TC2117 datasheet(7/18 Pages) MICROCHIP

7 / 18 page

DS21665C-page 7

TC2117

4.0

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,

VOUT remains stable and within regulation over the

entire 0 mA to 800 mA operating load range.

FIGURE 4-1:

TYPICAL APPLICATION

CIRCUIT

4.1

Output Capacitor

A 1 µF (min) capacitor from VOUT to ground is required.

The output capacitor should have an effective series

resistance of 0.2

Ω to 10Ω. A 1 µF capacitor should be

connected from VIN to GND if there is more than 10

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

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.

4.2

Thermal Considerations

4.2.1

THERMAL SHUTDOWN

Integrated thermal protection circuitry shuts the regula-

tor off when die temperature exceeds 160°C. The

regulator remains off until the die temperature drops to

approximately 150°C.

4.2.2

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 4-1:

The

maximum

allowable

power

dissipation

(Equation 4-2) is a function of the maximum ambient

temperature (TAMAX), the maximum allowable die

temperature (+125°C) and the thermal resistance from

junction-to-air (

θJA).

EQUATION 4-2:

Table 4-1 shows various values of

θJA for the TC2117

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

foil.

TABLE 4-1:

THERMAL RESISTANCE

GUIDELINES FOR TC2117 IN

3-PIN SOT-223 PACKAGE

1µF

Battery

TC2117

VIN

VOUT

1µF

GND

VOUT

Copper

Area

(Topside)*

Copper

Area

(Backside)

Board Area

Thermal

Resistance

2500 sq mm

45°C/W

1000 sq mm

2500 sq mm

45°C/W

225 sq mm

2500 sq mm

53°C/W

100 sq mm

2500 sq mm

59°C/W

1000 sq mm

52°C/W

1000 sq mm

0 sq mm

1000 sq mm

55°C/W

* Tab of device attached to topside copper.

Where:

VINMAX

VOUTMIN

ILOADMAX

PD = Worst-case actual power dissipation

= Minimum regulator output voltage

= Maximum output (load) current

= Maximum voltage on VIN

VINMAX VOUTMIN

–

()I

LOADMAX

PDMAX = (TJMAX – TAMAX)

θJA

Where all terms are previously defined.

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