LTC3853 Datasheet, PDF (9/36 Pages) Linear Technology – Triple Output, Multiphase Synchronous Step-Down Controller

LTC3853
PIN FUNCTIONS
TG1, TG2, TG3 (Pins 32, 26, 19): Top Gate Driver Outputs.
These are the outputs of floating drivers with a voltage
swing equal to INTV_CC superimposed on the switch nodes
voltages.
BOOST1, BOOST2, BOOST3 (Pins 33, 25, 18): Boosted
Floating Driver Supplies. The (+) terminal of the booststrap
capacitors connect to these pins. These pins swing from a
diode voltage drop below INTV_CC up to V_IN + INTV_CC.
RUN1, RUN2, RUN3 (Pins 36, 35, 34): Run Control In-
puts. A voltage above 1.2V on any RUN pin turns on the
IC. However, forcing any of these pins below 1.2V causes
the IC to shut down the circuitry required for that particular
channel. There are 0.5μA pull-up currents for these pins.
Once the RUN pin rises above 1.2V, an additional 4.5μA
pull-up current is added to the pin.
MODE/PLLIN (Pin 37): Force Continuous Mode, Burst
Mode, or Pulse Skip Mode Selection Pin and External
Synchronization Input to Phase Detector Pin. Connect
this pin to SGND to force all channels into the continuous
mode of operation. Connect to INTV_CC to enable pulse
skip mode of operation. Leaving the pin floating will en-
able Burst Mode operation. A clock on the pin will force
the controller into continuous mode of operation and
synchronize the internal oscillator.
FREQ/PLLFLTR (Pin 38): The phase-locked loop’s low-
pass filter is tied to this pin. Alternatively, this pin can
be driven with a DC voltage to vary the frequency of the
internal oscillator.
I_LIM (Pin 39): Current Comparator Sense Voltage Range
Inputs. This pin is to be programmed to SGND, FLOAT or
INTV_CC to set the maximum current sense threshold to
three different levels.
TK/SS1, TK/SS2, TK/SS3 (Pins 40, 1, 2): Output Voltage
Tracking and Soft-Start Inputs. When one particular channel
is configured to be the master, a capacitor to ground at
this pin sets the ramp rate for the master channel’s output
voltage. When the channel is configured to be the slave,
the V_FB voltage of the master channel is reproduced by a
resistor divider and applied to this pin. Internal soft-start
currents of 1.3μA are charging the soft-start capacitors.
In dual output (2 + 1) mode, TK/SS1 and TK/SS2 need to
be shorted externally.
Exposed Pad (Pin 41): Power Ground. Connect these pins
closely to the sources of the bottom N-channel MOSFETs,
the (–) terminal of C_VCC and the (–) terminal of C_IN.
3853f
9