LX8587-XXCDD MICROSEMI [Microsemi Corporation], LX8587-XXCDD Datasheet - Page 5

• Manufacturer Part Number: LX8587-XXCDD
• Description: 3A Low Dropout Positive Regulators
• Manufacturer: MICROSEMI [Microsemi Corporation]

Copyright © 2000
Rev. 2.0a, 2005-10-25
(LDO) voltage regulators. They have all of the standard self-
protection features expected of a voltage regulator: short circuit
protection, safe operating area protection and automatic thermal
shutdown if the device temperature rises above approximately
165°C.
LX8587/87A series. Please see the table below for recommended
minimum capacitor values.
voltage tolerance and superior reference stability when measured
against the older pin-compatible regulator types that they replace.
STABILITY
compensation system. Many types of capacitors are available,
with
temperature coefficients, and equivalent series impedances. For
all operating conditions, connection of a 220µF aluminum
electrolytic capacitor or a 47µF (<400mΩ ESR) solid tantalum
capacitor between the output terminal and ground will guarantee
stable operation.
adjust (ADJ) pin and ground, ripple rejection will be improved
(please see the section entitled “RIPPLE REJECTION”). When
ADJ pin bypassing is used, the required output capacitor value
increases. Output capacitor values of 220µF (aluminum) or 47µF
(tantalum) provide for all cases of bypassing the ADJ pin. If an
ADJ pin bypass capacitor is not used, smaller output capacitor
values are adequate. The table below shows recommended
minimum capacitance values for operation.
system under rapidly changing current load conditions, designers
generally use several output capacitors connected in parallel.
Such an arrangement serves to minimize the effects of the
parasitic resistance (ESR) and inductance (ESL) that are present
in all capacitors. Cost-effective solutions that sufficiently limit
ESR and ESL effects generally result in total capacitance values
in the range of hundreds to thousands of microfarads, which is
more than adequate to meet regulator output capacitor
specifications. Output capacitance values may be increased
without limit.
transient response characteristics of the regulator in a power
system under changing loads. The effects of different capacitor
types and values on transient response parameters, such as
overshoot and under-shoot, can be compared quickly in order to
develop an optimum solution.
Use of an output capacitor is REQUIRED with the
INPUT
The LX8587/87A Series ICs are easy to use Low-Dropout
These regulators offer a more tightly controlled reference
The output capacitor is part of the regulator’s frequency
If a bypass capacitor is connected between the output voltage
To ensure good transient response from the power supply
The circuit shown in Figure 1 can be used to observe the
10µF
10µF
TM
different
Minimum Capacitor Values
15µF Tantalum, 100µF Aluminum
47µF Tantalum, 220µF Aluminum
capacitance
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: [phone]
OUTPUT
value
tolerances,
A P P L I C A T I O N N O T E S
capacitance
Integrated Products
®
None
ADJ
15µF
Microsemi
OVERLOAD RECOVERY
regulators are equipped with Safe Operating Area (SOA)
protection. The SOA circuit limits the regulator's maximum
output current to progressively lower values as the input-to-output
voltage difference increases. By limiting the maximum output
current, the SOA circuit keeps the amount of power that is
dissipated in the regulator itself within safe limits for all values of
input-to-output voltage within the operating range of the
regulator. The LX8587/87A SOA protection system is designed
to be able to supply some output current for all values of input-to-
output voltage, up to the device breakdown voltage.
prevent a power supply system from returning to regulated opera-
tion after removal of an intermittent short circuit at the output of
the regulator. This is a normal mode of operation, which can be
seen, in most similar products, including older devices such as
7800 series regulators. It is most likely to occur when the power
system input voltage is relatively high and the load impedance is
relatively low.
output voltages are very close to zero. The output voltage closely
follows the rising input voltage, and the input-to-output voltage
difference is small. The SOA circuit therefore permits the
regulator to supply large amounts of current as needed to develop
the designed voltage level at the regulator output.
regulated voltage to a resistive load under steady state conditions.
A moderate input-to-output voltage appears across the regulator
but the voltage difference is small enough that the SOA circuitry
allows sufficient current to flow through the regulator to develop
the designed output voltage across the load resistance. If the
output resistor is short-circuited to ground, the input-to-output
voltage difference across the regulator suddenly becomes larger
by the amount of voltage that had appeared across the load
resistor. The SOA circuit reads the increased input-to-output
voltage, and cuts back the amount of current that it will permit the
regulator to supply to its output terminal. When the short circuit
across the output resistor is removed, all the regulator output
current will again flow through the output resistor. The maximum
current that the regulator can supply to the resistor will be limited
by the SOA circuit, based on the large input-to-output
3A Low Dropout Positive Regulators
Supply
Power
Like almost all IC power regulators, the LX8587/87A
Under some conditions, a correctly operating SOA circuit may
When the power system is started “cold”, both the input and
Now consider the case where the regulator is supplying
FIGURE 1 - DYNAMIC INPUT AND OUTPUT TEST
P
RODUCTION
IN
ADJ
Star Ground
D
ATA
OUT
S
HEET
(Larger resistor)
Minimum Load
LX8587x-xx
10ms
R
Full Load
DSON
(Smaller
resistor)
<< R
1 sec
L
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