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參數(shù)資料
| 型號： | LX8221-GIDUT |
| 英文描述： | Analog IC |
| 中文描述： | 模擬IC |
| 文件頁數(shù)： | 4/9頁 |
| 文件大?。?/td> | 211K |
| 代理商： | LX8221-GIDUT |
Microsemi
Linfinity Microelectronics Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 4
Copyright
2000
Rev. 1.0, 2002-01-02
W
M
.
C
LX8221
Dual 150mA CMOS Low Dropout Regulator
P
RODUCTION
A P P L I C A T I O N S
Description
The LX8221 family of LDO linear regulators is available
in a 10-pin MSOP Package and provides a cost effective
power management solution for battery driven applications.
The regulator family includes both fixed/adjustable and
adjustable/adjustable output voltage versions. The internal
PMOS power device provides low dropout regulation with
a fast line and load transient response. It also includes
internal current limiting and thermal shutdown circuitry. In
this section you will find information about capacitor,
thermal, and layout design considerations.
Input Capacitor
To improve load transient response and noise rejection a
bypass capacitor is recommended (but it is not required for
stability). There are no requirements for the ESR
(Equivalent Series Resistor) on the input capacitor, but
tolerance and temperature coefficient must be considered
when selecting this capacitor to ensure that the capacitor’s
value will be around 1
μ
F over the entire operating
temperature range. For the LX8221, a 1
μ
F ceramic type
capacitor may be connected between both VIN1/2 and
ground.
Output Capacitor
The LX8221 uses an internal feedback loop to maintain a
constant output voltage. This feedback loop induces a
natural phase shift and the amount of phase shift
determines the loop’s stability. Therefore, like any low-
dropout regulator, an output capacitor with low ESR
(Equivalent Series Resistance) is required between VOUT
and GND to stabilize the internal control loop. A ceramic,
tantalum or electrolytic capacitor with a minimum
recommended capacitance value of 1.0
μ
F and ESR
between 5m
and 1
will satisfy the stability for the entire
operating range.
Optional Bypass Capacitor
The fixed/adjustable voltage version of the LX8221
includes a separate Bypass pin (CB1) for the fixed
regulator that allows for further reduction of output noise.
If the regulator’s output noise performance meets system
design specifications without the capacitor, omit it. The
bypass capacitor impacts the start up time, which is
inversely proportional to the size of bypass capacitor.
Further, the bypass capacitor reduces the regulator phase
margin. Hence, implementing the bypass capacitor will
require the use of a larger output capacitor to maintain the
LDO’s stability. The LX8221-x adjustable regulator’s
output voltage can be externally set by connecting the ADJ
pin/s to an external resistor divider (See Figure 1 and 2).
The output voltage can be calculated using the formula:
+
=
2
1
ADJ
OUT
R
R
1
V
V
Enable
The Enable pin allows the LX8221 to be independently
turned on and off. The Enable pins are compatible with
standard TTL-CMOS levels. A logic zero (0.4V) on the En
1
/
En
2
pins shuts the LX8221 off and reduces the supply
current to less than 1
μ
A (typ). Pulling the Enable inputs high
(2.0V) causes normal operation to resume. If the Enable
feature is not used, this pin can be connected to V
IN
.
Minimum Load Requirement
Although line regulation is improved with a minimum load
of 100
μ
A, the LX8221 does not have a minimum load
current in order to maintain stability. This is an especially
important feature in certain applications.
Temperature Protection
The thermal protection shuts the LX8221 down when the
junction temperature exceeds approximately 150
0
C; there is
no appreciable thermal hysteresis.
Short Circuit Current Protection
The LX8221 includes over-current protection, when the
output load current exceeds about 400mA. When this
occurs, the protection circuit forces the regulator to decrease
its output current.
Thermal Consideration
Thermal shutdown protects the integrated circuit from
thermal overload caused from a rise in junction temperature
during power dissipation. This type 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 T
J
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. Power dissipation for each regulator can
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