Datasheet LT3972 (Analog Devices) - 7

LT3972
PIN FUNCTIONS BD (Pin 1):
This pin connects to the anode of the boost
SYNC (Pin 6):
This is the external clock synchronization Schottky diode. BD also supplies current to the internal input. Ground this pin for low ripple Burst Mode operation at regulator. low output loads. Tie to a clock source for synchronization. Clock edges should have rise and fall times faster than 1μs.
BOOST (Pin 2):
This pin is used to provide a drive Tie Pin to GND if not used. See Synchronization section voltage, higher than the input voltage, to the internal bipolar in Applications Information. NPN power switch.
PG (Pin 7):
The PG pin is the open-collector output of an
SW (Pin 3):
The SW pin is the output of the internal power internal comparator. PG remains low until the FB pin is switch. Connect this pin to the inductor, catch diode and within 9% of the fi nal regulation voltage. PG output is valid boost capacitor. when VIN is above 3.6V and RUN/SS is high.
VIN (Pin 4):
The VIN pin supplies current to the LT3972’s
FB (Pin 8):
The LT3972 regulates the FB pin to 0.790V. internal regulator and to the internal power switch. This Connect the feedback resistor divider tap to this pin. pin must be locally bypassed.
V RUN/SS (Pin 5):
The RUN/SS pin is used to put the
C (Pin 9):
The VC pin is the output of the internal error amplifi er. The voltage on this pin controls the peak switch LT3972 in shutdown mode. Tie to ground to shut down current. Tie an RC network from this pin to ground to the LT3972. Tie to 2.5V or more for normal operation. If compensate the control loop. the shutdown feature is not used, tie this pin to the VIN pin. RUN/SS also provides a soft-start function; see the
RT (Pin 10):
Oscillator Resistor Input. Connecting a resistor Applications Information section. to ground from this pin sets the switching frequency.
Exposed Pad (Pin 11):
Ground. The Exposed Pad must be soldered to PCB.
BLOCK DIAGRAM
VIN VIN 4 C1 – INTERNAL 0.79V REF + BD 1 RUN/SS 5 3 SLOPE COMP SWITCH BOOST LATCH 2 C3 R RT OSCILLATOR Q 10 200kHzTO2.4MHz S L1 RT SW V 3 OUT SYNC DISABLE 6 C2 D1 Burst Mode SOFT-START DETECT PG 7 ERROR AMP VC CLAMP + 0.725V + VC 9 – – CC CF GND FB RC 11 8 R2 R1 3972 BD 3972fa 7