ltc3890 Linear Technology Corporation, ltc3890 Datasheet - Page 8

• Manufacturer Part Number: ltc3890
• Description: 60v Low Iq, Dual, 2-phase Synchronous Step-down Dc/dc Controller
• Manufacturer: Linear Technology Corporation

PIN FUNCTIONS
LTC3890
SENSE1
Differential Current Comparators. When greater than
INTV
current comparator.
FREQ (Pin 2): The frequency control pin for the internal
VCO. Connecting the pin to GND forces the VCO to a fi xed
low frequency of 350kHz. Connecting the pin to INTV
forces the VCO to a fi xed 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.
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
INTV
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.
CLKOUT (Pin 4): Output clock signal available to daisy-
chain other controller ICs for additional MOSFET driver
stages/phases. The output levels swing from INTV
ground.
PLLIN/MODE (Pin 5): External Synchronization Input to
Phase Detector and Forced Continuous Mode Input. 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
both controllers, determines how the LTC3890 operates at
light loads. Pulling this pin to ground selects Burst Mode
operation. An internal 100k resistor to ground also invokes
Burst Mode operation when the pin is fl oated. Tying this pin
to INTV
Tying this pin to a voltage greater than 1.2V and less than
INTV
8
CC
CC
CC
CC
forces TG2 and CLKOUT to be out of phase 240°
– 1.3V selects pulse skipping operation.
– 0.5V, the SENSE
–
, SENSE2
forces continuous inductor current operation.
–
(Pin 1, Pin 9): The (–) Input to the
–
pin supplies current to the
CC
CC
to
SGND (Pins 6, Exposed Pad Pin 33): Small-signal ground
common to both controllers, must be routed separately
from high current grounds to the common (–) terminals
of the C
RUN1, RUN2 (Pin 7, Pin 8): Digital Run Control Inputs
for Each Controller. Forcing either of these pins below
1.2V shuts down that controller. Forcing both of these
pins below 0.7V shuts down the entire LTC3890, reducing
quiescent current to approximately 14μA.
INTV
Regulator. The driver and control circuits are powered
from this voltage source. Must be decoupled to power
ground with a minimum of 4.7μF ceramic or other low
ESR capacitor. Do not use the INTV
purpose.
EXTV
Connected to INTV
bypassing the internal LDO powered from V
EXTV
the Applications Information section. Do not exceed 14V
on this pin.
PGND (Pin 21): Driver Power Ground. Connects to the
sources of bottom (synchronous) N-channel MOSFETs
and the (–) terminal(s) of C
V
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
BOOST1, BOOST2 (Pin 24, Pin 17): Bootstrapped Supplies
to the Topside Floating Drivers. Capacitors are connected
between the BOOST and SW pins and Schottky diodes are
tied between the BOOST and INTV
at the BOOST pins is from INTV
SW1, SW2 (Pin 25, Pin 16): Switch Node Connections
to Inductors.
IN
(Pin 22): Main Supply Pin. A bypass capacitor should
CC
CC
CC
(Pin 19): Output of the Internal Linear Low Dropout
IN
(Pin 20): External Power Input to an Internal LDO
is higher than 4.7V. See EXTV
capacitors.
CC
. This LDO supplies INTV
IN
.
CC
CC
to (V
CC
pins. Voltage swing
pin for any other
CC
IN
+ INTV
Connection in
CC
IN
.
CC
whenever
CC
power,
).
3890f