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 0.1µF boost capacitor as close as possible to the IC. Do A TR/SS voltage below 0.782V forces the LT8609/ not place a resistor in series with this pin. LT8609A/LT8609B to regulate the FB pin to equal the
SW:
The SW pin is the output of the internal power TR/SS pin voltage. When TR/SS is above 0.782V, the switches. Connect this pin to the inductor and boost tracking function is disabled and the internal reference capacitor. This node should be kept small on the PCB for resumes control of the error amplifier. An internal 2μA good performance. pull-up current from INTVCC on this pin allows a capacitor to program output voltage slew rate. This pin is pulled
INTVCC:
Internal 3.5V Regulator Bypass Pin. The inter- to ground with a 300Ω MOSFET during shutdown and nal power drivers and control circuits are powered from fault conditions; use a series resistor if driving from a low this voltage. INTVCC max output current is 20mA. Voltage impedance output. on INTVCC will vary between 2.8V and 3.5V. Decouple this pin to power ground with at least a 1μF low ESR
PG:
The PG pin is the open-drain output of an internal ceramic capacitor. Do not load the INTV comparator. PG remains low until the FB pin is within CC pin with exter- nal circuitry. ±8.5% of the final regulation voltage, and there are no fault conditions. PG is valid when VIN is above 3.2V,
RT:
A resistor is tied between RT and ground to set the regardless of EN/UV pin state. switching frequency.
VIN:
The VIN pin supplies current to the LT8609/LT8609A/
SYNC:
External Clock Synchronization Input. Ground LT8609B internal circuitry and to the internal topside this pin for low ripple Burst Mode operation at low out- power switch. This pin must be locally bypassed. Be sure put loads. Tie to a clock source for synchronization to to place the positive terminal of the input capacitor as an external frequency. Leave floating for pulse-skipping close as possible to the VIN pins, and the negative capaci- mode with no spread spectrum modulation. Tie to INTVCC tor terminal as close as possible to the GND pins. or tie to a voltage between 3.2V and 5.0V for pulse-skip- ping mode with spread spectrum modulation. When in
EN/UV:
The LT8609/LT8609A/LT8609B is shut down pulse-skipping 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; hysteretic threshold voltage is 1.05V going up and 1.00V the LT8609B operates in pulse-skipping mode without going down. Tie to VIN if the shutdown feature is not used. spread spectrum. An external resistor divider from VIN can be used to pro- gram a VIN threshold below which the LT8609/LT8609A/
FB:
The LT8609/LT8609A/LT8609B regulates the FB pin LT8609B will shut down. to 0.782V. Connect the feedback resistor divider tap to 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. Rev. H 10 For more information www.analog.com 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