LT8708-1
10
Rev 0
For more information
PIN FUNCTIONS
CLKOUT (Pin 1): Clock Output Pin. Use this pin to syn-
chronize one or more compatible switching regulator ICs.
CLKOUT toggles at the same frequency as the internal
oscillator or as the SYNC pin, but is approximately 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 a capacitor from this pin
to ground. A capacitor identical to the SS pin capacitor
used on the master LT8708 is recommended. 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. Do not 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.
It is recommended to use the same value R
SENSE
as the
master LT8708.
ICN (Pin 6): Negative V
OUT
Current Command Pin. The
voltage on this pin determines the negative V
OUT
current
for LT8708-1 to regulate to. Connect this pin to the master
LT8708’s ICN pin. See the Applications Information sec-
tion 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
. Drive this pin with the same control
signal, or connect this pin to the same voltages as the
master LT8708.
FBIN (Pin 8): V
IN
Feedback Pin. This pin is connected to
the input of error amplifier EA3. Typically, connect this pin
to LDO33 to disable the EA3.
FBOUT (Pin 9): V
OUT
Feedback Pin. This pin is connected
to the input of error amplifier EA4. Typically, connect this
pin to GND to disable the EA4.
V
C
(Pin 10): Error Amplifier Output Pin. Tie external com-
pensation 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 cur-
rent 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
Applications 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. It is recommended to use the same value
R
T
resistor as the master LT8708. 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. In a two-phase
system, connect this pin to the master LT8708’s CLKOUT
pin to have a 180° phase shift. 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. It is recom-
mended to use the same value bypass cap as the master
LT8708.
