltage Protection Input. The
common point of a resistor divider between V
OUT
and GND
can also be used to program the overvoltage protection
to a lower voltage by the following equation:
V
OVP
= 0.83V• 1+
R3
R4






where R3 is the resistor between V
OUT
and OVP and R4
is the resistor between OVP and GND.
V
IN
(Pins 4, 5/Pins 5, 6): Input Supply Voltage. This pin
should be bypassed to the ground plane with at least
10µF of low ESR, low ESL ceramic capacitance. Place this
capacitor as close to the pin as possible and have as short
a return path to the ground plane as possible.
RUN (Pin 6/Pin 7): Shutdown Control Input. Operation
will be disabled when the voltage is forced below 0.75V
(typical) and less than 1µA of quiescent current will be
consumed.
I
OUT
(Pin 7/Pin 8): A Current approximately 24µA/A of
the D Switch Output Current is Sourced from this Pin.
An R-C circuit can be used to control the average output
current or provide an analog output current monitor (see
Applications Information section).
V
OUT
(Pin 8/Pin 9): Regulated Output Voltage. This pin
should be connected to a low ESR ceramic capacitor of at
least 47µF. The capacitor should be placed as close to the
pin as possible and have a short return to the ground plane.
SW2 (Pins 9, 10/Pins 12, 13): Internal switches C and D
and the external inductor are
connected here.
BST2 (
Pin 11/Pin 14): Boosted Floating Driver Supply
for D-Switch Driver. Connect a 0.1µF capacitor from this
pin to SW2.
SW1 (Pins 12, 13/Pins 15, 16): Internal switches A and
B and the external inductor are connected here.
BST1 (Pin 14/Pin 17): Boosted Floating Driver Supply
for A-Switch Driver. Connect a 0.1µF capacitor from this
pin to SW1.
V
CC
(Pin 15/Pin 18): External Capacitor Connection for
the Regulated V
CC
Supply. This supply is used to operate
internal circuitry and switch drivers. V
CC
will track V
IN
up
to 4.2V, but will maintain this voltage when V
IN
> 4.2V.
Connect a 1µF ceramic capacitor from this pin to GND.
PWM/SYNC (Pin 16/Pin 19): Burst Mode Control and Syn
-
chronization Input. A DC voltage <0.5V commands Burst
Mode operation, >1.5V commands 750kHz fixed frequency
mode. A digital pulse train between 300kHz and 1500kHz
applied to this pin will override the internal oscillator and
set the operating frequency. The pulse train should have
minimum high or low times greater than 100ns (Note 7).
Note the LTC3112 has reduced power capability when
operating in Burst Mode operation. Refer to the Operation
section of this data sheet for details.
GND (Exposed Pad Pin 17/Pins
1, 10, 11, 20, Exposed
Pad Pin 21): Ground. Small-Signal and Power Ground
for the IC. The exposed pad must be soldered to the PCB
and electrically connected to ground through the shortest
and lowest impedance connection possible. The bulk of
the heat flow is through this pad, so printed circuit board
design has an impact on the thermal performance of the
IC. See PCB Layout and Thermal Considerations sections
for more details.
(DFN/TSSOP)