Datasheet LTC3703 (Analog Devices) - 7

LTC3703
pin FuncTions (GN16/G28) MODE/SYNC (Pin 1/Pin 6):
Pulse-Skip Mode Enable/Sync
GND (Pin 8/Pin 14):
Ground Pin. Pin. This multifunction pin provides pulse-skip mode
BGRTN (Pin 9/Pin 15):
Bottom Gate Return. This pin enable/disable control and an external clock input for connects to the source of the pull-down MOSFET in the synchronization of the internal oscillator. Pulling this pin BG driver and is normally connected to ground. Connect- below 0.8V or to an external logic-level synchronization ing a negative supply to this pin allows the synchronous signal disables pulse-skip mode operation and forces MOSFET’s gate to be pulled below ground to help prevent continuous operation. Pulling the pin above 0.8V enables false turn-on during high dV/dt transitions on the SW node. pulse-skip mode operation. This pin can also be connected See the Applications Information section for more details. to a feedback resistor divider from a secondary winding on the inductor to regulate a second output voltage.
BG (Pin 10/Pin 19):
Bottom Gate Drive. The BG pin drives the gate of the bottom N-channel synchronous switch
fSET (Pin 2/Pin 7):
Frequency Set. A resistor connected MOSFET. This pin swings from BGRTN to DRV to this pin sets the free running frequency of the internal CC. oscil ator. See Applications Information section for resistor
DRVCC (Pin 11/Pin 20):
Driver Power Supply Pin. DRVCC value selection details. provides power to the BG output driver. This pin should be connected to a voltage high enough to fully turn on
COMP (Pin 3/Pin 8):
Loop Compensation. This pin is con- the external MOSFETs, normally 10V to 15V for standard nected directly to the output of the internal error amplifier. threshold MOSFETs. DRV An RC network is used at the COMP pin to compensate CC should be bypassed to BGRTN with a 10µF, low ESR (X5R or better) ceramic capacitor. the feedback loop for optimal transient response.
V FB (Pin 4/Pin 9):
Feedback Input. Connect FB through a
CC (Pin 12/Pin 21):
Main Supply Pin. All internal circuits except the output drivers are powered from this pin. V resistor divider network to V CC OUT to set the output volt- should be connected to a low noise power supply voltage age. Also connect the loop compensation network from between 9V and 15V and should be bypassed to GND COMP to FB. (Pin 8) with at least a 0.1µF capacitor in close proximity
IMAX (Pin 5/Pin 10):
Current Limit Set. The IMAX pin sets to the LTC3703. the current limit comparator threshold. If the voltage drop
SW (Pin 13/Pin 26):
Switch Node Connection to Inductor across the bottom MOSFET exceeds the magnitude of the and Bootstrap Capacitor. Voltage swing at this pin is from a voltage at IMAX, the controller goes into current limit. The Schottky diode (external) voltage drop below ground to V I IN. MAX pin has an internal 12µA current source, allowing the current threshold to be set with a single external resistor
TG (Pin 14/Pin 27):
Top Gate Drive. The TG pin drives the to ground. See the Current Limit Programming section gate of the top N-channel synchronous switch MOSFET. for more information on choosing RIMAX. The TG driver draws power from the BOOST pin and returns to the SW pin, providing true floating drive to the
INV (Pin 6/Pin 11):
Top/Bottom Gate Invert. Pulling this top MOSFET. pin above 2V sets the controller to operate in step-up (boost) mode with the TG output driving the synchronous
BOOST (Pin 15/Pin 28):
Top Gate Driver Supply. The MOSFET and the BG output driving the main switch. Below BOOST pin supplies power to the floating TG driver. The 1V, the controller will operate in step-down (buck) mode. BOOST pin should be bypassed to SW with a low ESR (X5R or better) 0.1µF ceramic capacitor. An additional fast
RUN/SS (Pin 7/Pin 13):
Run/Soft-Start. Pulling RUN/SS recovery Schottky diode from DRV below 0.9V will shut down the LTC3703, turn off both of CC to BOOST will create a complete floating charge-pumped supply at BOOST. the external MOSFET switches and reduce the quiescent supply current to 50µA. A capacitor from RUN/SS to
VIN (Pin 16/Pin 1):
Input Voltage Sense Pin. This pin is ground will control the turn-on time and rate of rise of connected to the high voltage input of the regulator and is the output voltage at power-up. An internal 4µA current used by the internal feedforward compensation circuitry source pull-up at the RUN/SS pin sets the turn-on time to improve line regulation.
This is not a supply pin.
at approximately 750ms/µF. 3703fc 7 Document Outline Features Description Applications Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Functional Diagram Operation Applications Information Typical Applications Package Description Revision History Typical Application Related Parts