MC33275, NCV33275

http://onsemi.com

8

APPLICATIONS INFORMATION

LOAD

t

GND

Figure 15. Typical Application Circuit

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

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

100

LOAD CURRENT (mA)

100

200

300

10

1.0

0.1

50

150

250

Stable Region

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.