Datasheet LT3509 (Analog Devices) - 6

LT3509
pin FuncTions (DFN/MSOP) DA1, DA2 (Pins 1, 7/Pins 1, 8):
The DA pins are the anode in the case of overvoltage or overtemperature conditions connections for the catch diodes. These are connected in order to discharge the soft-start capacitors. The pins internally to the exposed ground pad by current sensing can also be driven by a logic control signal of up to 5.0V. resistors. In this case, it is necessary place a 10k to 50k resistor
BOOST1, BOOST2 (Pins 2, 6/Pins 2, 7):
The BOOST pins in series along with a capacitor from the RUN/SS pin to are used to dynamically boost the power transistor base ground to ensure that there will be a soft-start for both above V initial turn on and in the case of fault conditions. Do not IN to minimize the voltage drop and power loss in the switch. These should be tied to the associated switch tie these pins to VIN. pins through the boost capacitors.
RT (Pin 10/Pin 11):
The RT pin is used to set the internal
SW1, SW2 (Pins 3, 5/Pins 3, 6):
The SW pins are the oscillator frequency. A 40.2k resistor from RT to ground internal power switch outputs. These should be connected results in a nominal frequency of 1MHz. to the associated inductors, catch diode cathodes, and the
SYNC (Pin 11/Pin12):
The SYNC pin allows the switching boost capacitors. frequency to be synchronized to a external clock. Choose
V
RT resistor to set a free-run frequency at least 12% less
IN (Pin 4/Pins 4, 5):
The VIN pins supply power to the internal power switches and control circuitry. In the MSE than the external clock frequency for correct operation. package the V The SYNC pin should not be allowed to float; if not used, IN pins must be tied together. The input capacitor should be placed as close as possible to the it should be tied low through a resistance 10kΩ or less. supply pins.
BD (Pin 12/Pin 13):
The BD pin is common anode connec-
FB1, FB2 (Pins 14, 8/Pins 16, 9):
The FB pins are used tion of the internal Schottky boost diodes. This provides to set the regulated output voltage relative to the internal the power for charging the BOOST capacitors. It should reference. These pins should be connected to a resistor be locally bypassed for best performance. divider from the regulated output such that the FB pin is
Exposed Pad (Pin 15/Pin 17):
GND. This is the reference at 0.8V when the output is at the desired voltage. and supply ground for the regulator. The exposed pad
RUN/SS1, RUN/SS2 (Pins 13, 9/Pins 15, 10):
The RUN/SS must be soldered to the PCB and electrically connected to pins enable the associated regulator channel. If both pins supply ground. Use a large ground plane and thermal vias are pulled to ground, the device will shut-down to a low to optimize thermal performance. The current in the catch power state. In the range 0.8V to 2V, the regulators are diodes also flows through the GND pad to the DA pins. enabled but the peak switch current and the DA pin maxi-
AGND (Pin 14, MSOP Package Only):
This is the connected mum current are limited to provide a soft-start function. to the ground connection of the chip and may be used as a Above 2V, the full output current is available. The inputs separate return for the low current control side components. incorporate a 1µA pull-up so that they will float high or It should not be used as the only ground connection or as charge an external capacitor to provide a current limited a connection return for load side components. soft-start. The pins are pulled down by approximately 250µA 3509fd 6 For more information www.linear.com/LT3509 Document Outline Features Description Applications Typical Application Absolute Maximum Ratings Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Related Parts