Datasheet

LT1946A
4
sn1946a 1946afs
V
C
(Pin 1): Error Amplifier Output Pin. Tie external com-
pensation network to this pin or use the internal compen-
sation network by shorting the V
C
pin to the COMP pin.
External compensation consists of placing a resistor and
capacitor in series from V
C
to GND. Typical capacitor
range is from 90pF to 270pF. Typical resistor range is from
25k to 120k.
FB (Pin 2): Feedback Pin. Reference voltage is 1.25V.
Connect resistive divider tap here. Minimize trace area at
FB. Set V
OUT
according to V
OUT
= 1.25 • (1+R1/R2).
SHDN (Pin 3): Shutdown Pin. Tie to 2.4V or more to enable
device. Ground to shut down. Do not float this pin.
GND (Pin 4, Exposed Pad): Ground. Tie both Pin 4 and
the exposed pad directly to local ground plane. The
ground metal to the exposed pad should be wide for better
heat dissipation. Multiple vias (local ground plane ↔
ground backplane) placed close to the exposed pad can
further aid in reducing thermal resistance.
SW (Pin 5): Switch Pin. This is the collector of the internal
NPN power switch. Minimize the metal trace area con-
nected to this pin to minimize EMI.
V
IN
(Pin 6): Input Supply Pin. Must be locally bypassed.
COMP (Pin 7): Internal Compensation Pin. Provides an
internal compensation network. Tie directly to the V
C
pin
for internal compensation. Tie to GND if not used.
SS (Pin 8): Soft-Start Pin. Place a soft-start capacitor
here. Upon start-up, 4µA of current charges the capacitor
to 1.5V. Use a larger capacitor for slower start-up. Leave
floating if not in use.
UU
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PI FU CTIO S