LT1587-1.5 Linear Technology, LT1587-1.5 Datasheet - Page 4

• Manufacturer Part Number: LT1587-1.5
• Description: Fixed 1.5V/ 3A Low Dropout Fast Response GTL + Regulator
• Manufacturer: Linear Technology

SI PLIFIED SCHE ATIC
LT1587-1.5
APPLICATIONS
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General
The LT1587-1.5 3-terminal regulator is easy to use and
has all the protection features expected in a high perfor-
mance linear regulator. The device is short-circuit pro-
tected, safe-area protected and provides thermal shut-
down to turn off the regulator if the junction temperature
exceeds about 150 C.
The IC is pin compatible with the LT1083/LT1084/LT1085
family of linear regulators but offers 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 LT1587-
1.5 regulator requires 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 LT1587-1.5 is specifically designed to
meet the fast current load step requirements of these
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applications and saves total cost by needing less output
capacitance in order to maintain regulation.
Stability
The circuit design in the LT1587-1.5 requires 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 LT1587-1.5 can use smaller
value capacitors. Many different types of capacitors are
available and have widely varying characteristics. These
capacitors differ in capacitor tolerance (sometimes rang-
ing up to 100%), equivalent series resistance, equivalent
series inductance and capacitance temperature coefficient.
The LT1587-1.5 frequency compensation optimizes fre-
quency response with low ESR capacitors. In general, use
capacitors 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
stability and transient response of the LT1587-1.5.
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