LT1118/LT1118-2.5
LT1118-2.85/LT1118-5
5
1118fd
PIN FUNCTIONS
IN: Input Supply Pin. This pin should be decoupled with
a 1μF or larger low ESR capacitor. The two IN pins on the
SO-8 package must be directly connected on the printed
circuit board to prevent voltage drops between the two
inputs. When used as a SCSI active termination, IN con-
nects to term power. When used as a supply splitter, IN is
also the positive supply output.
GND: Ground Pin. The multiple GND pins on the SO-8
package are internally connected, but lowest load regulation
errors will result if these pins are tightly connected on the
printed circuit board. This will also aid heat dissipation at
high power levels.
EN: TTL/CMOS Logic Input. A high level allows normal
operation. A low level reduces supply current to zero. This
pin is internally connected to V
IN
on 3-lead ST packaged
devices.
OUT: Regulated Output Voltage. Output can source or sink
current. Current limit for sourcing and sinking current is
provided to protect the device from fault conditons. The
output must have a low ESR output fi lter capacitor. C
OUT
≥ 0.22μF to guarantee stability. A 0.1μF ceramic capacitor
may be needed in parallel with C
OUT
if the ESR of the main
C
OUT
is too high.
FB: Feedback Pin. The feedback pin is used to program
the output voltage of the adjustable S8 part. The output
voltage range that can be achieved is 2.1V to 6.5V. The
output voltage is determined by the selection of feedback
resistors defi ned by the following formula:
V
OUT
= V
FB
(1 + R
1
/R
2
) + I
FB
R
1
OPERATION
GND
IN OUT
EN FB
R
1
R
2
1μF
V
IN
1118 TA06
LT1118
1μF
R
1
R
2
1 +V
OUT
= V
FB
+ I
FB
R
1
()
LT1118 Adjustable
Output Capacitor
The LT1118 family of voltage regulators require an output
capacitor for stability. The regulators are stable with out-
put capacitors larger than 0.2μF. Load transient response
is very sensitive to output capacitor value and dielectric
choice. Low ESR ceramic capacitors are the best choice
for fast settling to load transients. Output capacitors
between 0.2μF and 1μF give good performance in most
applications. Larger tantalum output capacitors may be
used to reduce load transient amplitudes. Larger capaci-
tors should be paralleled with a 0.1μF ceramic capacitor
to maintain quick settling time performance and to insure
stability of the regulator control loop. Capacitors larger
than 10μF may be safely used with the regulators, but
little transient settling performance improvement results
from their use.
Worst case transient response of the LT1118 regulators
occurs at zero output current. In order to obtain the fastest
transient settling performance, the regulator output may
be preloaded with a small current. The preload current
reduces the regulator output impedance, reducing output
voltage settling time.
Thermal Considerations
The LT1118 regulators are packaged in plastic SOT-223 and
fused lead S8 packages. These small footprint packages
are unable to convectively dissipate the heat generated
when the regulator is operating at high current levels. In
order to control die operating temperatures, the PC board
layout should allow for maximum possible copper area at
the ground pins of the LT1118. The ground pins and the
tab on the SOT-223 package are electrically and thermally
