LTC3613
8
3613fa
PIN FUNCTIONS
PV
IN
(Pins 1-9, 53-56, 57 Exposed Pad): Power Supply
Inputs. These pins connect to the drain of the internal
power MOSFETS. The PV
IN
exposed pad must be soldered
to the circuit board for electrical contact and rated thermal
performance. The supply voltage can range from 4.5V to
24V. The voltage on this pin is also used to adjust the TG
on-time in order to maintain constant frequency operation.
SW (Pins 10, 35, 45-51, 58 Exposed Pad): Switch Node
Connection. The (–) terminal of the bootstrap capacitor,
C
B
, connects to this node. This pin swings from a diode
voltage below ground up to V
IN
. The SW exposed pad must
be soldered to the circuit board for electrical contact and
rated thermal performance.
BOOST (Pin 11): Boosted Driver Supply Connection. The
(+) terminal of the bootstrap capacitor, C
B
, as well as
the cathode of the Schottky diode, D
B
, connects to this
node. This node swings from INTV
CC
– V
SCHOTTKY
to V
IN
+ INTV
CC
– V
SCHOTTKY
.
SGND (Pins 12, 16, 17, 19, 28, 29, 59 Exposed Pad):
Signal Ground Connection. The SGND exposed pad must
be soldered to the circuit board for electrical contact and
rated thermal performance. All small-signal components
should be connected to the signal ground. Connect signal
ground to power ground only at one point using a single
PCB trace.
PGOOD (Pin 13): Power Good Indicator Output. This
open-drain logic output is pulled to ground when the
output voltage is outside of a ±7.5% window around the
regulation point.
SENSE
+
(Pin 14): Differential Current Sensing (+) Input.
For R
SENSE
current sensing, Kelvin (4-wire) connect
SENSE
+
and SENSE
–
pins across the sense resistor. For
DCR sensing, Kelvin connect SENSE
+
and SENSE
–
pins
across the sense filter capacitor.
SENSE
–
(Pin 15): Differential Current Sensing (–) Input.
For R
SENSE
current sensing, Kelvin (4-wire) connect the
SENSE
+
and SENSE
–
pins across the sense resistor. For
DCR sensing, Kelvin connect the SENSE
+
and SENSE
–
pins
across the sense filter capacitor.
V
OUT
(Pin 18): Output voltage sense for adjusting the
on-time for constant frequency operation. Tying this pin to
the local output (instead of the remote output) is recom-
mended for most applications. This pin can be programmed
as needed for achieving the steady-state on-time required
for constant frequency operation.
V
OSNS
–
(Pin 20): Differential Output Sensing (–) Input.
Connect this pin to the negative terminal of the output
capacitor. There is a bias current of 35µA (typical) flowing
out of this pin.
V
OSNS
+
(Pin 21): Differential Output Sensing (+) Input.
Connect this pin to the feedback resistor divider between
the positive and negative output capacitor terminals. In
normal operation the LTC3613 will regulate the differen-
tial output voltage which is divided down to 0.6V by the
feedback resistor divider.
TRACK/SS (Pin 22): External Tracking and Soft-Start Input.
The LTC3613 regulates the differential feedback voltage
(V
OSNS
+
− V
OSNS
–
) to the smaller of 0.6V or the voltage
on the TRACK/SS pin. An internal 1.0A pull-up current
source is connected to this pin. A capacitor to ground at
this pin sets the ramp time to the final regulated output
voltage. Alternatively, another voltage supply connected
through a resistor divider to this pin allows the output to
track the other supply during start-up.
ITH (Pin 23): Current Control Voltage and Switching Regu-
lator Compensation Point. The current sense threshold
increases with this control voltage which ranges from
0V to 2.4V.
V
RNG
(Pin 24): Current Sense Voltage Range Input. The
maximum allowed sense voltage between SENSE
+
and
SENSE
–
is equal to 0.05 • V
RNG
. If V
RNG
is tied to SGND,
the device operates with a maximum sense voltage of
30mV. If V
RNG
is tied to INTV
CC
, the device operates with
a maximum sense voltage of 50mV.
RT (Pin 25): Switching Frequency Programming Pin.
Connect an external resistor from RT to signal ground to
program the switching frequency between 200kHz and
1MHz. An external clock applied to MODE/PLLIN must
be within ±30% of this free-running frequency to ensure
frequency lock.
