LTC3609
8
3609fb
pin FuncTions
PV
IN
(Pins 1, 2, 3, 4, 5, 6, 7, 48, 49, 50, 51, 52, 53):
Main Input Supply. Decouple this pin to power PGND with
the input capacitance, C
IN
.
SW (Pins 8, 33, 41, 42, 43, 44, 45, 46, 47, 55): Switch
Node Connection to the Inductor. The (–) terminal of the
bootstrap capacitor, C
B
, also connects here. This pin swings
from a diode voltage drop below ground up to V
IN
.
NC (Pins 9, 21, 24, 25, 28): No Connection.
SGND (Pins
10, 14, 15, 20, 26, 27, 54): Signal Ground. All
small-signal components and compensation components
should connect to this ground, which in turn connects to
PGND at one point.
BOOST
(Pin
11): Boosted Floating Driver Supply. The (+)
terminal of the bootstrap capacitor, C
B
, connects here.
This pin swings from a diode voltage drop below INTV
CC
up to V
IN
+ INTV
CC
.
RUN/SS (Pin 12): Run Control and Soft-Start Input. A
capacitor to ground at this pin sets the ramp time to full
output current (approximately 3s/µF) and the time delay
for overcurrent latchoff (see Applications Information).
Forcing this pin below 0.8V shuts down the device.
V
ON
(Pin 13): On-Time Voltage Input. Voltage trip point for
the on-time comparator. Tying this pin to the output volt-
age or an external resistive divider from the output makes
the on-time proportional to V
OUT
. The comparator input
defaults to 0.7V when the pin is grounded and defaults to
2.4V when the pin is tied to INTV
CC
. Tie this pin to INTV
CC
in high V
OUT
applications to use a lower R
ON
value.
PGOOD (Pin 16): Power Good Output. Open-drain logic
output that is pulled to ground when the output voltage
is not within ±10% of the regulation point.
V
RNG
(Pin 17): Current Limit Range Input. The voltage at
this pin adjusts maximum valley current and can be set
from 0.7V to 1.2V by a resistive divider from INTV
CC
. It
defaults to 0.7V if the V
RNG
pin is tied to ground which
results in a typical 9A current limit.
I
TH
(Pin 18): Current Control Threshold and Error Amplifier
Compensation Point. The current comparator threshold
increases with this control voltage. The voltage ranges
from 0V to 2.4V with 0.8V corresponding to zero sense
voltage (zero current).
FCB
(Pin
19): Forced Continuous Input. Tie this pin to
ground to force continuous synchronous operation at low
load, to INTV
CC
to enable discontinuous mode operation at
low load or to a resistive divider from a secondary output
when using a secondary winding.
I
ON
(Pin 22): On-Time Current Input. Tie a resistor from V
IN
to this pin to set the one-shot timer current and thereby
set the switching frequency.
V
FB
(Pin 23): Error Amplifier Feedback Input. This pin
connects the error amplifier input to an external resistive
divider from V
OUT
.
EXTV
CC
(Pin 29): External V
CC
Input. When EXTV
CC
exceeds
4.7V, an internal switch connects this pin to INTV
CC
and
shuts down the internal regulator so that controller and
gate drive power is drawn from EXTV
CC
. Do not exceed
7V at this pin and ensure that EXTV
CC
< V
IN
.
SV
IN
(Pin 30): Supply Pin for Internal PWM Controller.
INTV
CC
(Pins 31, 32): Internal 5V Regulator Output. The
driver and control circuits are powered from this voltage.
Decouple this pin to power ground with a minimum of
4.7µF low ESR tantalum or ceramic capacitor.
PGND
(Pins 34, 35, 36, 37, 38, 39, 40): Power Ground.
Connect this pin closely to the (–) terminal of C
VCC
and
the (–) terminal of C
IN
.
