LTC3703 Linear Technology, LTC3703 Datasheet - Page 7

• Manufacturer Part Number: LTC3703
• Description: 100V Synchronous Switching Regulator Controller
• Manufacturer: Linear Technology

PI FU CTIO S
MODE/SYNC (Pin 1): Pulse Skip Mode Enable/Sync Pin.
This multifunction pin provides Pulse Skip Mode enable/
disable control and an external clock input for synchroni-
zation of the internal oscillator. Pulling this pin below 0.8V
or to an external logic-level synchronization signal dis-
ables Pulse Skip Mode operation and forces continuous
operation. Pulling the pin above 0.8V enables Pulse Skip
Mode operation. This pin can also be connected to a
feedback resistor divider from a secondary winding on the
inductor to regulate a second output voltage.
f
pin sets the free running frequency of the internal oscilla-
tor. See applications section for resistor value selection
details.
COMP (Pin 3): Loop Compensation. This pin is connected
directly to the output of the internal error amplifier. An RC
network is used at the COMP pin to compensate the
feedback loop for optimal transient response.
FB (Pin 4): Feedback Input. Connect FB through a resistor
divider network to V
connect the loop compensation network from COMP to
FB.
I
current limit comparator threshold. If the voltage drop
across the bottom MOSFET exceeds the magnitude of the
voltage at I
I
current threshold to be set with a single external resistor
to ground. See the Current Limit Programming section for
more information on choosing R
INV (Pin 6): Top/Bottom Gate Invert. Pulling this pin above
2V sets the controller to operate in step-up (boost) mode
with the TG output driving the synchronous MOSFET and
the BG output driving the main switch. Below 1V, the
controller will operate in step-down (buck) mode.
RUN/SS (Pin 7): Run/Soft-Start. Pulling RUN/SS below
0.9V will shut down the LTC3703, turn off both of the
external MOSFET switches and reduce the quiescent sup-
ply current to 50 A. A capacitor from RUN/SS to ground
will control the turn-on time and rate of rise of the output
voltage at power-up. An internal 4 A current source pull-
up at the RUN/SS pin sets the turn-on time at approxi-
mately 750ms/ F.
SET
MAX
MAX
U
(Pin 2): Frequency Set. A resistor connected to this
pin has an internal 12 A current source, allowing the
(Pin 5): Current Limit Set. The I
U
MAX
, the controller goes into current limit. The
U
OUT
to set the output voltage. Also
(GN16)
IMAX
.
MAX
pin sets the
GND (Pin 8): Ground Pin.
BGRTN (Pin 9): Bottom Gate Return. This pin connects to
the source of the pull-down MOSFET in the BG driver and
is normally connected to ground. Connecting a negative
supply to this pin allows the synchronous MOSFET’s gate
to be pulled below ground to help prevent false turn-on
during high dV/dt transitions on the SW node. See the
Applications Information section for more details.
BG (Pin 10): Bottom Gate Drive. The BG pin drives the gate
of the bottom N-channel synchronous switch MOSFET.
This pin swings from BGRTN to DRV
DRV
vides power to the BG output driver. This pin should be
connected to a voltage high enough to fully turn on the
external MOSFETs, normally 10V to 15V for standard
threshold MOSFETs. DRV
with a 10 F, low ESR (X5R or better) ceramic capacitor.
V
the output drivers are powered from this pin. V
be connected to a low noise power supply voltage between
9V and 15V and should be bypassed to GND (pin 8) with
at least a 0.1 F capacitor in close proximity to the LTC3703.
SW (Pin 13): Switch Node Connection to Inductor and
Bootstrap Capacitor. Voltage swing at this pin is from a
Schottky diode (external) voltage drop below ground to
V
TG (Pin 14): Top Gate Drive. The TG pin drives the gate of
the top N-channel synchronous switch MOSFET. The TG
driver draws power from the BOOST pin and returns to the
SW pin, providing true floating drive to the top MOSFET.
BOOST (Pin 15): Top Gate Driver Supply. The BOOST pin
supplies power to the floating TG driver. The BOOST pin
should be bypassed to SW with a low ESR (X5R or better)
0.1 F ceramic capacitor. An additional fast recovery
Schottky diode from DRV
plete floating charge-pumped supply at BOOST.
V
nected to the high voltage input of the regulator and is used
by the internal feedforward compensation circuitry to
improve line regulation. This is not a supply pin.
CC
IN
IN
.
(Pin 16): Input Voltage Sense Pin. This pin is con-
(Pin 12) : Main Supply Pin. All internal circuits except
CC
(Pin 11): Driver Power Supply Pin. DRV
CC
CC
should be bypassed to BGRTN
to BOOST will create a com-
CC
LTC3703
.
CC
CC
should
pro-
7
3703f