Datasheet LT8609S (Analog Devices) - 9

LT8609S
PIN FUNCTIONS RT (Pin 1):
A resistor is tied between RT and ground to down. Tie to VIN if the shutdown feature is not used. An set the switching frequency. external resistor divider from VIN can be used to program
INTV
a VIN threshold below which the LT8609S will shut down.
CC (Pin 2):
Internal 3.5V Regulator Bypass Pin. The internal power drivers and control circuits are powered
PG (Pin 12):
The PG pin is the open-drain output of an from this voltage. INTVCC max output current is 20mA. internal comparator. PG remains low until the FB pin is Voltage on INTVCC will vary between 2.8V and 3.5V. within ±8.5% of the final regulation voltage, and there are Decouple this pin to power ground with at least a 1μF no fault conditions. PG is valid when VIN is above 3.2V and low ESR ceramic capacitor. Do not load the INTVCC pin EN/UV is high. PG will pull low when VIN is above 3.2V and with external circuitry. EN/UV is low. PG will be high impedance when VIN is low.
GND (Pins 3, 4, 8, 14, 17):
Exposed Pad Pin. These pads
FB (Pin 13):
The LT8609S regulates the FB pin to 0.774V. must be connected to the negative terminal of the input Connect the feedback resistor divider tap to this pin. capacitor and soldered to the PCB in order to lower the
TR/SS (Pin 15):
Output Tracking and Soft-Start Pin. thermal resistance. This pin allows user control of output voltage ramp rate
SW (Pins 5, 6):
The SW pin is the output of the inter- during start-up. A TR/SS voltage below 0.774V forces the nal power switches. Connect this pin to the inductor and LT8609S to regulate the FB pin to equal the TR/SS pin boost capacitor. This node should be kept small on the voltage. When TR/SS is above 0.774V, the tracking func- PCB for good performance. tion is disabled and the internal reference resumes control
N/C (Corner Pins, Pin 7):
Connect these pins to the of the error amplifier. An internal 2μA pull-up current from ground plane for improved mechanical performance while INTVCC on this pin allows a capacitor to program out- temperature cycling. put voltage slew rate. This pin is pulled to ground with a 300Ω MOSFET during shutdown and fault conditions; use
VIN (Pins 9, 10):
The VIN pin supplies current to the a series resistor if driving from a low impedance output. LT8609S internal circuitry and to the internal topside power switch. This pin must be locally bypassed. Be
SYNC (Pin 16):
External Clock Synchronization Input. sure to place the positive terminal of the input capacitor Ground this pin for low ripple Burst Mode operation at as close as possible to the V low output loads. Tie to a clock source for synchronization IN pins, and the negative capacitor terminal as close as possible to the GND pins. to an external frequency. Leave floating for pulse-skipping mode with no spread spectrum modulation. Tie to INTVCC
EN/UV (Pin 11):
The LT8609S is shut down when this or tie to a voltage between 3.2V and 5.0V for pulse-skip- pin is low and active when this pin is high. The hyster- ping mode with spread spectrum modulation. When in etic threshold voltage is 1.05V going up and 1.00V going pulse-skipping mode, the IQ will increase to several mA. Rev. D For more information www.analog.com 9 Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Typical Applications Package Description Revision History Typical Application Related Parts