LT1585A-1.5 Linear Technology, LT1585A-1.5 Datasheet - Page 4

• Manufacturer Part Number: LT1585A-1.5
• Description: Fixed 1.5V/ 4.6A and 5A Low Dropout/ Fast Response GTL+ Regulators
• Manufacturer: Linear Technology

SI PLIFIED SCHE ATIC
LT1585-1.5/LT1585A-1.5
APPLICATIONS
General
The LT1585-1.5/LT1585A-1.5 3-terminal regulators are
easy to use and have all the protection features expected
in high performance linear regulators. The devices are
short-circuit protected, safe-area protected and provide
thermal shutdown to turn off the regulators if the junction
temperature exceeds about 150 C.
The ICs are pin compatible with the LT1083/LT1084/LT1085
family of linear regulators but offer lower dropout voltage
and faster transient response. The trade-off for this im-
proved performance is a 7V maximum supply voltage.
Similar to the LT1083/LT1084/LT1085 family, the LT1585-
1.5/LT1585A-1.5 regulators require an output capacitor for
stability. However, the improved frequency compensation
permits the use of capacitors with much lower ESR while still
maintaining stability. This is critical in addressing the needs
of modern low voltage, high speed microprocessors.
Current generation microprocessors and their associated
circuitry cycle load current from almost zero to several
amps in tens of nanoseconds. Output voltage tolerances
are tighter and include transient response as part of the
specification. The LT1585-1.5/LT1585A-1.5 are specifi-
cally designed to meet the fast current load step require-
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ments of these applications and save total cost by needing
less output capacitance in order to maintain regulation.
Stability
The circuit design in the LT1585-1.5/LT1585A-1.5 re-
quires the use of an output capacitor as part of the
frequency compensation. For all operating conditions, the
addition of a 22 F solid tantalum or a 100 F aluminum
electrolytic on the output ensures stability. Normally, the
LT1585-1.5/LT1585A-1.5 can use smaller value capaci-
tors. Many different types of capacitors are available and
have widely varying characteristics. These capacitors differ
in capacitor tolerance (sometimes ranging up to 100%),
equivalent series resistance, equivalent series inductance
and capacitance temperature coefficient. The LT1585-1.5/
LT1585A-1.5 frequency compensation optimizes frequency
response with low ESR capacitors. In general, use capaci-
tors with an ESR of less than 1 .
Normally, capacitor values on the order of several hundred
microfarads are used on the output of the regulators to
ensure good transient response with heavy load current
changes. Output capacitance can increase without limit
and larger values of output capacitance further improve the
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1585-1.5 SS
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