LM4140ACM-1.2 National Semiconductor, LM4140ACM-1.2 Datasheet - Page 9

• Manufacturer Part Number: LM4140ACM-1.2
• Description: IC,VOLT REFERENCE,FIXED,1.25V,SOP,8PIN,PLASTIC
• Manufacturer: National Semiconductor

Specifications of LM4140ACM-1.2

• Rohs Compliant: NO

Application Hints
INPUT CAPACITORS
Although not always required, an input capacitor is recom-
mended. A supply bypass capacitor on the input assures that
the reference is working from a source with low impedance,
which improves stability. A bypass capacitor can also im-
prove transient response by providing a reservoir of stored
energy that the reference can utilize in case where the load
current demand suddenly increases. The value used for C
may be used without limit. Refer to the typical application
section for examples of input capacitors.
OUTPUT CAPACITORS
The LM4140 requires a 1µF (nominally) output capacitor for
loop stability (compensation) as well as transient response.
During the sudden changes in load current demand, the
output capacitor must source or sink current during the time
it takes the control loop of the LM4140 to respond.
This capacitor must be selected to meet the requirements of
minimum capacitance and equivalent series resistance
(ESR) range.
In general, the capacitor value must be at least 0.2µF (over
the actual ambient operating temperature), and the ESR
must be within the range indicated in Figure 1, Figure 2 and
Figure 3.
FIGURE 1. 0.22 µF ESR Range
FIGURE 2. 1 µF ESR Range
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TANTALUM CAPACITORS
Surface-mountable solid tantalum capacitors offer a good
combination of small physical size for the capacitance value,
and ESR in the range needed for by the LM4140. The results
of testing the LM4140 stability with surface mount solid
tantalum capacitors show good stability with values in the
range of 0.1µF. However, optimum performance is achieved
with a 1µF capacitor.
Tantalum capacitors that have been verified as suitable for
use with the LM4140 are shown in Table 1.
ALUMINUM ELECTROLYTIC CAPACITORS
Although probably not a good choice for a production design,
because of relatively large physical size, an aluminium elec-
trolytic capacitor can be used in the design prototype for an
LM4140 reference. A 1µF capacitor meeting the ESR condi-
tions can be used. If the operating temperature drops below
0˚C, the reference may not remain stable, as the ESR of the
aluminium electrolytic capacitor will increase, and may ex-
ceed the limits indicated in the figures.
TABLE 1. Surface-Mount Tantalum Capacitor Selection
Manufacturer
Siemens
Nichicon
Siemens
Nichicon
Sprague
Sprague
Kemet
Kemet
2.2µF Surface-Mount Tantalums
NEC
NEC
1µF Surface-Mount Tantalums
FIGURE 3. 10 µF ESR Range
Guide
293D105X0016A2T
293D225X0010A2T
T491A105M010AS
T491A225M010AS
B45196/2.2/10/10
B45196-E3105-K
Part Number
F931C105MA
F930J225MA
NRU225M06
NRU105N10
10107930
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