300mA CMOS L.D.O. Regulator

LM1108

Detail Description

HTC

- 3 -

- The LM1108 is aprecision, fixed output LDO.

Un like bipolar regulators, the LM1108’s supply current does not increase with load current.

range, (an important consideration in RTC and CMOS RAM battery back-up applications).

Figure3-1shows a typical application circuit.

1. Output Capacitor

The output capacitor should have an effective series resistance greater than 0.1Ω and less than .0Ω.

regulator and the AC filter capacitor or if a battery is used as the power source. Aluminum electrolytic or

tantalum capacitor types can be used. (Since many aluminum electrolytic capacitors freeze at approximately

-30°C, solid tantalums are recommended for applications operating below -25°C)

When operating from sources other than batteries,supply-noise rejection and transient response can be

improved by increasing the value of the input and output capacitors and employing passive filtering

techniques.

2. THERMAL CONSIDERATIONS

2.1 Thermal Shutdown

Integrated thermal protection circuitry shuts the regulator off when die temperature exceeds150°C.

The regulator remains off until the die temperature drops to approximately 140°C.

2.2 Power Dissipation

The amount of power the regulator dissipate is primarily a function of input and output voltage, and output

current. The following equation is used to calculate worst case actual power dissipation:

EQUATION 2-1:

TABLE 2-1 :

The maximum allowable power dissipation (Equation 2-2)

thermal resistance from junction-to-air(θJA).