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PDF LT1118-2.5 Data sheet ( Hoja de datos )
| Número de pieza | LT1118-2.5 | |
| Descripción | Low IQ/ Low Dropout/ 800mA/ Source and Sink Regulators Adjustable and Fixed 2.5V/ 2.85V/ 5V Output | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURES
s Regulates While Sourcing or Sinking Current
s Provides Termination for up to 27 SCSI Lines
s 600µA Quiescent Current
s Ultra-Low Power Shutdown Mode
s Current Limit and Thermal Shutdown Protection
s Stable for Any CLOAD ≥ 0.22µF
s Fast Settling Time
s 1V Dropout Voltage
U
APPLICATIONS
s Active Negation SCSI Terminations
s Computers
s Disk Drives
s CD-ROM
s Supply Splitter
LT1118/LT1118-2.5
LT1118-2.85/LT1118-5
Low IQ, Low Dropout,
800mA, Source and Sink
Regulators Adjustable and
Fixed 2.5V, 2.85V, 5V Output
DESCRIPTION
The LT®1118 family of low dropout regulators has the
unique capability of maintaining output regulation while
sourcing or sinking load current. The 2.85V output voltage
regulator is ideal for use as a Boulay termination of up to
27 SCSI data lines. The regulator maintains regulation
while both sourcing and sinking current, enabling the use
of active negation drivers for improved noise immunity on
the data lines. Regulation of output voltage is maintained
for TERMPWR voltages as low as 4.0V. When unloaded,
quiescent supply current is a low 600µA, allowing continu-
ous connection to the TERMPWR lines. An ultralow power
shutdown mode is also available on the SO-8 version. In
Shutdown the output is high impedance and supply cur-
rent drops to less than 10µA.
Current limits in both sourcing and sinking modes, plus
on-chip thermal shutdown make the circuit tolerant of
output fault conditions.
The LT1118 is available in 3-lead SOT-223 and 8-lead SO
packages.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATION
IN LT1118-2.85 OUT
GND
5V 2.2µF
1µF
CERAMIC
Load Transient Response
ILOAD
1118 TA01
∆VOUT
0.2V
0V
– 0.2V
800mA
ILOAD
0mA
– 400mA
1118 TA02.tif
1
1 page  
LT1118/LT1118-2.5
LT1118-2.85/LT1118-5
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 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
pin is internally connected to VIN 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 filter capacitor. COUT
≥ 0.22µF to guarantee stability. A 0.1µF ceramic capacitor
may be needed in parallel with COUT if the ESR of the main
COUT is too high.
FB: Feedback Pin. The feedback pin is used to program the
output voltage of the adjustable S8 part. The output
voltage is determined by the selection of feedback resis-
tors defined by the following formula:
VOUT = VFB (1 + R1/R2) + IFBR1
LT1118 Adjustable
VIN IN OUT
( )VOUT = VFB 1 +
1µF
R1
R2
+ IFB R1
1µF
LT1118
R1
EN GND FB
R2
1118 TA06
U
OPERATIO
Output Capacitor
The LT1118 family of voltage regulators require an output
capacitor for stability. The regulators are stable with
output capacitors larger than 0.2µF. 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 0.2µF 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 0.1µF ceramic capaci-
tor 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 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
5
5 Page | ||
| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet LT1118-2.5.PDF ] | |
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