LTC3858_15 Datasheet, PDF (9/38 Pages) Linear Technology – Low IQ, Dual 2-Phase Synchronous Step-Down Controller

LTC3858
PIN FUNCTIONS
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 LTC3858, reducing quiescent
current to approximately 8μA. Do NOT float these pins.
I_LIM (Pin 28): Current Comparator Sense Voltage Range
Inputs. Tying this pin to SGND, FLOAT or INTV_CC sets the
maximum current sense threshold to one of three different
levels for both comparators.
INTV_CC (Pin 19): Output of the Internal Linear Low Dropout
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_CC pin for any other
purpose.
EXTV_CC (Pin 20): External Power Input to an Internal LDO
Connected to INTV_CC. This LDO supplies INTV_CC power,
bypassing the internal LDO powered from V_IN whenever
EXTV_CC is higher than 4.7V. See EXTV_CC Connection in
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_IN.
V_IN (Pin 22): Main Input Supply Pin. A bypass capacitor
should 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 (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_CC pins. Voltage swing
at the BOOST pins is from INTV_CC to (V_IN + INTV_CC).
SW1, SW2 (Pin 25, Pin 16): Switch Node Connections
to Inductors.
TG1, TG2 (Pin 26, Pin 15): High Current Gate Drives for
Top N-Channel MOSFETs. These are the outputs of float-
ing drivers with a voltage swing equal to INTV_CC – 0.5V
superimposed on the switch node voltage SW.
PGOOD1, PGOOD2 (Pin 27, Pin 14): Open-Drain Logic
Output. PGOOD1,2 is pulled to ground when the voltage
on the V_FB1,2 pin is not within ±10% of its set point.
SS1, SS2 (Pin 29, Pin 13): External Soft-Start Input. The
LTC3858 regulates the V_FB1,2 voltage to the smaller of 0.8V
or the voltage on the SS1,2 pin. An internal 1μA pull-up
current source is connected to this pin. A capacitor to
ground at this pin sets the ramp time to final regulated
output voltage. This pin is also used as the short-circuit
latchoff timer.
I_TH1, I_TH2 (Pin 30, Pin 12): Error Amplifier Outputs and
Switching Regulator Compensation Points. Each associ-
ated channel’s current comparator trip point increases
with this control voltage.
V_FB1, V_FB2 (Pin 31, Pin 11): Receives the remotely sensed
feedback voltage for each controller from an external
resistive divider across the output.
SENSE1⁺, SENSE2⁺ (Pin 32, Pin 10): The (+) Input to
the differential current comparators that are normally
connected to inductor DCR sensing networks or current
sensing resistors. The I_TH pin voltage and controlled offsets
between the SENSE^– and SENSE⁺ pins in conjunction with
R_SENSE set the current trip threshold.
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