LTC3890
pin FuncTions
–
–
SGND(Pins6, ExposedPadPin33):Small-signalground
common to both controllers, must be routed separately
from high current grounds to the common (–) terminals
SENSE1 , SENSE2 (Pin 1, Pin 9): The (–) Input to the
Differential Current Comparators. When greater than
–
INTV – 0.5V, the SENSE pin supplies current to the
CC
of the C capacitors. The exposed pad must be soldered
current comparator.
IN
to PCB ground for rated thermal performance.
FREQ (Pin 2): The frequency control pin for the internal
RUN1, RUN2 (Pin 7, Pin 8): Digital Run Control Inputs
for Each Controller. Forcing RUN1 below 1.16V or RUN2
below 1.20V shuts down that controller. Forcing both of
these pins below 0.7V shuts down the entire LTC3890,
reducing quiescent current to approximately 14µA.
VCO. Connecting the pin to GND forces the VCO to a fixed
low frequency of 350kHz. Connecting the pin to INTV
CC
forces the VCO to a fixed high frequency of 535kHz.
Other frequencies between 50kHz and 900kHz can be
programmed using a resistor between FREQ and GND.
An internal 20µA pull-up current develops the voltage to
be used by the VCO to control the frequency.
INTV (Pin19):OutputoftheInternalLinearLowDropout
CC
Regulator.Thedriverandcontrolcircuitsarepoweredfrom
this voltage source. Must be decoupled to power ground
with a minimum of 4.7µF ceramic or other low ESR ca-
PHASMD (Pin 3): Control Input to Phase Selector which
determines the phase relationships between control-
ler 1, controller 2 and the CLKOUT signal. Pulling this
pin to ground forces TG2 and CLKOUT to be out of phase
180° and 60° with respect to TG1. Connecting this pin to
pacitor. Do not use the INTV pin for any other purpose.
CC
EXTV (Pin 20): External Power Input to an Internal LDO
CC
Connected to INTV . This LDO supplies INTV power,
CC
CC
INTV forces TG2 and CLKOUT to be out of phase 240°
CC
bypassing the internal LDO powered from V whenever
IN
and 120° with respect to TG1. Floating this pin forces TG2
and CLKOUT to be out of phase 180° and 90° with respect
to TG1. Refer to Table 1.
EXTV is higher than 4.7V. See EXTV Connection in the
CC
CC
Applications Information section. Do not float or exceed
14V on this pin.
CLKOUT (Pin 4): Output clock signal available to daisy-
PGND (Pin 21): Driver Power Ground. Connects to the
chain other controller ICs for additional MOSFET driver
sources of bottom (synchronous) N-channel MOSFETs
stages/phases. The output levels swing from INTV to
CC
and the (–) terminal(s) of C .
IN
ground.
V (Pin 22): Main Supply Pin. A bypass capacitor should
IN
PLLIN/MODE (Pin 5): External Synchronization Input to
PhaseDetectorandForcedContinuousModeInput. When
an external clock is applied to this pin, the phase-locked
loop will force the rising TG1 signal to be synchronized
with the rising edge of the external clock. When not syn-
chronizing to an external clock, this input, which acts on
bothcontrollers, determineshowtheLTC3890operatesat
light loads. Pulling this pin to ground selects Burst Mode
operation.Aninternal100kresistortogroundalsoinvokes
BurstModeoperationwhenthepinisfloated.Tyingthispin
be tied between this pin and the signal ground pin.
BG1, BG2 (Pin 23, Pin 18): High Current Gate Drives
for Bottom (Synchronous) N-Channel MOSFETs. Voltage
swing at these pins is from ground to INTV .
CC
BOOST1,BOOST2(Pin24,Pin17):BootstrappedSupplies
to the Topside Floating Drivers. Capacitors are connected
between the BOOST and SW pins and Schottky diodes are
tied between the BOOST and INTV pins. Voltage swing
CC
at the BOOST pins is from INTV to (V + INTV ).
CC
IN
CC
to INTV forces continuous inductor current operation.
CC
SW1, SW2 (Pin 25, Pin 16): Switch Node Connections
to Inductors.
Tying this pin to a voltage greater than 1.2V and less than
INTV – 1.3V selects pulse-skipping operation.
CC
3890fb
8
Linear Systems [ Linear Systems ]
