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參數(shù)資料
| 型號： | LM4132AMFX-4.1 |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 基準電壓源/電流源 |
| 英文描述： | SOT-23 Precision Low Dropout Voltage Reference |
| 中文描述： | 4.1 V FIXED POSITIVE LDO REGULATOR, 0.4 V DROPOUT, PDSO5 |
| 封裝： | SOT-23, 5 PIN |
| 文件頁數(shù)： | 11/15頁 |
| 文件大?。?/td> | 863K |
| 代理商： | LM4132AMFX-4.1 |
Application Information
THEORY OF OPERATION
The foundation of any voltage reference is the band-gap
circuit. While the reference in the LM4132 is developed from
the gate-source voltage of transistors in the IC, principles of
the band-gap circuit are easily understood using a bipolar
example. For a detailed analysis of the bipolar band-gap
circuit, please refer to Application Note AN-56.
SUPPLY AND ENABLE VOLTAGES
To ensure proper operation, V
EN
and V
IN
must be within a
specified range. An acceptable range of input voltages is
V
IN
>
V
REF
+ 400mV (I
LOAD
≤
10mA)
The enable pin uses an internal pull-up current source (I
P-
ULL_UP
)
2μA) that may be left floating or triggered by an
external source. If the part is not enabled by an external
source, it may be connected to V
. An acceptable range of
enable voltages is given by the enable transfer characteris-
tics. See the Electrical Characteristics section and Enable
Transfer Characteristics figure for more detail. Note, the part
will not operate correctly for V
EN
>
V
IN
.
COMPONENT SELECTION
Asmall ceramic (X5R or X7R) capacitor on the input must be
used to ensure stable operation. The value of C
must be
sized according to the output capacitor value. The value of
C
must satisfy the relationship C
≥
C
. When no output
capacitor is used, C
must have a minimum value of 0.1μF.
Noise on the power-supply input may affect the output noise.
Larger input capacitor values (typically 4.7μF to 22μF) may
help reduce noise on the output and significantly reduce
overshoot during startup. Use of an additional optional by-
pass capacitor between the input and ground may help
further reduce noise on the output. With an input capacitor,
the LM4132 will drive any combination of resistance and
capacitance up to V
REF
/20mA and 10μF respectively.
The LM4132 is designed to operate with or without an output
capacitor and is stable with capacitive loads up to 10μF.
Connecting a capacitor between the output and ground will
significantly improve the load transient response when
switching from a light load to a heavy load. The output
capacitor should not be made arbitrarily large because it will
effect the turn-on time as well as line and load transients.
While a variety of capacitor chemistry types may be used, it
is typically advisable to use low esr ceramic capacitors. Such
capacitors provide a low impedance to high frequency sig-
nals, effectively bypassing them to ground. Bypass capaci-
tors should be mounted close to the part. Mounting bypass
capacitors close to the part will help reduce the parasitic
trace components thereby improving performance.
SHORT CIRCUITED OUTPUT
The LM4132 features indefinite short circuit protection. This
protection limits the output current to 75mA when the output
is shorted to ground.
TURN ON TIME
Turn on time is defined as the time taken for the output
voltage to rise to 90% of the preset value. The turn on time
depends on the load. The turn on time is typically 33.2μs
when driving a 1μF load and 78.8μs when driving a 10μF
load. Some users may experience an extended turn on time
(up to 10ms) under brown out conditions and low tempera-
tures (-40C).
THERMAL HYSTERESIS
Thermal hysteresis is the defined as the change in output
voltage at 25
o
C after some deviation from 25
o
C. This is to
say that thermal hysteresis is the difference in output voltage
between two points in a given temperature profile. An illus-
trative temperature profile is shown in Figure 1.
This may be expressed analytically as the following:
Where
V
HYS
= Thermal hysteresis expressed in ppm
V
REF
= Nominal preset output voltage
V
REF1
= V
REF
before temperature fluctuation
V
REF2
= V
REF
after temperature fluctuation.
The LM4132 features a low thermal hysteresis of 75 ppm
(typical) from -40C to 125C after 8 temperature cycles.
TEMPERATURE COEFFICIENT
Temperature drift is defined as the maximum deviation in
output voltage over the operating temperature range. This
deviation over temperature may be illustrated as shown in
Figure 2.
Temperature coefficient may be expressed analytically as
the following:
20151338
FIGURE 1. Illustrative Temperature Profile
20151339
FIGURE 2. Illustrative V
REF
vs Temperature Profile
L
www.national.com
11
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