Datasheet

LTC3853
8
3853fa
PIN FUNCTIONS
SENSE1
+
, SENSE2
+
, SENSE3
+
(Pins 3, 5, 7): Current Sense
Comparator Inputs. The (+) inputs to the current compara-
tors are normally connected to DCR sensing networks or
current sensing resistors. SENSE3
+
common modes up
to 13.5V, allowing higher V
OUT
voltages on channel 3.
SENSE1
–
, SENSE2
–
, SENSE3
–
(Pins 4, 6, 8): Current
Sense Comparator Inputs. The (–) inputs to the current
comparators are connected to the outputs. SENSE3
–
com-
mon modes up to 13.5V, allowing higher V
OUT
voltages
on channel 3.
V
FB1
, V
FB2
, V
FB3
(Pins 9, 12, 14): Error Amplifier Feedback
Inputs. These pins receive the remotely sensed feedback
voltages for each channel from external resistive dividers
across the outputs. Connecting V
FB2
to V
IN
through a 200k
resistor enables dual output (2 + 1) mode.
I
TH1
, I
TH2
, I
TH3
(Pins 10, 13, 15): Current Control Thresh-
olds and Error Amplifier Compensation Points. Each as-
sociated channels’ current comparator tripping threshold
increases with its I
TH
control voltage. In dual output (2 +
1) mode, I
TH1
and I
TH2
need to be shorted externally.
SGND (Pin 11): Signal Ground. All small-signal compo-
nents and compensation components should connect
to this ground, which in turn connects to PGND at one
point.
PGOOD3 (Pin 16): Power Good Indicator Output for Phase
3. Open-drain logic out that is pulled to ground when any
channel output exceeds the ±7.5% regulation window, after
the internal 17µs power bad mask timer expires.
PGOOD12 (Pin 17): Power Good Indicator Output for
Phases 1 and 2. Open-drain logic out that is pulled to
ground when any channel output exceeds the ±7.5%
regulation window, after the internal 17µs power bad
mask timer expires.
INTV
CC
(Pin 22): Internal 5V Regulator Output. The
control circuits are powered from this voltage. Also
provides channel 3 driver power. Decouple this pin to
PGND with a minimum of 4.7µF low ESR tantalum or
ceramic capacitor.
EXTV
CC
(Pin 23): External Power Input to an Internal Switch
Connected to INTV
CC
. This switch closes and supplies the
IC power, bypassing the internal low dropout regulator,
whenever EXTV
CC
is higher than 4.7V. Do not exceed 6V
on this pin and ensure V
IN
> V
EXTVCC
at all times.
V
IN
(Pin 24): Main Input Supply. Decouple this pin to
PGND with a capacitor (0.1µF to 1µF).
DRV
CC12
(Pin 29): Driver Voltage Input for Channels 1 and
2. Do not exceed 6V on this pin. This pin must be tied to
INTV
CC
externally.
BG1, BG2, BG3 (Pins 30, 28, 21): Bottom Gate Driver
Outputs. These pins drive the gates of the bottom N-channel
MOSFETs between PGND and INTV
CC
/DRV
CC12
.
SW1, SW2, SW3 (Pins 31, 27, 20): Switch Node Con-
nections to Inductors. Voltage swing at these pins is from
a Schottky diode (external) voltage drop below ground
to V
IN
.