MC33275, NCV33275
APPLICATIONS INFORMATION
V
in
V
ou
t
C
in
C
out
LOAD
GND
Figure 15. Typical Application Circuit
ESR (ohm)
The MC33275 regulators are designed with internal
current limiting and thermal shutdown making them
user−friendly. Figure 15 is a typical application circuit. The
output capability of the regulator is in excess of 300 mA,
with a typical dropout voltage of less than 260 mV. Internal
protective features include current and thermal limiting.
EXTERNAL CAPACITORS
100
V
out
= 3.0 V
C
out
= 1.0
mF
C
in
= 1.0
mF
10
Stable Region
1.0
These regulators require only a 0.33
mF
(or greater)
capacitance between the output and ground for stability for
1.8 V, 2.5 V, 3.0 V, and 3.3 V output voltage options. Output
voltage options of 5.0 V require only 0.22
mF
for stability.
The output capacitor must be mounted as close as possible
to the MC33275. If the output capacitor must be mounted
further than two centimeters away, then a larger value of
output capacitor may be required for stability. A value of
0.68
mF
or larger is recommended. Most type of aluminum,
tantalum, or multilayer ceramic will perform adequately.
Solid tantalums or appropriate multilayer ceramic
capacitors are recommended for operation below 25°C. An
input bypass capacitor is recommended to improve transient
response or if the regulator is connected to the supply input
filter with long wire lengths, more than 4 inches. This will
reduce the circuit’s sensitivity to the input line impedance at
high frequencies. A 0.33
mF
or larger tantalum, mylar,
ceramic, or other capacitor having low internal impedance
at high frequencies should be chosen. The bypass capacitor
should be mounted with shortest possible lead or track
length directly across the regulator’s input terminals.
Figure 16 shows the ESR that allows the LDO to remain
stable for various load currents.
0.1
0
50
100
150
200
250
300
LOAD CURRENT (mA)
Figure 16. ESR for V
out
= 3.0V
Applications should be tested over all operating
conditions to insure stability.
THERMAL PROTECTION
Internal thermal limiting circuitry is provided to protect
the integrated circuit in the event that the maximum junction
temperature is exceeded. When activated, typically at
150°C, the output is disabled. There is no hysteresis built
into the thermal protection. As a result the output will appear
to be oscillating during thermal limit. The output will turn
off until the temperature drops below the 150°C then the
output turns on again. The process will repeat if the junction
increases above the threshold. This will continue until the
existing conditions allow the junction to operate below the
temperature threshold.
Thermal limit is not a substitute for proper
heatsinking.
The internal current limit will typically limit current to
450 mA. If during current limit the junction exceeds 150°C,
the thermal protection will protect the device also.
Current
limit is not a substitute for proper heatsinking.
OUTPUT NOISE
In many applications it is desirable to reduce the noise
present at the output. Reducing the regulator bandwidth by
increasing the size of the output capacitor will reduce the noise.
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