LM4128CMF-1.8/NOPB National Semiconductor, LM4128CMF-1.8/NOPB Datasheet - Page 13

• Manufacturer Part Number: LM4128CMF-1.8/NOPB
• Description: IC REF MICROPWR 1.8V SOT23-5
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM4128CMF-1.8/NOPB

• Reference Type: Series
• Voltage - Output: 1.8V
• Tolerance: ±0.5%
• Temperature Coefficient: 100ppm/°C
• Voltage - Input: 2.2 ~ 5.5 V
• Number Of Channels: 1
• Current - Quiescent: 100µA
• Current - Output: 20mA
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: SOT-23-5, SC-74A, SOT-25
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Cathode: -
• Other names: LM4128CMF-1.8TR; LM4128CMF-1.8TR

Application Information
THEORY OF OPERATION
The foundation of any voltage reference is the band-gap cir-
cuit. While the reference in the LM4128 is developed from the
gate-source voltage of transistors in the IC, principles of the
band-gap circuit are easily understood using a bipolar exam-
ple. 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
specified range. An acceptable range of input voltages is
The enable pin uses an internal pull-up current source
(I
external source. If the part is not enabled by an external
source, it may be connected to V
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
COMPONENT SELECTION
A small ceramic (X5R or X7R) capacitor on the input must be
used to ensure stable operation. The value of C
sized according to the output capacitor value. The value of
C
capacitor is used, C
Noise on the power-supply input may affect the output noise.
Larger input capacitor values (typically 4.7 µF to 22 µF) may
help reduce noise on the output and significantly reduce over-
shoot during startup. Use of an additional optional bypass
capacitor between the input and ground may help further re-
duce noise on the output. With an input capacitor, the LM4128
will drive any combination of resistance and capacitance up
to V
The LM4128 is designed to operate with or without an output
capacitor and is stable with capacitive loads up to 10 µF.
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 ca-
pacitor 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 capacitors
should be mounted close to the part. Mounting bypass ca-
pacitors close to the part will help reduce the parasitic trace
components thereby improving performance.
SHORT CIRCUITED OUTPUT
The LM4128 features indefinite short circuit protection. This
protection limits the output current to 75 mA 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 33.2 µs when driving
a 1µF load and 78.8 µs when driving a 10 µF load. Some users
may experience an extended turn on time (up to 10 ms) under
brown out conditions and low temperatures (-40°C).
PULL_UP
IN
must satisfy the relationship C
REF
/20 mA and 10 µF respectively.
≊
V
2 µA) that may be left floating or triggered by an
IN
> V
REF
IN
must have a minimum value of 0.1 µF.
+ 400 mV (I
EN
EN
> V
IN
IN
LOAD
and V
. An acceptable range of
≥
IN
.
C
≤
OUT
IN
10 mA)
must be within a
. When no output
IN
must be
13
THERMAL HYSTERESIS
Thermal hysteresis is defined as the change in output voltage
at 25ºC after some deviation from 25ºC. This is to say that
thermal hysteresis is the difference in output voltage between
two points in a given temperature profile. An illustrative tem-
perature profile is shown in Figure 1.
This may be expressed analytically as the following:
Where
V
V
V
V
The LM4128 features a low thermal hysteresis of 190 µV from
-40°C to 125°C.
TEMPERATURE COEFFICIENT
Temperature drift is defined as the maximum deviation in out-
put voltage over the operating temperature range. This devi-
ation over temperature may be illustrated as shown in Figure
2.
Temperature coefficient may be expressed analytically as the
following:
HYS
REF
REF1
REF2
FIGURE 2. Illustrative Temperature Coefficient Profile
= Nominal preset output voltage
= Thermal hysteresis expressed in ppm
= V
= V
FIGURE 1. Illustrative Temperature Profile
REF
REF
before temperature fluctuation
after temperature fluctuation.
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