Datasheet LTC3851A (Analog Devices) - 8

LTC3851A
pin FuncTions (GN and MSE/UD) MODE/PLLIN (Pin 1/Pin 15):
Forced Continuous Mode,
ILIM (Pin 9/Pin 7):
Current Comparator Sense Voltage Burst Mode or Pulse-Skipping Mode Selection Pin and Ex- Range Input. Tying this pin to GND, FLOAT or INTVCC ternal Synchronization Input to Phase Detector Pin. Connect selects the maximum current sense threshold from three this pin to INTVCC to force continuous conduction mode dif ferent levels. of operation. Connect to GND to enable pulse-skipping
GND (Pin 10/Pin 8, Exposed Pad Pin 17):
Ground. All mode of operation. To select Burst Mode operation, tie small-signal components and compensation components this pin to INTVCC through a resistor no less than 50k, should be Kelvin connected to this ground. The (–) terminal but no greater than 250k. A clock on the pin will cause of CV the controller to operate in forced continuous mode of CC and the (–) terminal of CIN should be closely con- nected to this pin. The exposed pad should be soldered operation and synchronize the internal oscillator. to ground for good thermal conductivity.
FREQ/PLLFLTR (Pin 2/Pin 16):
The phase-locked loop’s
BG (Pin 11/Pin 9):
Bottom Gate Driver Output. This pin lowpass filter is tied to this pin. Alternatively, a resistor drives the gate of the bottom N-channel MOSFET between can be connected between this pin and GND to vary the GND and INTV frequency of the internal oscillator. CC.
INTV RUN (Pin 3/Pin 1):
Run Control Input. A voltage above
CC (Pin 12/Pin 10):
Internal 5V Regulator Output. The control circuit is powered from this voltage. Decouple this 1.22V on this pin turns on the IC. However, forcing this pin to GND with a minimum 2.2μF low ESR tantalum or pin below 1.1V causes the IC to shut down the IC. There ceramic capacitor. is a 2μA pull-up current on this pin.
V TK/SS (Pin 4/Pin 2):
Output Voltage Tracking and Soft-Start
IN (Pin 13/Pin 11):
Main Input Supply. Decouple this pin to GND with a capacitor. Input. A capacitor to ground at this pin sets the ramp rate for the output voltage. An internal soft-start current of of
BOOST (Pin 14/Pin 12):
Boosted Floating Driver Supply. 1μA charges this capacitor. The (+) terminal of the boost-strap capacitor is connected to this pin. This pin swings from a diode voltage drop
ITH (Pin 5/Pin 3):
Current Control Threshold and Error below INTV Amplifier Compensation Point. The current comparator CC up to VIN + INTVCC. tripping threshold increases with its ITH control voltage.
TG (Pin 15/Pin 13):
Top Gate Driver Output. This is the output of a floating driver with a voltage swing equal to
FB (Pin 6/Pin 4):
Error Amplifier Feedback Input. This pin INTV receives the remotely sensed feedback voltage from an CC superimposed on the switch node voltage. external resistive divider across the output.
SW (Pin 16/Pin 14):
Switch Node Connection to the In- ductor. Voltage swing at this pin is from a Schottky diode
SENSE– (Pin 7/Pin 5):
Current Sense Comparator Inverting (external) voltage drop below ground to V Input. The (–) input to the current comparator is connected IN. to the output.
SENSE+ (Pin 8/Pin 6):
Current Sense Comparator Non- inverting Input. The (+) input to the current comparator is normally connected to the DCR sensing network or current sensing resistor. 3851afa 8 Document Outline Features Applications Description 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