Datasheet LT8604 (Analog Devices) - 8

LT8604
PIN FUNCTIONS BST (Pin 1):
This pin is used to provide a drive volt- LT8604 to regulate the FB pin to equal the TR/SS pin volt- age higher than the input voltage, to the topside power age. When TR/SS is above 0.778V, the tracking function is switch. Place a 47nF boost capacitor as close as possible disabled and the internal reference resumes control of the to the IC. Do not put resistance in series with this pin. error amplifier. An internal 2µA pull-up current on this pin
SW (Pin 2):
The SW pin is the output of the internal power allows a capacitor to program output voltage slew rate. switches. Connect this pin to the inductor. This node This pin is pulled to ground with a 300Ω MOSFET during should be kept small on the PCB for good performance. shutdown and fault conditions; use a series resistor if driving from a low impedance output.
BIAS (Pin 3):
The internal regulator will draw current from BIAS instead of V
PG (Pin 8):
The PG pin is the open-drain output of an IN when BIAS is tied to a voltage higher than 3.2V. For output voltages of 3.3V to 25V this pin internal comparator. PG remains low until the FB pin is should be tied to V within ±7.5% of the final regulation voltage, and there are OUT. If this pin is tied to a supply other than V no fault conditions. PG is valid when VIN is above 3.2V, OUT, use a 1µF local bypass capacitor on this pin. If no supply is available, tie this pin to GND. regardless of EN/UV pin state.
INTV EN/UV (Pin 9):
The LT8604 is shut down when this pin is
CC (Pin 4):
Internal 3.4V Regulator Bypass Pin. The internal power drivers and control circuits are powered low and active when high. The hysteretic threshold volt- from this voltage. INTV age is 1.05V rising and 1.00V falling. Tie to VIN if the CC maximum output current is 2mA. Do not load the INTV shutdown feature is not used. An external resistor divider CC pin with external circuitry. INTV from VIN can be used to program a VIN threshold below CC current will be supplied from BIAS if BIAS > 3.2V, otherwise current will be drawn from V which the LT8604 will shut down. IN. Voltage on INTVCC will vary between 2.8V and 3.4V when VBIAS
VIN (Pin 10):
The VIN pin supplies current to the LT8604 is between 3.0V and 3.6V. Decouple this pin to power internal circuitry and to the internal top side power switch. ground with a low ESR ceramic capacitor of at least 1μF This pin must be locally bypassed. Be sure to place the placed close to the IC. positive terminal of the input capacitor as close as pos-
RT (Pin 5):
Tie a resistor between RT and ground to set sible to the VIN pin, and the negative capacitor terminal the switching frequency. as close as possible to the GND pin.
FB (Pin 6):
The LT8604 regulates the FB pin to 0.778V.
GND (Exposed Pad Pin 11):
Ground. The exposed pad Connect the feedback resistor divider tap to this pin. must be connected to the negative terminal of the input capacitor and soldered to the PCB in order to lower the
TR/SS (Pin 7):
Output Tracking and Soft-Start Pin. This thermal resistance. pin allows user control of output voltage ramp rate dur- ing start-up. A TR/SS voltage below 0.778V forces the Rev. 0 8 For more information www.analog.com 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 Typical Application Related Parts