LTC3115-1
11
Rev. C
PIN FUNCTIONS
(DHD/FE)
RUN (Pin 1/Pin 2):
Input to Enable and Disable the IC and
Set Custom Input UVLO Thresholds. The RUN pin can be
driven by an external logic signal to enable and disable
the IC. In addition, the voltage on this pin can be set by
a resistor divider connected to the input voltage in order
to provide an accurate undervoltage lockout threshold.
The IC is enabled if RUN exceeds 1.21V nominally. Once
enabled, a 0.5µA current is sourced by the RUN pin to pro-
vide hysteresis. To continuously enable the IC, this pin can
be tied directly to the input voltage. The RUN pin cannot
be forced more than 0.3V above V
IN
under any condition.
SW2 (Pin 2/Pin 3):
Buck-Boost Converter Power Switch
Pin. This pin should be connected to one side of the buck-
boost inductor.
PV
OUT
(Pin 3/Pin 4):
Buck-Boost Converter Power Output.
This pin should be connected to a low ESR capacitor with
a value of at least 10µF. The capacitor should be placed as
close to the IC as possible and should have a short return
path to ground. In applications with V
OUT
> 20V that are
subject to output overload or short-circuit conditions, it
is recommended that a Schottky diode be installed from
SW2 (anode) to PV
OUT
(cathode). In applications subject
to output short circuits through an inductive load, it is rec-
ommended that a Schottky diode be installed from ground
(anode) to PV
OUT
(cathode) to limit the extent that PV
OUT
is driven below ground during the short-circuit transient.
GND (Pins 4, 5/Pins 5, 6):
Signal Ground. These pins are
the ground connections for the control circuitry of the IC
and must be tied to ground in the application.
VC (Pin 6/Pin 7):
Error Amplifier Output. A frequency
compensation network must be connected between this
pin and FB to stabilize the voltage control loop.
FB (Pin 7/Pin 8):
Feedback Voltage Input. A resistor
divider connected to this pin sets the output voltage
for the buck-boost converter. The nominal FB voltage is
1000mV. Care should be taken in the routing of connec-
tions to this pin in order to minimize stray coupling to the
switch pin traces.
RT (Pin 8/Pin 9):
Oscillator Frequency Programming Pin.
A resistor placed between this pin and ground sets the
switching frequency of the buck-boost converter.
V
CC
(Pin 9/Pin 12):
Low Voltage Supply Input for IC
Control Circuitry. This pin powers internal IC control cir-
cuitry and must be connected to the PV
CC
pin in the appli-
cation. A 4.7µF or larger bypass capacitor should be con-
nected between this pin and ground.
The V
CC
and PV
CC
pins must be connected together in the application.
V
IN
(Pin 10/Pin 13):
Power Supply Connection for Internal
Circuitry and the V
CC
Regulator. This pin provides power
to the internal V
CC
regulator and is the input voltage sense
connection for the V
IN
divider. A 0.1µF bypass capacitor
should be connected between this pin and ground. The
bypass capacitor should be located as close to the IC as
possible and should have a short return path to ground.
PV
CC
(Pin 11/Pin 14):
Internal V
CC
Regulator Output. This
pin is the output pin of the internal linear regulator that
generates the V
CC
rail from V
IN
. The PV
CC
pin is also the
supply connection for the power switch gate drivers. If
the trace connecting PV
CC
to V
CC
cannot be made short
in length, an additional bypass capacitor should be con-
nected between this pin and ground.
The V
CC
and PV
CC
pins must be connected together in the application.
BST2 (Pin 12/Pin 15):
Flying Capacitor Pin for SW2. This
pin must be connected to SW2 through a 0.1µF capacitor.
This pin is used to generate the gate drive rail for power
switch D.
BST1 (Pin 13/Pin 16):
Flying Capacitor Pin for SW1. This
pin must be connected to SW1 through a 0.1µF capacitor.
This pin is used to generate the gate drive rail for power
switch A.
PV
IN
(Pin 14/Pin 17):
Power Input for the Buck-Boost
Converter. A 4.7µF or larger bypass capacitor should
be connected between this pin and ground. The bypass
capacitor should be located as close to the IC as possible
and should via directly down to the ground plane. When
powered through long leads or from a high ESR power
source, a larger bulk input capacitor (typically 47µF to
100µF) may be required.
SW1 (Pin 15/Pin 18):
Buck-Boost Converter Power
Switch Pin. This pin should be connected to one side of
the buck-boost inductor.
