LT8705
11
8705ff
For more information www.linear.com/LT8705
pin FuncTions
SHDN (Pin 1/Pin 4): Shutdown Pin. Tie high to enable
device. Ground to shut down and reduce quiescent current
to a minimum. Do not float this pin.
CSN (Pin 2/Pin 5): The (–) Input to the Inductor Current
Sense and Reverse-Current Detect Amplifier.
CSP (Pin 3/Pin 6): The (+) Input to the Inductor Current
Sense and Reverse-Current Detect Amplifier. The V
C
pin
voltage and built-in offsets between CSP and CSN pins, in
conjunction with the R
SENSE
resistor value, set the current
trip threshold.
LDO33 (Pin 4/Pin 7): 3.3V Regulator Output. Bypass this
pin to ground with a minimum 0.1μF ceramic capacitor.
FBIN (Pin 5/Pin 8): Input Feedback Pin. This pin is con
-
nected to the input error amplifier input.
FBOUT
(
Pin 6/Pin 9): Output Feedback Pin. This pin
connects the error amplifier input to an external resistor
divider from the output.
IMON_OUT (Pin 7/Pin 10): Output Current Monitor Pin. The
current out of this pin is proportional to the output current.
See the Operation and Applications Information sections.
V
C
(Pin 8/Pin 11): Error Amplifier Output Pin. Tie external
compensation network to this pin.
SS (Pin 9/Pin 12): Soft-Start Pin. Place at least 100nF of
capacitance here. Upon start
-up, this pin will be charged
by an internal resistor to 2.5V.
CLKOUT (Pin 10/Pin 13): Clock Output Pin. Use this
pin to synchronize one or more compatible switching
regulator ICs to the LT8705. 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.
SYNC (Pin 11/Pin 14): To synchronize the switching fre
-
quency 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.
(QFN/TSSOP)
RT (Pin 12/Pin 15): Timing Resistor Pin. Adjusts the switch-
ing frequency.
Place a resistor from this pin to ground to
set the free-running frequency. Do not float this pin.
BG1, BG2 (Pins 14, 16/Pins 17, 19): Bottom Gate Drive.
Drives the gates of the bottom N-channel
MOSFETs between
ground and GATEV
CC
.
GATEV
CC
(Pin 15/Pin 18): Power Supply for Gate Drivers.
Must be connected to the INTV
CC
pin. Do not power from
any other supply. Locally bypass to GND.
BOOST1, BOOST2 (Pins 23, 17/Pins 28, 20): Boosted
Floating Driver Supply. The (+) terminal of the bootstrap
capacitor 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 (Pins 22, 18/Pins 26, 21): Top Gate Drive. Drives
the top N-channel MOSFETs with voltage swings equal
to GATEV
CC
superimposed on the switch node voltages.
SW1, SW2 (Pins 21, 19/Pins 24, 22): Switch Nodes. The
(–) terminals of the bootstrap capacitors connect here.
SRVO_FBIN (Pin 25 QFN Only): Open-Drain Logic Out
-
put. This pin is pulled to ground when the input voltage
feedback loop is active.
SRVO_IIN
(Pin 26 QFN Only): Open-Drain Logic Output.
The pin is pulled to ground when the input current loop
is active.
SRVO_IOUT (Pin 27 QFN Only): Open-Drain Logic Out
-
put. The pin is pulled to ground when the output current
feedback loop is active.
SRVO_FBOUT (Pin 28 QFN Only): Open-Drain
Logic Out-
put. This pin is pulled to ground when the output voltage
feedback loop is active.
EXTV
CC
(Pin 29/Pin 30): External V
CC
Input. When EXTV
CC
exceeds 6.4V (typical), INTV
CC
will be powered from this
pin. When EXTV
CC
is lower than 6.22V (typical), INTV
CC
will be powered from V
IN
.
CSNOUT (Pin 30/Pin 32): The (–) Input to the Output Cur-
rent Monitor
Amplifier. Connect this pin to V
OUT
when not
in use. See Applications Information section for proper
use of this pin.
