Datasheet LT8618, LT8618-3.3 (Analog Devices) - 8

LT8618/LT8618-3.3
PIN FUNCTIONS BST (Pin 1):
This pin is used to provide a drive volt-
TR/SS (Pin 7):
Output Tracking and Soft-Start Pin. This age higher than the input voltage, to the topside power pin allows user control of output voltage ramp rate dur- switch. Place a 47nF boost capacitor as close as possible ing start-up. A TR/SS voltage below 0.778V forces the to the IC. Do not put resistance in series with this pin. LT8618 to regulate the FB pin to equal the TR/SS pin volt-
SW (Pin 2):
The SW pin is the output of the internal power age. When TR/SS is above 0.778V, the tracking function is switches. Connect this pin to the inductor. This node disabled and the internal reference resumes control of the should be kept small on the PCB for good performance. error amplifier. An internal 2µA pull-up current on this pin allows a capacitor to program output voltage slew rate.
BIAS (Pin 3):
The internal regulator will draw current from This pin is pulled to ground with a 300Ω MOSFET during BIAS instead of VIN when BIAS is tied to a voltage higher shutdown and fault conditions; use a series resistor if than 3.2V. For output voltages of 3.3V to 25V this pin driving from a low impedance output. should be tied to VOUT. If this pin is tied to a supply other than V
PG (Pin 8):
The PG pin is the open-drain output of an OUT, use a 1µF local bypass capacitor on this pin. If no supply is available, tie this pin to GND. internal comparator. PG remains low until the FB pin is within ±7.5% of the final regulation voltage, and there are
INTVCC (Pin 4):
Internal 3.4V Regulator Bypass Pin. The no fault conditions. PG is valid when VIN is above 3.4V, internal power drivers and control circuits are powered regardless of EN/UV pin state. from this voltage. INTVCC maximum output current is 2mA. Do not load the INTV
EN/UV (Pin 9):
The LT8618 is shut down when this pin is CC pin with external circuitry. INTV low and active when high. The hysteretic threshold volt- CC current will be supplied from BIAS if BIAS > 3.2V, otherwise current will be drawn from V age is 1.05V rising and 1.00V falling. Tie to VIN if the IN. Voltage on INTV shutdown feature is not used. An external resistor divider CC will vary between 2.8V and 3.4V when VBIAS is between 3.0V and 3.6V. Decouple this pin to power from VIN can be used to program a VIN threshold below ground with a low ESR ceramic capacitor of at least 1μF which the LT8618 will shut down. placed close to the IC.
VIN (Pin 10):
The VIN pin supplies current to the LT8618
RT (Pin 5):
Tie a resistor between RT and ground to set internal circuitry and to the internal top side power switch. the switching frequency. This pin must be locally bypassed. Be sure to place the positive terminal of the input capacitor as close as pos-
FB (Pin 6, LT8618 Only):
The LT8618 regulates the FB sible to the VIN pin, and the negative capacitor terminal pin to 0.778V. Connect the feedback resistor divider tap as close as possible to the GND pin. to this pin.
GND (Exposed Pad Pin 11):
Ground. The exposed pad
OUT (Pin 6, LT8618-3.3 Only):
The LT8618-3.3 regulates must be connected to the negative terminal of the input the OUT pin to 3.3V. This pin connects to the internal capacitor and soldered to the PCB in order to lower the feedback divider that programs the fixed output voltage. thermal resistance. Tie the output to this pin. Rev. 0 8 For more information www.analog.com Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Pin Configuration Pin Functions Block Diagram Operation Applications Information Typical Applications Package Description Typical Application Related Parts