LX8585-XX MICROSEMI [Microsemi Corporation], LX8585-XX Datasheet - Page 5

• Manufacturer Part Number: LX8585-XX
• Description: 4.6A Low Dropout Positive Regulators
• Manufacturer: MICROSEMI [Microsemi Corporation]

Copyright © 1997
Rev. 2.2a, 2005-11-10
(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.
series. Please see the table below for recommended minimum
capacitor values.
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
different capacitance value tolerances, capacitance temperature
coefficients, and equivalent series impedances. For all operating
conditions, connection of a 220μF aluminum electrolytic capacitor
or a 47μF 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 stable operation
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 undershoot, can be compared quickly in order to
develop an optimum solution.
The LX8585/85A Series ICs are easy to use Low-Dropout
Use of an output capacitor is REQUIRED with the LX8585/85A
These regulators offer a more tightly controlled reference voltage
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 system
The circuit shown in Figure 5 can be used to observe the
Input
10µF
10µF
TM
15µF Tantalum, 100µF Aluminum
47µF Tantalum, 220µF Aluminum
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: [phone]
Output
A P P L I C A T I O N N O T E
Integrated Products Division
None
15µF
Adj
®
Microsemi
4.6A Low Dropout Positive Regulators
OVERLOAD RECOVERY
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
LX8585/85A 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
operation 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 voltage
across the regulator at the time the short circuit is removed from
the output.
Power Supply
Like almost all IC power regulators, the LX8585/85A regulators
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 5 – Dynamic Input & Output Test
P
RODUCTION
IN
LX8585/85A
ADJ
LX8585-xx / LX858A-xx
Star Ground
D
ATA
OUT
S
HEET
Minumum Load
(Larger resistor)
Full Load
(Smaller resistor)
R
10ms
DSON
<< R
1 sec
L
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