Datasheet

LT8619/LT8619-5
10
Rev A
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PIN FUNCTIONS
NC (Pin 1, 3, 13, MSOP Only): No Connect. These pins
are not connected to the internal circuitry.
V
IN
(Pin 1/Pin 2): The V
IN
pin supplies current to the
LT8619 internal circuitry and to the internal topside power
switch. Be sure to place the positive terminal of the input
bypass capacitor as close as possible to the V
IN
pin, and
the negative capacitor terminal as close as possible to
the GND pin.
EN/UV (Pin 2/Pin 4): The LT8619 is shut down when this
pin is low and active when this pin is high. The EN/UV pin
power-on threshold is 1V. When forced below 0.56V, the
IC is put into a low current shutdown mode. Tie to V
IN
if
shutdown feature is not used. An external resistor divider
from V
IN
can be used to program the V
IN
UVLO.
RT (Pin 3/Pin 5): A resistor is tied between RT and ground
to set the switching frequency. When synchronizing, the
R
T
resistor should be chosen to set the LT8619 switch-
ing frequency equal to or below the synchronization fre-
quency. Do not apply external voltage to this pin.
PG (Pin 4/Pin 6): Open-Drain Power Good Output. PG
remains low until the FB pin is within ±7.5% of the final
regulation voltage. The PG pull-up resistor can be con-
nected to the INTV
CC
, V
OUT
or an external supply voltage
that is lower than 6V.
SYNC (Pin 5/Pin 7): External Clock Synchronization Input.
Tie to a clock source for synchronization to an external
frequency. During clock synchronization, the controller
enters forced continuous mode. Ground the SYNC pin for
Burst Mode operation. Connect to INTV
CC
to enable forced
continuous mode operation. Floating this pin will enable
pulse-skipping mode operation. During start-up, the con-
troller is forced to run in pulse-skipping mode. When in
pulse-skipping or forced continuous mode operation, the
I
Q
will be much higher compared to Burst Mode operation.
FB (Pin 6/Pin 9, 10, LT8619 Only): The LT8619 regulates
the FB pin to 0.8V. Connect the feedback resistor divider
tap to this pin. Also, connect a phase lead capacitor
between FB and V
OUT
. Typically, this capacitor is between
4.7pF to 10pF. Do not apply an external voltage to this pin.
OUT (Pin 9, 10, LT8619-5 MSOP Only): Connect to the
regulator output V
OUT
. The LT8619-5 regulates the OUT
pin to 5V. This pin connects to the internal 10MΩ feed-
back divider that programs the fixed output voltage.
BIAS (Pin 7/Pin 11)
:
The internal regulator will draw cur-
rent from BIAS instead of V
IN
when the BIAS pin is tied
to a voltage higher than 3.1V. For switching regulator
output voltages of 3.3V and above, this pin should be tied
to V
OUT
. If this pin is tied to a supply other than V
OUT
, use
a 1μF local bypass capacitor on this pin.
INTV
CC
(Pin 8/Pin 12): Internal 3.3V Regulator Output.
The internal power drivers and control circuits are pow-
ered from this voltage. INTV
CC
maximum output current
is 20mA. INTV
CC
current will be supplied from BIAS if
V
BIAS
> 3.1V, otherwise current will be drawn from V
IN
.
Voltage on INTV
CC
will vary between 2.8V and 3.3V when
V
BIAS
is between 3.0V and 3.5V. Decouple this pin to GND
with at least a 1μF low ESR ceramic capacitor. Do not load
the INTV
CC
pin with external circuitry.
BST (Pin 9/Pin 14): This pin is used to provide a drive
voltage, higher than the input voltage, to the topside
power switch. Place a 0.1μF boost capacitor as close as
possible to theIC.
SW (Pin 10/Pin 15, 16): The SW pin is the output of the
internal power switches. Connect this pin to the inductor
and boost capacitor. This node should be kept small on
the PCB for good performance.
GND (Exposed Pad Pin 11/Pin 8, Exposed Pad Pin 17):
Ground. The exposed pad must be connected to the nega-
tive terminal of the input capacitor and soldered to the
PCB in order to lower the thermal resistance.
(DFN/MSOP)
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