Datasheet LT8608, LT8608B (Analog Devices) - 8

LT8608/LT8608B
PIN FUNCTIONS BST:
This pin is used to provide a drive voltage, higher
TR/SS (MSOP Only):
Output Tracking and Soft-Start Pin. than the input voltage, to the topside power switch. Place This pin allows user control of output voltage ramp rate a 0.1µF boost capacitor as close as possible to the IC. Do during start-up. A TR/SS voltage below 0.778V forces the not place a resistor in series with this pin. LT8608 to regulate the FB pin to equal the TR/SS pin volt-
SW:
The SW pin is the output of the internal power age. When TR/SS is above 0.778V, 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. There is voltage. INTVCC max output current is 20mA. Voltage on no TR/SS pin in the LT8608 DFN or LT8608B and the node INTVCC will vary between 2.8V and 3.5V. Decouple this is internally floated. pin to power ground with at least a 1μF low ESR ceramic capacitor. Do not load the INTV
PG:
The PG pin is the open-drain output of an internal CC pin with external circuitry. comparator. PG remains low until the FB pin is within
RT:
A resistor is tied between RT and ground to set the ±8.5% of the final regulation voltage, and there are no fault switching frequency. When synchronizing, the RT resistor conditions. PG is valid when VIN is above 3.2V, regardless should be chosen to set the LT8608 switching frequency of EN/UV pin state. equal to or below the lowest synchronization input.
VIN:
The VIN pin supplies current to the LT8608 internal
SYNC (MSOP Only):
External Clock Synchronization Input. circuitry and to the internal topside power switch. This pin Ground this pin for low ripple Burst Mode operation at low must be locally bypassed. Be sure to place the positive output loads. Tie to a clock source for synchronization to terminal of the input capacitor as close as possible to the an external frequency. Leave floating for pulse-skipping VIN pins, and the negative capacitor terminal as close as mode with no spread spectrum modulation. Tie to INTVCC possible to the GND pins. or tie to a voltage between 3.2V and 5.0V for pulse-skipping mode with spread spectrum modulation. When in pulse-
EN/UV:
The LT8608 is shut down when this pin is low and skipping mode, the I active when this pin is high. The hysteretic threshold volt- Q will increase to several mA. There is no SYNC pin in the LT8608 DFN package. The LT8608 age is 1.05V going up and 1.00V going down. Tie to VIN DFN package internally ties SYNC to ground. The LT8608B if the shutdown feature is not used. An external resistor DFN package internally floats SYNC. divider from VIN can be used to program a VIN threshold below which the LT8608 will shut down.
FB:
The LT8608 regulates the FB pin to 0.778V. 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 C 8 For more information www.analog.com Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Pin Functions Block Diagram Operation Applications Information Typical Applications Package Description Revision History Typical Application Related Parts