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LT8390

8390fa

For more information www.linear.com/LT8390

SS: Soft-Start Timer Setting. The SS pin is used to set

soft-start timer by connecting a capacitor to ground. An

internal 12.5µA pull-up current charging the external SS

capacitor gradually ramps up FB regulation voltage. A

0.1µF capacitor is recommended on this pin. Any UVLO or

thermal shutdown immediately pulls SS pin to ground and

stops switching. Using a single resistor from SS to VREF,

the LT8390 can be set in three different fault protection

modes during output short-circuit condition: hiccup (no

resistor), latch-off (499kΩ), and keep-running (100kΩ).

See more details in the Application Information section.

FB: Voltage Loop Feedback Input. The FB pin is used for

constant-voltage regulation and output fault protection.

The internal error amplifier with its output VC regulates

VFB to 1.00V through the DC/DC converter. During output

short-circuit(VFB<0.25V)condition,thepartgetsintoone

fault mode per customer setting. During an overvoltage

(VFB > 1.1V) condition, the part turns off all TG1, BG1,

TG2, BG2, and LOADTG.

VC: Error Amplifier Output to Set Inductor Current Com-

parator Threshold. The VC pin is used to compensate the

control loop with an external RC network. During LOADEN

low state, the VCpinisdisconnectedfromallinternalloads

to store its voltage information.

RT: Switching Frequency Setting. Connect a resistor from

this pin to ground to set the internal oscillator frequency

from 150kHz to 650kHz.

SYNC/SPRD: Switching Frequency Synchronization or

Spread Spectrum. Ground this pin for switching at inter-

PIN FUNCTIONS

nal oscillator frequency. Apply a clock signal for external

frequencysynchronization.TietoINTVCCfor±15%triangle

spread spectrum around internal oscillator frequency.

LOADTG: High Side PMOS Load Switch Top Gate Drive. A

bufferedandinvertedversionoftheLOADENinputsignal,the

LOADTG pin drives an external high side PMOS load switch

with a voltage swing from the higher voltage of (VOUT-5V)

and 1.2V to VOUT. Leave this pin unconnected if not used.

VOUT: Output Supply. The VOUT pin must be tied to the

power output to determine the buck, buck-boost, or boost

operation regions. The VOUTpinalsoservesaspositiverail

for the LOADTG drive. Locally bypass this pin to ground

with a minimum 1µF ceramic capacitor.

TG2: Boost Side Top Gate Drive. Drives the gate of boost

side top N-Channel MOSFET with a voltage swing from

SW2 to BST2.

SW2: Boost Side Switch Node. The SW2 pin swings from

a Schottky diode voltage drop below ground to VOUT.

BST2: Boost Side Bootstrap Floating Driver Supply. The

BST2 pin has an integrated bootstrap Schottky diode from

theINTVCCpinandrequiresanexternalbootstrapcapacitor

to the SW2 pin. The BST2 pin swings from a diode voltage

drop below INTVCC to (VOUT + INTVCC).

BG2: Boost Side Bottom Gate Drive. Drives the gate of

boost side bottom N-channel MOSFET with a voltage

swing from ground to INTVCC.

GND (Exposed Pad): Ground. Solder the exposed pad

directly to the ground plane.

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