TC2117

DS21665B-page 4

© 2002 Microchip Technology Inc.

3.0

DETAILED DESCRIPTION

The TC2117 is a precision, positive output LDO. Unlike

bipolar regulators, the TC2117 supply current does not

increase proportionally with load current. In addition,

entire 0mA to 800mA operating load range.

FIGURE 3-1:

TYPICAL APPLICATION

CIRCUIT

3.1

Output Capacitor

A1

The output capacitor should have an effective series

resistance of 0.2

Ω to 10Ω.A 1µF capacitor should be

inches of wire between the 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 rec-

ommended for applications operating below -25°C.)

When operating from sources other than batteries, sup-

ply noise rejection and transient response can be

improved by increasing the value of the input and output

capacitors and employing passive filtering techniques.

3.2

Thermal Considerations

3.2.1

THERMAL SHUTDOWN

Integrated thermal protection circuitry shuts the regula-

tor off when die temperature exceeds 160°C. The reg-

ulator remains off until the die temperature drops to

approximately 150°C.

3.2.2

POWER DISSIPATION

The amount of power the regulator dissipates is prima-

rily a function of input and output voltage, and output

current. The following equation is used to calculate

worst case actual power dissipation:

EQUATION 3-1:

The

maximum

allowable

power

dissipation

(Equation 3-2) is a function of the maximum ambient

perature (125°C) and the thermal resistance from

junction-to-air (

EQUATION 3-2:

Table 3-1 shows various values of

mounted on a 1/16 inch, 2-layer PCB with 1 oz. copper

foil.

TABLE 3-1:

THERMAL RESISTANCE

GUIDELINES FOR TC2117 IN

3-PIN SOT-223 PACKAGE

C1

1

µF

Battery

TC2117

C2

1

µF

GND

Copper

Area

(Topside)*

Copper

Area

(Backside)

Board Area

Thermal

Resistance

2500 sq mm

2500 sq mm

2500 sq mm

45°C/W

1000 sq mm

2500 sq mm

2500 sq mm

45°C/W

225sqmm

2500sq mm

2500sq mm

53°C/W

100sqmm

2500sq mm

2500sq mm

59°C/W

1000 sq mm

1000 sq mm

1000 sq mm

52°C/W

1000 sq mm

0sqmm

1000sq mm

55°C/W

*Tab of device attached to topside copper.

Where:

Where all terms are previously defined.