Datasheet LT3506, LT3506A (Analog Devices) - 5

LT3506/LT3506A
TYPICAL PERFORMANCE CHARACTERISTICS RUN/SS Thresholds Frequency vs Temperature IRUN/SS vs Temperature vs Temperature
700 1.20 3.0 1.4 1.2 2.5 650 1.15 FREQUENCY (MHz) 1.0 LT3506A 2.0 TO SWITCH 0.8 600 1.10 1.5 0.6 LT3506 TO RUN FREQUENCY (kHz) 1.0 0.4 550 1.05 RUN/SS CURRENT (μA) RUNN/SS THRESHOLDS (V) 0.5 0.2 500 1.00 0 0 –50 –25 0 25 50 75 100 125 –50 –25 0 25 50 75 100 125 –50 –25 0 25 50 75 100 125 TEMPERATURE (°C) TEMPERATURE (°C) TEMPERATURE (°C) 3506 G10 3506 G13 3506 G12
PIN FUNCTIONS BOOST1 (Pin 1), BOOST2 (Pin 8):
The BOOST pins are
PG1 (Pin 14), PG2 (Pin 11):
The Power Good pins are used to provide drive voltages, higher than the input the open collector outputs of an internal comparator. PG voltage, to the internal bipolar NPN power switches. Tie remains low until the FB pin is within 10% of the fi nal through a diode from VOUT or from VIN. regulation voltage. As well as indicating output regulation, the PG pins can be used to sequence the two switching
SW1 (Pin 2), SW2 (Pin 7):
The SW pins are the outputs regulators. These pins can be left unconnected. The PG of the internal power switches. Connect these pins to the outputs are valid when V inductors, catch diodes and boost capacitors. IN is greater than 3.4V and either of the RUN/SS pins is high. The PG comparators are
VIN1 (Pins 3, 4):
The VIN1 pins supply current to the LT3506’s disabled in shutdown. internal regulator and to the internal power switch con-
V
nected to SW1. These pins must be locally bypassed.
C1 (Pin 15), VC2 (Pin 10):
The VC pins are the outputs of the internal error amps. The voltages on these pins control
VIN2 (Pins 5, 6):
The VIN2 pins supply current to the inter- the peak switch currents. These pins are normally used nal power switch connected to SW2 and must be locally to compensate the control loops, but can also be used to bypassed. Connect these pins directly to VIN1 unless power override the loops. Pull these pins to ground with an open for channel 2 is coming from a different source. drain to shut down each switching regulator.
RUN/SS1 (Pin 13), RUN/SS2 (Pin 12):
The RUN/SS pins
FB1 (Pin 16), FB2 (Pin 9):
The LT3506 regulates each are used to shut down the individual switching regula- feedback pin to 800mV. Connect the feedback resistor tors and the internal bias circuits. They also provide a divider taps to these pins. soft-start function. To shut down either regulator, pull the
Exposed Pad (Pin 17):
The Exposed Pad of the package RUN/SS pin to ground with an open drain or collector. provides both electrical contact to ground and good thermal Tie a capacitor from these pins to ground to limit switch contact to the printed circuit board. The Exposed Pad must current during start-up. If neither feature is used, leave be soldered to the circuit board for proper operation. these pins unconnected. 3506afc 5