MIC5207 datasheet(11/24 Pages) MICROCHIP

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DS20005719C-page 11

MIC5207

4.0

APPLICATIONS INFORMATION

4.1

Enable/Shutdown

Forcing EN (enable/shutdown) high (> 2V) enables the

regulator. EN is compatible with CMOS logic gates.

If the enable/shutdown feature is not required, connect

EN (pin 3) to IN (supply input, pin 1). See Figure 4-1.

4.2

Input Capacitor

A 1 µF capacitor should be placed from IN to GND if

there is more than 10 inches of wire between the input

and the AC filter capacitor or if a battery is used as the

input.

4.3

Reference Bypass Capacitor

Reference bypass (BYP) is connected to the internal

voltage reference. A 470 pF capacitor (CBYP)

connected from BYP to GND quiets this reference,

providing a significant reduction in output noise. CBYP

reduces the regulator phase margin; when using CBYP,

output capacitors of 2.2 µF or greater are generally

required to maintain stability.

The start-up speed of the MIC5207 is inversely

proportional to the size of the reference bypass

capacitor. Applications requiring a slow ramp-up of

output voltage should consider larger values of CBYP.

Likewise, if rapid turn-on is necessary, consider

omitting CBYP.

If output noise is not a major concern, omit CBYP and

leave BYP open.

4.4

Output Capacitor

An output capacitor is required between OUT and GND

to prevent oscillation. The minimum size of the output

capacitor is dependent upon whether a reference

bypass capacitor is used. 1.0 µF minimum is

recommended when CBYP is not used (see Figure 4-2).

2.2 µF minimum is recommended when CBYP is 470 pF

(see Figure 4-1). Larger values improve the regulator’s

transient response. The output capacitor value may be

increased without limit.

The output capacitor should have an ESR (effective

series resistance) of about 5Ω or less and a resonant

frequency above 1 MHz. Ultra-low-ESR (ceramic)

capacitors can cause a low amplitude oscillation on the

output and/or under-damped transient response. Most

tantalum or aluminum electrolytic capacitors are

adequate; film types will work, but are more expensive.

Since many aluminum electrolytics have electrolytes

that freeze at about –30°C, solid tantalums are

recommended for operation below –25°C.

At lower values of output current, less output

capacitance is required for output stability. The

capacitor can be reduced to 0.47 µF for current below

10 mA or 0.33 µF for currents below 1 mA.

4.5

No-Load Stability

The MIC5207 will remain stable and in regulation with

no load (other than the internal voltage divider) unlike

many other voltage regulators. This is especially

important in CMOS RAM keep-alive applications.

4.6

Thermal Considerations

The MIC5207 is designed to provide 180 mA of

continuous current in a very small package. Maximum

power dissipation can be calculated based on the

output current and the voltage drop across the part. To

determine the maximum power dissipation of the

package, use the junction-to-ambient thermal

resistance of the device and the following basic

equation shown in Equation 4-1:

EQUATION 4-1:

TJ(MAX) is the maximum junction temperature of the

die, +125°C, and TA is the ambient operating

temperature. θJA is layout dependent; Table 4-1 shows

examples of junction-to-ambient thermal resistance for

the MIC5207.

The actual power dissipation of the regulator circuit can

be determined using Equation 4-2:

EQUATION 4-2:

Substituting PD(MAX) for PD and solving for the

operating conditions that are critical to the application

will give the maximum operating conditions for the

regulator circuit. For example, when operating the

TABLE 4-1:

SOT-23-5 THERMAL

RESISTANCE

θJA Rec.

Min. Footprint

θJA 1” Square

Copper Clad

θJ/C

235°C/W

170°C/W

130°C/W

PD MAX





TJ MAX





–





JA

-------------------------------------

VIN VOUT

–





IOUT



VIN

IGND



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