LT8604 datasheet(8/20 Pages) AD

8 / 20 page

LT8604

Rev. 0

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BST (Pin 1): This pin is used to provide a drive volt-

age higher than the input voltage, to the topside power

switch. Place a 47nF boost capacitor as close as possible

to the IC. Do not put resistance in series with this pin.

SW (Pin 2): The SW pin is the output of the internal power

switches. Connect this pin to the inductor. This node

should be kept small on the PCB for good performance.

BIAS (Pin 3): The internal regulator will draw current from

BIAS instead of VIN when BIAS is tied to a voltage higher

than 3.2V. For output voltages of 3.3V to 25V this pin

should be tied to VOUT. If this pin is tied to a supply other

than VOUT, use a 1µF local bypass capacitor on this pin.

If no supply is available, tie this pin to GND.

INTVCC (Pin 4): Internal 3.4V Regulator Bypass Pin. The

internal power drivers and control circuits are powered

from this voltage. INTVCC maximum output current is

2mA. Do not load the INTVCC pin with external circuitry.

INTVCC current will be supplied from BIAS if BIAS >

3.2V, otherwise current will be drawn from VIN. Voltage

on INTVCC will vary between 2.8V and 3.4V when VBIAS

is between 3.0V and 3.6V. Decouple this pin to power

ground with a low ESR ceramic capacitor of at least 1μF

placed close to the IC.

RT (Pin 5): Tie a resistor between RT and ground to set

the switching frequency.

FB (Pin 6): The LT8604 regulates the FB pin to 0.778V.

Connect the feedback resistor divider tap to this pin.

TR/SS (Pin 7): Output Tracking and Soft-Start Pin. This

pin allows user control of output voltage ramp rate dur-

ing start-up. A TR/SS voltage below 0.778V forces the

LT8604 to regulate the FB pin to equal the TR/SS pin volt-

age. When TR/SS is above 0.778V, the tracking function is

disabled and the internal reference resumes control of the

error amplifier. An internal 2µA pull-up current on this pin

allows a capacitor to program output voltage slew rate.

This pin is pulled to ground with a 300Ω MOSFET during

shutdown and fault conditions; use a series resistor if

driving from a low impedance output.

PG (Pin 8): The PG pin is the open-drain output of an

internal comparator. PG remains low until the FB pin is

within ±7.5% of the final regulation voltage, and there are

no fault conditions. PG is valid when VIN is above 3.2V,

regardless of EN/UV pin state.

EN/UV (Pin 9): The LT8604 is shut down when this pin is

low and active when high. The hysteretic threshold volt-

age is 1.05V rising and 1.00V falling. Tie to VIN if the

shutdown feature is not used. An external resistor divider

from VIN can be used to program a VIN threshold below

which the LT8604 will shut down.

VIN (Pin 10): The VIN pin supplies current to the LT8604

internal circuitry and to the internal top side power switch.

This pin must be locally bypassed. Be sure to place the

positive terminal of the input capacitor as close as pos-

sible to the VIN pin, and the negative capacitor terminal

as close as possible to the GND pin.

GND (Exposed Pad Pin 11): Ground. The exposed pad

must be connected to the negative terminal of the input

capacitor and soldered to the PCB in order to lower the

thermal resistance.

PIN FUNCTIONS

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