LX8820-33CLM データシートの表示（PDF） - Microsemi Corporation
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LX8820-33CLM Datasheet PDF : 6 Pages
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LX8820
®
3.3V/1.0A Ultra Low Dropout Regulator
TM
PRODUCTION DATA SHEET
APPLICATION INFORMATION
Description
The LX8820 is part of a family of LDO (Low Drop-Out) linear
regulators in the JEDEC MO-229 package that offer maximum
power dissipation in a low profile surface mount technology. The
LX8820 output is fixed at 3.3V output and can supply up to one
amp with a regulator design optimized for system efficiency by
consuming minimal ground current and directing quiescent current
to the load.
Input Capacitor
To improve load transient response and noise rejection an input
bypass capacitor of at least 2.2µF is required. Generally we
recommend a 4.7µF ceramic or tantalum or 22µF electrolytic
capacitor.
Output Capacitor
The regulator requires an output capacitor connected between VOUT
to GND to stabilize the internal control loop. Many types of
capacitors are available, with different capacitance values
tolerances, temperature coefficients and equivalent series
resistance. We recommend a minimum of 4.7µF. 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 0.01 to 2 ohms. We have found it best to use
the same type of capacitor for both input and output bypass.
Minimum Load Requirement
The LX8820 has a minimum load requirement for proper output
regulation specified at 0.1mA.
Temperature Protection
The thermal protection shuts the LX8820 down when the junction
temperature exceeds 140°C. Exposure to absolute maximum rated
conditions for extended periods may affect device reliability (see
Thermal Considerations below).
Current Limit Protection
The LX8820 includes over current protection. When the output
load current exceeds typically 1.5A, the circuit forces the regulator
output to decrease.
Thermal Considerations
Thermal shutdown protects the integrated circuit from thermal
overload caused from a rise in junction temperature during power
dissipation. 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 dose not exceed
it’s maximum rating. Operating 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.
Power dissipation for the regulator can be calculated using the
following equation:
PD = (VIN(MAX) - VOUT ) • IOUT
(Note: power dissipation resulting from quiescent (ground)
current is negligible)
Junction temperature of the integrated circuit can be calculated
using:
TJUNCTION = TJUNCTION-TAB RISE + TTAB-AMB RISE + TAMB
TTAB = PD MAX • ΘJT
TTAB-AMB = PD REG • ΘPCB
An example: Given conditions: TA = 70°C, VIN= 5.0V, Vout=
3.3V, Iout= 200mA.
Calculated values:
TJ-TAB REG = (5V - 3.3V) • (200mA) • 8°C/W
= (340mW) • 8°C/W = 2.7°C
TTAB-AMB RISE = (340mW) • 32°C/W = 10.9°C
TJUNCTION = 2.7°C + 10.9°C + 70°C = 83.6°C
It is important to note that although each output of the regulator
will produce up to 1.5A in current, the total power dissipation may
limit the useful total current draw. The junction temperature
should be calculated to insure the maximum junction temperature
is not exceeded.
Copyright © 2004
Rev. 1.1, 2005-02-24
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 5
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