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LX8819

Dual Channel 1A Low Dropout Regulator

Microsemi Corporation 

LX8819

TM

®

Dual Channel 1A Low Dropout Regulator

DATA SHEET

APPLICATION INFORMATION

DESCRIPTION

The LX8819 is part of a family of Dual LDO (Low

Drop-Out) linear regulators in Microsemi’s S-PAK power

package which offer maximum power dissipation in a low

profile surface mount technology. The family includes a

combination of fixed and adjustable versions. Each

channel can supply up to one amp independently with a

regulator design optimized for system efficiency by

consuming minimal ground current and directing quiescent

current to the load.

VIN

LX8819

VOUT2

VOUT1

ADJ

R1

I

ADJ

1A

VOUT1 =

VREF

⋅

⎜⎜⎝⎛1 +

R1

R2

⎟⎟⎠⎞

+

IADJ

⋅R1

V

REF

R2

INPUT CAPACITOR

To improve load transient response and noise rejection

an input bypass capacitor of at least 2.2µF is required.

Generally it is recommended that a 20µF ceramic/tantalum

or 22µF electrolytic capacitor be used.

OUTPUT CAPACITOR

The LX8819 regulator requires output capacitors

connected between each voltage output and ground to

stabilize the internal control loop. Many types of

capacitors, with different capacitance values, tolerances,

temperature coefficients, and equivalent series resistance

are available for use with the LX8819. It is recommended

that a minimum of 4.7µF be used at each voltage output.

To ensure good transient response from the power

supply system under rapidly changing current load

conditions, designers generally use additional 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. The regulator has been tested stable with

capacitor ESR’s in the range of 50mΩ to 2Ω. It is

generally best to use the same type of capacitors for both

input and output bypassing.

ADJUSTABLE OUTPUT VOLTAGE

The LX8819 develops a 1.25V reference voltage

between the adjust terminal and ground (See Figure 2). By

placing a resistor, R2, between these two terminals, a

constant current is caused to flow through R1 and down

through R2 to set the overall output voltage. Because IADJ

is very small and constant when compared with the current

through R2, it represents a small error and can usually be

ignored.

MINIMUM LOAD REQUIREMENT

The LX8819 has a minimum load requirement for

proper output regulation. This minimum current is

specified at 0mA for the fixed output and 2mA for the

adjustable output regulator.

Figure 2 – Basic Regulator Circuit

TEMPERATURE PROTECTION

The thermal protection shuts the LX8819 down when the

junction temperature exceeds 140°C. Each output has

independent thermal shutdown capability. Exposure to

absolute maximum rated conditions for extended periods

may affect device reliability (See Thermal Considerations

below).

CURRENT LIMIT PROTECTION

The LX8819 includes over current protection. When the

output load current exceeds 1.4A (typical) the current limit

protection circuit forces the regulator to decrease the output

current in order to maintain safe levels.

THERMAL CONSIDERATIONS

Thermal shutdown protection circuitry protects the

integrated circuit from thermal overload caused from a rise

in junction temperature during excessive power dissipation

conditions. This means of protection is intended for fault

protection only and not as a means of current or power

limiting during normal application usage.

Proper thermal evaluation should be done to ensure that

the junction temperature (TJ) does not exceed its maximum

rating. Continuous operation at the maximum TJ of 150°C

can impact reliability.

Due to variation in individual device electrical

characteristics and thermal resistance, the built in thermal

overload protection may be activated at power levels

slightly above or below the rated dissipation. Also, peak

output power should be considered for each individual

output.

Total power dissipation for the regulator can be

calculated using the following equation:

( ) ( ) PD = VIN(MAX) − VOUT1 ⋅ IOUT1 + VIN(MAX) − VOUT2 ⋅ IOUT2

(Note: Power dissipation resulting from quiescent (ground)

current is negligible and ignored)

Copyright © 2003

Revision 1.0a, 4/29/2005

Microsemi

Integrated Products Division

11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570

Page 5

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