LTC3708 LINER [Linear Technology], LTC3708 Datasheet - Page 8

• Manufacturer Part Number: LTC3708
• Description: Fast 2-Phase, No RSENSE Buck Controller with Output Tracking
• Manufacturer: LINER [Linear Technology]

PIN FUNCTIONS
LTC3708
RUN/SS (Pin 1): Run Control and Soft-Start Input. A
capacitor to ground at this pin sets the ramp rate of the
output voltage (approximately 0.5s/μF) and the time delay
for overcurrent latchoff (see Applications Information).
Forcing this pin below 0.8V shuts down the LTC3708.
I
and Current Control Threshold. The current comparator
threshold increases with this control voltage. The voltage
ranges from 0V to 2.4V with 0.8V corresponding to zero
sense voltage (zero current).
V
This pin connects the error amplifi er input to an external
resistive divider from V
be implemented, if desired, using this pin.
TRACK1, TRACK2 (Pins 4, 6): Tie TRACK2 pin to a re-
sistive divider connected to the output of channel 1 for
either coincident or ratiometric output tracking. TRACK1
is used in the same manner between multiple LTC3708s
(see Applications Information). To disable this feature, tie
the pins to V
SGND (Pins 5, 33): Signal Ground. All small-signal com-
ponents and compensation components should connect to
this ground and eventually connect to PGND at one point.
The Exposed Pad of the LTC3708EUH must be soldered
to the PCB.
EXTLPF (Pin 9): Filter Connection for the External PLL. This
PLL is used to synchronize the LTC3708 to an external clock.
If external clock is not used, leave this pin fl oating.
INTLPF (Pin 10): Filter Connection for the Internal PLL.
This PLL is used to phase shift the second channel to the
fi rst channel by 180°.
V
SGND with an RC fi lter (10Ω, 1μF for example).
DRV
drivers for the bottom gates. Also used for charging the
bootstrap capacitors.
BG1, BG2 (Pins 22, 20): Bottom Gate Drive. Drives the
gate of the bottom N-channel MOSFET between ground
and DRV
8
TH1
FB1
CC
, I
CC
, V
(Pin 17): Main Input Supply. Decouple this pin to
TH2
(Pin 21): Driver Supply. Provides supply to the
FB2
CC
(Pins 2, 8): Error Amplifi er Compensation Point
.
(Pins 3, 7): Error Amplifi er Feedback Input.
CC
. Do Not Float These Pins.
OUT
. Additional compensation can
PGND1, PGND2 (Pins 23, 19): Power Ground. Connect this
pin closely to the source of the bottom N-channel MOSFET,
the (–) terminal of C
SENSE1–, SENSE2– (Pins 24, 18): Current Sense Com-
parator Input. The (–) input to the current comparator is
used to accurately Kelvin sense the bottom side of the
sense resistor or MOSFET.
SENSE1
parator Input. The (+) input to the current comparator is
normally connected to the SW node unless using a sense
resistor (See Applications Information).
SW1, SW2 (Pins 26, 15): Switch Node. The (–) terminal of the
bootstrap capacitor C
a Schottky diode voltage drop below ground up to V
TG1, TG2 (Pins 27, 14): Top Gate Drive. Drives the top
N-channel MOSFET with a voltage swing equal to DRV
superimposed on the switch node voltage SW.
BOOST1, BOOST2 (Pins 28, 13): Boosted Floating Driver
Supply. The (+) terminal of the bootstrap capacitor C
connects here. This pin swings from a diode voltage drop
below DRV
I
resistor from V
current and thereby set the switching frequency.
PGOOD (Pin 30): Power Good Output. Open-drain logic
output that is pulled to ground when either or both output
voltages are not within ±10% of the regulation point. The
output voltage must be out of regulation for at least 100μs
before the power good output is pulled to ground.
FCB (Pin 31): Forced Continuous and External Clock Input.
Tie this pin to ground to force continuous synchronous
operation or to V
tion at light load. Feeding an external clock signal into this
pin will synchronize the LTC3708 to the external clock and
enable forced continuous mode.
V
The voltage at this pin is ten times the nominal sense volt-
age at maximum output current and can be programmed
from 0.5V to 2V. The sense voltage defaults to 70mV when
this pin is tied to ground, 140mV when tied to V
ON1
RNG1
, I
, V
ON2
+
RNG2
, SENSE2
CC
(Pins 29, 12): On-Time Current Input. Tie a
up to V
(Pins 32, 11): Sense Voltage Range Input.
IN
CC
to this pin to set the one-shot timer
+
to enable discontinuous mode opera-
DRVCC
B
(Pins 25, 16): Current Sense Com-
IN
connects here. This pin swings from
+ DRV
and the (–) terminal of C
CC
.
CC
.
IN
IN
3708fb
.
.
CC
B