LT8331 datasheet(7/30 Pages) AD

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LT8365

Rev. A

For more information www.analog.com

PIN FUNCTIONS

EN/UVLO: Shutdown and Undervoltage Detect Pin. The

LT8365 is shut down when this pin is low and active

when this pin is high. Below an accurate 1.6V threshold,

the part enters undervoltage lockout and stops switching.

This allows an undervoltage lockout (UVLO) threshold to

be programmed for system input voltage by resistively

dividing down system input voltage to the EN/UVLO pin.

An 80mV pin hysteresis ensures part switching resumes

when the pin exceeds 1.68V. EN/UVLO pin voltage below

0.2V reduces VIN current below 1µA. If shutdown and

UVLO features are not required, the pin can be tied directly

to system input.

VIN: Input Supply. This pin must be locally bypassed. Be

sure to place the positive terminal of the input capacitor as

close as possible to the VIN pin, and the negative terminal

as close as possible to the exposed pad PGND copper

(near EN/UVLO).

INTVCC: Regulated 3.8V Supply for Internal Loads. The

INTVCC pin must be bypassed with a 1µF low ESR ceramic

capacitor to GND. No additional components or loading is

allowed on this pin. INTVCC draws power from the BIAS

pin if 4.4V ≤ BIAS ≤ VIN, otherwise INTVCC is powered by

the VIN pin.

NC: No Internal Connection. Leave this pin open.

BIAS:SecondInputSupplyforPoweringINTVCC.Removes

the majority of INTVCC current from the VIN pin to improve

efficiency when 4.4V ≤ BIAS ≤ VIN. If unused, tie the pin

to GND.

VC: Error Amplifier Output Pin. Tie external compensation

network to this pin.

FBX:VoltageRegulationFeedbackPinforPositiveorNega-

tive Outputs. Connect this pin to a resistor divider between

the output and the exposed pad GND copper (near FBX).

FBX reduces the switching frequency during start-up and

fault conditions when FBX is close to 0V.

RT: A resistor from this pin to the exposed pad GND cop-

per (near FBX) programs switching frequency.

SS: Soft-Start Pin. Connect a capacitor from this pin to

GNDcopper(nearFBX)tocontroltheramprateofinductor

current during converter start-up. SS pin charging current

is 2μA. An internal 220Ω MOSFET discharges this pin

during shutdown or fault conditions.

SYNC/MODE: This pin allows five selectable modes for

optimization of performance.

SYNC/MODE PIN INPUT

CAPABLE MODE(S) OF OPERATION

(1) GND or <0.14V

Burst

(2) External Clock

Pulse-Skipping/Sync

(3) 100k Resistor to GND

Burst/SSFM

(4) Float (Pin Open)

Pulse-Skipping

(5) INTVCC or >1.7V

Pulse-Skipping/SSFM

where the selectable modes of operation are:

Burst = low IQ, low output ripple operation at light loads

Pulse-skipping=skippedpulse(s)atlightload(alignedtoclock)

Sync = switching frequency synchronized to external clock

SSFM=SpreadSpectrumFrequencyModulationforlowEMI.

SW1, SW2 (SW): Output of the Internal Power Switch.

Minimize the metal trace area connected to these pins to

reduce EMI.

PGND,GND: Power Ground and Signal Ground for the

IC. The package has an exposed pad underneath the IC

which is the best path for heat out of the package. The pin

should be soldered to a continuous copper ground plane

under the device to reduce die temperature and increase

thepowercapabilityoftheLT8365.Connectpowerground

componentstotheexposedpadcopperexitingneartheEN/

UVLOandSWpins.Connectsignalgroundcomponentsto

the exposed pad copper exiting near the VC and FBX pins.

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