LT8331 datasheet(6/30 Pages) AD

6 / 30 page

LT8331

Rev. C

For more information www.analog.com

PIN FUNCTIONS

EN/UVLO (Pin 1): Shutdown and Undervoltage Detect Pin.

The LT8331 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.

A 140mV pin hysteresis ensures part switching resumes

when the pin exceeds 1.74V. 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 (Pin 3): 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 Pin 1).

INTVCC (Pin 5): Regulated 3.2V Supply for Internal Loads.

The INTVCC pin must be bypassed with a minimum 1µF

low ESR ceramic capacitor to GND. No additional com-

ponents or loading is allowed on this pin. INTVCC draws

power from the BIAS pin if 4.4V ≤ BIAS ≤ VIN – 0.4V,

otherwise INTVCC is powered by the VIN pin.

NC (Pins 6, 8): No Internal Connection. Leave these pins

open.

BIAS (Pin 7): Second Input Supply for Powering INTVCC.

Removes the majority of INTVCC current from the VIN pin

to improve efficiency when 4.4V ≤ BIAS ≤ VIN – 0.4V. If

unused, tie the pin to GND copper.

FBX (Pin 9): Voltage Regulation Feedback Pin for Positive

or Negative Outputs. Connect this pin to a resistor divider

between the output and the exposed pad GND copper

(near Pin 9). FBX reduces the switching frequency during

start-up and fault conditions when FBX is close to 0V.

RT (Pin 10): A resistor from this pin to the exposed pad

GND copper (near Pin 9) programs switching frequency.

SS (Pin 11): Soft-Start Pin. Connect a capacitor from this

pin to GND copper (near Pin 9) to control the ramp rate of

inductor current during converter start-up. SS pin charg-

ing current is 2μA. An internal 250Ω MOSFET discharges

this pin during shutdown or fault conditions.

SYNC/MODE (Pin 12): This pin allows three selectable

modes for optimization of performance.

1. GND: For Burst Mode operation (low IQ and low output

voltage ripple at light loads).

2. External Clock : For synchronized switching frequency.

3. INTVCC: For pulse-skipping mode (at light load or low

duty cycle).

SW1, SW2 (Pins 14, 16): Outputs of the Internal Power

Switch. Minimize the metal trace area connected to these

pins to reduce EMI.

PGND,GND (Pin 17): Power Ground and Signal Ground

for the IC. The package has an exposed pad (Pin 17)

underneath the IC which is the best path for heat out of

the package. Pin 17 should be soldered to a continuous

copper ground plane under the device to reduce die tem-

perature and increase the power capability of the LT8331.

Connect power ground components to the exposed pad

copper exiting near Pins 1, 14 and 16. Connect signal

ground components to the exposed pad copper exiting

near Pins 8 and 9.

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