Datasheet LT8609, LT8609A, LT8609B (Analog Devices) - 10

LT8609/LT8609A/LT8609B
PIN FUNCTIONS BST:
This pin is used to provide a drive voltage, higher
TR/SS:
Output Tracking and Soft-Start Pin. This pin allows than the input voltage, to the topside power switch. Place user control of output voltage ramp rate during start-up. A a 0.1µF boost capacitor as close as possible to the IC. Do TR/SS voltage below 0.782V forces the LT8609/LT8609A/ not place a resistor in series with this pin. LT8609B to regulate the FB pin to equal the TR/SS pin
SW:
The SW pin is the output of the internal power voltage. When TR/SS is above 0.782V, the tracking function switches. Connect this pin to the inductor and boost is disabled and the internal reference resumes control of capacitor. This node should be kept small on the PCB for the error amplifier. An internal 2μA pull-up current from good performance. INTVCC on this pin allows a capacitor to program output voltage slew rate. This pin is pulled to ground with a 300Ω
INTVCC:
Internal 3.5V Regulator Bypass Pin. The internal MOSFET during shutdown and fault conditions; use a series power drivers and control circuits are powered from this resistor if driving from a low impedance output. voltage. INTVCC max output current is 20mA. Voltage on INTV
PG:
The PG pin is the open-drain output of an internal CC will vary between 2.8V and 3.5V. Decouple this pin to power ground with at least a 1μF low ESR ceramic comparator. PG remains low until the FB pin is within capacitor. Do not load the INTV ±8.5% of the final regulation voltage, and there are no fault CC pin with external circuitry. conditions. PG is valid when VIN is above 3.2V, regardless
RT:
A resistor is tied between RT and ground to set the of EN/UV pin state. switching frequency.
VIN:
The VIN pin supplies current to the LT8609/LT8609A/
SYNC:
External Clock Synchronization Input. Ground this LT8609B internal circuitry and to the internal topside power pin for low ripple Burst Mode operation at low output loads. switch. This pin must be locally bypassed. Be sure to Tie to a clock source for synchronization to an external place the positive terminal of the input capacitor as close frequency. Leave floating for pulse-skipping mode with as possible to the VIN pins, and the negative capacitor no spread spectrum modulation. Tie to INTVCC or tie to terminal as close as possible to the GND pins. a voltage between 3.2V and 5.0V for pulse-skipping mode with spread spectrum modulation. When in pulse-skipping
EN/UV:
The LT8609/LT8609A/LT8609B is shut down mode, the I when this pin is low and active when this pin is high. The Q will increase to several mA. In the LT8609B, the SYNC pin is replaced with a no connect; the LT8609B hysteretic threshold voltage is 1.05V going up and 1.00V operates in pulse-skipping mode without spread spectrum. going down. Tie to VIN if the shutdown feature is not used. An external resistor divider from VIN can be used to pro-
FB:
The LT8609/LT8609A/LT8609B regulates the FB pin gram a VIN threshold below which the LT8609/LT8609A/ to 0.782V. Connect the feedback resistor divider tap to LT8609B will shut down. this pin.
GND:
Exposed Pad Pin. The exposed pad must be con- nected to the negative terminal of the input capacitor and soldered to the PCB in order to lower the thermal resistance. 8609fg 10 For more information www.linear.com/LT8609 Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Typical Applications Package Description Revision History Typical Application Related Parts