LTC3858 Linear Technology, LTC3858 Datasheet - Page 9

• Manufacturer Part Number: LTC3858
• Description: Synchronous Step-Down Controller
• Manufacturer: Linear Technology

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
Inputs. Tying this pin to SGND, FLOAT or INTV
maximum current sense threshold to one of three different
levels for both comparators.
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
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
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
pin FuncTions
LIM
IN
(Pin 22): Main Input Supply Pin. A bypass capacitor
(Pin 28): Current Comparator Sense Voltage Range
CC
CC
CC
(Pin 19): Output of the Internal Linear Low Dropout
is higher than 4.7V. See EXTV
(Pin 20): External Power Input to an Internal LDO
CC
. This LDO supplies INTV
IN
.
CC
to (V
CC
CC
pins. Voltage swing
pin for any other
CC
IN
+ INTV
Connection in
CC
IN
.
CC
whenever
CC
sets the
CC
power,
).
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
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
SS1, SS2 (Pin 29, Pin 13): External Soft-Start Input. The
LTC3858 regulates the V
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
Switching Regulator Compensation Points. Each associ-
ated channel’s current comparator trip point increases
with this control voltage.
V
feedback voltage for each controller from an external
resistive divider across the output.
SENSE1
the differential current comparators that are normally
connected to inductor DCR sensing networks or current
sensing resistors. The I
between the SENSE
R
TH1
FB1
SENSE
, I
, V
TH2
set the current trip threshold.
FB2
+
FB1,2
, SENSE2
(Pin 30, Pin 12): Error Amplifier Outputs and
(Pin 31, Pin 11): Receives the remotely sensed
pin is not within ±10% of its set point.
+
–
and SENSE
(Pin 32, Pin 10): The (+) Input to
TH
FB1,2
pin voltage and controlled offsets
voltage to the smaller of 0.8V
+
pins in conjunction with
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LTC3858
CC
– 0.5V
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