SM72238X/NOPB National Semiconductor, SM72238X/NOPB Datasheet - Page 9

• Manufacturer Part Number: SM72238X/NOPB
• Description: IC REG SOLARMAGIC 100MA TO-252-3
• Manufacturer: National Semiconductor
• Series: SolarMagic™r

Specifications of SM72238X/NOPB

• Regulator Topology: Positive Fixed
• Voltage - Output: 5V
• Voltage - Input: Up to 30V
• Voltage - Dropout (typical): 0.38V @ 100mA
• Number Of Regulators: 1
• Current - Output: 100mA
• Current - Limit (min): 160mA
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: *
• Package / Case: *
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Application Hints
EXTERNAL CAPACITORS
A 1.0μF (or greater) capacitor is required between the output
and ground for stability. Without this capacitor the part will
oscillate. Most types of tantalum or aluminum electrolytics
work fine here; even film types work but are not recommended
for reasons of cost. Many aluminum electrolytics have elec-
trolytes that freeze at about −30°C, so solid tantalums are
recommended for operation below −25°C. The important pa-
rameters of the capacitor are an ESR of about 5Ω or less and
a resonant frequency above 500kHz. The value of this ca-
pacitor may be increased without limit.
Ceramic capacitors whose value is greater than 1000pF
should not be connected directly from the SM72238 output to
ground. Ceramic capacitors typically have ESR values in the
range of 5 to 10mΩ, a value below the lower limit for stable
operation (see curve Output Capacitor ESR Range).
The reason for the lower ESR limit is that the loop compen-
sation of the part relies on the ESR of the output capacitor to
provide the zero that gives added phase lead. The ESR of
ceramic capacitors is so low that this phase lead does not
occur, significantly reducing phase margin. A ceramic output
Typical Applications
*Minimum input-output voltage ranges from 40mV to 400mV, depending on load current. Current limit is typically 160mA.
5 Volt Current Limiter
9
capacitor can be used if a series resistance is added (recom-
mended value of resistance about 0.1Ω to 2Ω).
At lower values of output current, less output capacitance is
required for stability. The capacitor can be reduced to
0.33μF for currents below 10mA or 0.1μF for currents below
1mA.
Unlike many other regulators, the SM72238 will remain stable
and in regulation with no load in addition to the internal voltage
divider. This is especially important in CMOS RAM keep-alive
applications.
A 1μF tantalum, ceramic or aluminum electrolytic capacitor
should be placed from the SM72238 input to ground if there
is more than 10 inches of wire between the input and the AC
filter capacitor or if a battery is used as the input.
REDUCING OUTPUT NOISE
In reference applications it may be advantageous to reduce
the AC noise present at the output. One method is to reduce
the regulator bandwidth by increasing the size of the output
capacitor. This is the only way noise can be reduced but is
relatively inefficient, as increasing the capacitor from 1μF to
220μF only decreases the noise from 430μV to 160μV rms for
a 100kHz bandwidth at 5V output.
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