LM2931Z-5.0 National Semiconductor, LM2931Z-5.0 Datasheet - Page 13

• Manufacturer Part Number: LM2931Z-5.0
• Description: IC, V REG LDO +5.0V, 2931, TO-92-3
• Manufacturer: National Semiconductor

Specifications of LM2931Z-5.0

• Primary Input Voltage: 14V
• Output Voltage: 5V
• Dropout Voltage Vdo: 300mV
• No. Of Pins: 3
• Output Current: 100mA
• Voltage Regulator Case Style: TO-92
• Operating Temperature Range: -40°C To +85°C
• Svhc: No
• Output Voltage Fixed: 5V
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Application Hints
One of the distinguishing factors of the LM2931 series regu-
lators is the requirement of an output capacitor for device
stability. The value required varies greatly depending upon
the application circuit and other factors. Thus some com-
ments on the characteristics of both capacitors and the
regulator are in order.
High frequency characteristics of electrolytic capacitors de-
pend greatly on the type and even the manufacturer. As a
result, a value of capacitance that works well with the
LM2931 for one brand or type may not necessary be suffi-
cient with an electrolytic of different origin. Sometimes actual
bench testing, as described later, will be the only means to
determine the proper capacitor type and value. Experience
has shown that, as a rule of thumb, the more expensive and
higher quality electrolytics generally allow a smaller value for
regulator stability. As an example, while a high-quality 100
µF aluminum electrolytic covers all general application cir-
cuits, similar stability can be obtained with a tantalum elec-
trolytic of only 47µF. This factor of two can generally be
applied to any special application circuit also.
Another critical characteristic of electrolytics is their perfor-
mance over temperature. While the LM2931 is designed to
operate to −40˚C, the same is not always true with all elec-
trolytics (hot is generally not a problem). The electrolyte in
many aluminum types will freeze around −30˚C, reducing
their effective value to zero. Since the capacitance is needed
for regulator stability, the natural result is oscillation (and lots
of it) at the regulator output. For all application circuits where
cold operation is necessary, the output capacitor must be
rated to operate at the minimum temperature. By coinci-
dence, worst-case stability for the LM2931 also occurs at
minimum temperatures. As a result, in applications where
the regulator junction temperature will never be less than
25˚C, the output capacitor can be reduced approximately by
a factor of two over the value needed for the entire tempera-
ture range. To continue our example with the tantalum elec-
trolytic, a value of only 22µF would probably thus suffice. For
high-quality aluminum, 47µF would be adequate in such an
application.
Another regulator characteristic that is noteworthy is that
stability decreases with higher output currents. This sensible
fact has important connotations. In many applications, the
LM2931 is operated at only a few milliamps of output current
or less. In such a circuit, the output capacitor can be further
reduced in value. As a rough estimation, a circuit that is
required to deliver a maximum of 10mA of output current
from the regulator would need an output capacitor of only
half the value compared to the same regulator required to
deliver the full output current of 100mA. If the example of the
tantalum capacitor in the circuit rated at 25˚C junction tem-
perature and above were continued to include a maximum of
10mA of output current, then the 22µF output capacitor could
be reduced to only 10µF.
In the case of the LM2931CT adjustable regulator, the mini-
mum value of output capacitance is a function of the output
voltage. As a general rule, the value decreases with higher
output voltages, since internal loop gain is reduced.
13
At this point, the procedure for bench testing the minimum
value of an output capacitor in a special application circuit
should be clear. Since worst-case occurs at minimum oper-
ating temperatures and maximum operating currents, the
entire circuit, including the electrolytic, should be cooled to
the minimum temperature. The input voltage to the regulator
should be maintained at 0.6V above the output to keep
internal power dissipation and die heating to a minimum.
Worst-case occurs just after input power is applied and
before the die has had a chance to heat up. Once the
minimum value of capacitance has been found for the brand
and type of electrolytic in question, the value should be
doubled for actual use to account for production variations
both in the capacitor and the regulator. (All the values in this
section and the remainder of the data sheet were deter-
mined in this fashion.)
LM2931 micro SMD Light Sensitivity
When the LM2931 micro SMD package is exposed to bright
sunlight, normal office fluorescent light, and other LED’s, it
operates within the guaranteed limits specified in the electri-
cal characteristic table.
Definition of Terms
Dropout Voltage: The input-output voltage differential at
which the circuit ceases to regulate against further reduction
in input voltage. Measured when the output voltage has
dropped 100 mV from the nominal value obtained at 14V
input, dropout voltage is dependent upon load current and
junction temperature.
Input Voltage: The DC voltage applied to the input terminals
with respect to ground.
Input-Output Differential: The voltage difference between
the unregulated input voltage and the regulated output volt-
age for which the regulator will operate.
Line Regulation: The change in output voltage for a change
in the input voltage. The measurement is made under con-
ditions of low dissipation or by using pulse techniques such
that the average chip temperature is not significantly af-
fected.
Load Regulation: The change in output voltage for a
change in load current at constant chip temperature.
Long Term Stability: Output voltage stability under accel-
erated life-test conditions after 1000 hours with maximum
rated voltage and junction temperature.
Output Noise Voltage: The rms AC voltage at the output,
with constant load and no input ripple, measured over a
specified frequency range.
Quiescent Current: That part of the positive input current
that does not contribute to the positive load current. The
regulator ground lead current.
Ripple Rejection: The ratio of the peak-to-peak input ripple
voltage to the peak-to-peak output ripple voltage at a speci-
fied frequency.
Temperature Stability of V
output voltage for a thermal variation from room temperature
to either temperature extreme.
O
: The percentage change in
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