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IMP37

Low Dropout Positive Voltage Regulators

IMP, Inc 

IMP37

Application Information

The IMP37 voltage regulator ICs offer self-protection features

which include short-circuit current protection and automatic thermal

shutdown (for junction temperature above 165°C).

Circuit Stability

Like all regulators, an output filter capacitor is required for circuit sta-

bility. Besides smoothing the output, the output capacitor

“completes” the regulator’s frequency compensation. The ESR of the

output capacitor should be less than 0.5Ω. Low ESR capacitors are

preferred.

Table 1 shows recommended minimum capacitance values for both

aluminum and tantalum capacitors. Larger values of output capaci-

tance do not cause stability problems.

Table 1. Recommended Output Bypass Capacitors

Output Bypass Capacitor (ESR < 0.5Ω)

10µF Tantalum, 100µF Aluminum

An input bypass capacitor is recommended. A 10µF or larger tanta-

lum capacitor is suitable for most applications.

Thermal Management

The maximum operating junction temperature for the IMP37 devices

is 150°C. The junction temperature can be calculated when the

power dissipation and ambient temperature are known with this

equation: TJ = TA + (PD x ΘJA).

The thermal resistance from juntion-to-ambient (ΘJA) is the sum of

the three thermal resistances:

ΘJA = ΘJT + ΘTS + ΘSA

Where ΘJT = Junction-to-Tab thermal resistance

ΘTS = Tab-to-Heat Sink thermal resistance

ΘSA = Heat Sink-to-Air thermal resistance

Table 2. Thermal Resistance of Packages

Package Type

SOT-223

Thermal Resistance

Junction to Tab, ΘJT

15°C/W

TO-263

10°C/W

The IMP37 series devices have thermal limiting circuitry to protect

the device from over current. For continuous operation, the maxi-

mum junction temperature rating must not be exceeded.

IMP37

VIN

+

*

IN

OUT

GND

+

**

3.3V

* Min. 15µF Tantalum or 100µF Aluminum.

Capacitor May Be Increased Without Limit.

** 10µF Tantalum or 100µF Aluminum

37_02.eps

Figure 1. Fixed 3.3V Regulator

4

408-432-9100/www.impweb.com

© 1999 IMP, Inc.

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