LT8708
13
Rev 0
CLKOUT (Pin 1): Clock Output Pin. Use this pin to syn-
chronize one or more compatible switching regulator ICs
to the LT8708. CLKOUT toggles at the same frequency as
the internal oscillator or as the SYNC pin, but is approxi-
mately 180° out of phase. CLKOUT may also be used as a
temperature monitor since the CLKOUT duty cycle varies
linearly with the part’s junction temperature. The CLKOUT
pin can drive capacitive loads up to 200pF.
SS (Pin 2): Soft-Start Pin. Place at least 220nF of capaci-
tance here. Upon start-up, this pin will be charged by an
internal resistor to 3.3V.
SHDN
(Pin 3): Shutdown Pin. Tie high to enable chip.
Ground to shut down and reduce quiescent current to a
minimum. Don’t float this pin.
CSN (Pin 4): The (–) Input to the Inductor Current Sense
and DCM Detect Comparator.
CSP (Pin 5): The (+) Input to the Inductor Current Sense
and DCM Detect Comparator. The V
C
pin voltage and built-
in offsets between CSP and CSN pins, in conjunction with
the R
SENSE
value, set the inductor current trip threshold.
ICN (Pin 6): Negative V
OUT
Current Monitor. The current
out of this pin is 20μA plus a current proportional to
the negative average V
OUT
current. See the Applications
Information section for more information.
DIR (Pin 7): Direction pin when MODE is set for DCM
(discontinuous conduction mode) or HCM (hybrid con-
duction mode) operation. Otherwise this pin is ignored.
Connect the pin to GND to process power from the V
OUT
to V
IN
. Connect the pin to LDO33 to process power from
the V
IN
to V
OUT
.
FBIN (Pin 8): V
IN
Feedback Pin. This pin is connected to
the input of error amplifier EA3 and is used to detect and/
or regulate low V
IN
voltage.
FBOUT (Pin 9): V
OUT
Feedback Pin. This pin is connected
to the input of error amplifier EA4 and is used to detect
and/or regulate high V
OUT
voltage.
V
C
(Pin 10): Error Amplifier Output Pin. Tie external
compensation network to this pin.
IMON_INP (Pin 11): Positive V
IN
Current Monitor and
Limit Pin. The current out of this pin is 20μA plus a current
proportional to the positive average V
IN
current. IMON_INP
also connects to error amplifier EA5 and can be used to
limit the maximum positive V
IN
current. See the Applica-
tions Information section for more information.
IMON_INN (Pin 12): Negative V
IN
Current Monitor and
Limit Pin. The current out of this pin is 20μA plus a cur-
rent proportional to the negative average V
IN
current.
IMON_INN also connects to error amplifier EA1 and can
be used to limit the maximum negative V
IN
current. See
the Applications Information section for more information.
RT (Pin 13): Timing Resistor Pin. Adjusts the switching
frequency. Place a resistor from this pin to ground to set
the frequency. Do not float this pin.
SYNC (Pin 14): To synchronize the switching frequency
to an outside clock, simply drive this pin with a clock. The
high voltage level of the clock needs to exceed 1.3V, and
the low level should be less than 0.5V. Drive this pin to less
than 0.5V to revert to the internal free-running clock. See
the Applications Information section for more information.
BG1, BG2 (Pin 16, Pin 18): Bottom Gate Drive. Drives the
gate of the bottom N-channel MOSFETs between ground
and GATEV
CC
.
GATEV
CC
(Pin 17): Power supply for bottom gate drivers.
Must be connected to the INTV
CC
pin. Do not power from
any other supply. Locally bypass to GND.
BOOST1, BOOST2 (Pin 24, Pin 19): Boosted Floating
Driver Supply. The (+) terminal of the bootstrap capaci-
tor connects here. The BOOST1 pin swings from a diode
voltage below GATEV
CC
up to V
IN
+ GATEV
CC
. The BOOST2
pin swings from a diode voltage below GATEV
CC
up to
V
OUT
+ GATEV
CC
.
TG1, TG2 (Pin 23, Pin 20): Top Gate Drive. Drives the top
N-channel MOSFETs with voltage swings equal to GATEV
CC
superimposed on the switch node voltages.
SW1, SW2 (Pin 22, Pin 21): Switch Nodes. The (–) ter-
minals of the bootstrap capacitors connect here.
PIN FUNCTIONS
