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LT8331 Datasheet(HTML) 6 Page - Analog Devices

Part No. LT8331
Description  Low IQ Boost/SEPIC/Flyback/Inverting Converter with 0.5A, 140V Switch
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Homepage  http://www.analog.com
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LT8331 Datasheet(HTML) 6 Page - Analog Devices

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LT8331
6
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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