LTC3862 Datasheet, PDF (9/40 Pages) Linear Technology – Multi-Phase Current Mode Step-Up DC/DC Controller

LTC3862
PIN FUNCTIONS
3V8: Output of the Internal 3.8V LDO from INTV_CC. Supply
pin for the low voltage analog and digital circuits. A low
ESR 1nF ceramic bypass capacitor should be connected
between 3V8 and SGND, as close as possible to the IC.
BLANK: Blanking Time. Floating this pin provides a nominal
minimum on-time of 260ns. Connecting this pin to 3V8
provides a minimum on-time of 340ns, while connecting
it to SGND provides a minimum on-time of 180ns.
CLKOUT: Digital Output Used for Daisy-Chaining Multiple
LTC3862 ICs in Multi-Phase Systems. The PHASEMODE
pin voltage controls the relationship between CH1 and
CH2 as well as between CH1 and CLKOUT.
D_MAX: Maximum Duty Cycle.This pin programs the maxi-
mum duty cycle. Floating this pin provides 84% duty cycle.
Connecting this pin to 3V8 provides 75% duty cycle, while
connecting it to SGND provides 96% duty cycle.
FB: Error Amplifier Input. The FB pin should be connected
through a resistive divider network to V_OUT to set the
output voltage.
FREQ: A resistor from FREQ to SGND sets the operating
frequency.
GATE1, GATE2: Gate Drive Output. The LTC3862 provides
a 5V gate drive referenced to PGND to drive a logic-level
threshold MOSFET.
INTV_CC: Output of the Internal 5V Low Dropout Regulator
(LDO). A low ESR 4.7μF (X5R or better) ceramic bypass
capacitor should be connected between INTV_CC and PGND,
as close as possible to the IC.
ITH: Error Amplifier Output. The current comparator trip
threshold increases with the ITH control voltage. The ITH
pin is also used for compensating the control loop of the
converter.
PGND: Power Ground. Connect this pin close to the
sources of the power MOSFETs. PGND should also be
connected to the negative terminals of V_IN and INTV_CC
bypass capacitors. PGND is electrically isolated from the
SGND pin. The Exposed Pad of the FE and QFN packages
is connected to PGND.
PHASEMODE: The PHASEMODE pin voltage programs
the phase relationship between CH1 and CH2 rising gate
signals, as well as the phase relationship between CH1
gate signal and CLKOUT. Floating this pin or connecting
it to either 3V8, or SGND changes the phase relationship
between CH1, CH2 and CLKOUT.
PLLFLTR: PLL Lowpass Filter Input. When synchroniz-
ing to an external clock, this pin serves as the lowpass
filter input for the PLL. A series resistor and capacitor
connected from PLLFLTR to SGND compensate the PLL
feedback loop.
RUN: Run Control Input. A voltage above 1.22V on the pin
turns on the IC. Forcing the pin below 1.22V causes the
IC to shut down. There is a 0.5μA pull-up current for this
pin. Once the RUN pin raises above 1.22V, an additional
4.5μA pull-up current is added to the pin for program-
mable hysteresis.
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