5

LT1118/LT1118-2.5

LT1118-2.85/LT1118-5

1118fc

IN: Input Supply Pin. This pin should be decoupled with a

1

µF 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 regula-

tion 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

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

≥ 0.22µF to guarantee stability. A 0.1µF ceramic capacitor

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 defined by the following formula:

Output Capacitor

The LT1118 family of voltage regulators require an output

capacitor for stability. The regulators are stable with

output capacitors larger than 0.2

µF. Load transient re-

sponse 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 capaci-

tors between 0.2

µF and 1µF give good performance in

most applications. Larger tantalum output capacitors may

be used to reduce load transient amplitudes. Larger ca-

pacitors should be paralleled with a 0.1

µF ceramic capaci-

tor to maintain quick settling time performance and to

insure stability of the regulator control loop. Capacitors

larger than 10

µF may be safely used with the regulators,

but little transient settling performance improvement re-

sults 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 pack-

ages are unable to convectively dissipate the heat gener-

ated 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

LT1118 Adjustable

GND

IN

OUT

EN

FB

1

µF

1118 TA06

LT1118

1

µF

1 +

()

OPERATIO