MIC5209 datasheet(12/30 Pages) MICROCHIP

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MIC5209

DS20005720B-page 12

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2017 - 2022 Microchip Technology Inc. and its subsidiaries

4.0

APPLICATIONS INFORMATION

4.1

Enable/Shutdown

Enable is not available on devices in the SOT-223 (S)

package.

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

regulator. EN is compatible with CMOS logic. If the

enable/shutdown feature is not required, connect EN to

IN (supply input).

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

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 µF minimum is

recommended when CBYP is not used (see Figure 4-1).

2.2 µF minimum is recommended when CBYP is 470 pF

(see Figure 4-2). Larger values improve the regulator’s

transient response.

The output capacitor should have an ESR (equivalent

series resistance) of about 1Ω and a resonant

frequency above 1 MHz. Ultra-low-ESR and ceramic

capacitors can cause a low amplitude oscillation on the

output and/or underdamped 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 needed 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.

4.4

No-Load Stability

The MIC5209 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 CMOSRAM keep-alive applications.

4.5

Reference Bypass Capacitor

Reference bypass (BYP) is available only on devices in

SOIC-8 and DDPAK packages.

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 (ultra-low-noise performance). Because

CBYP reduces the phase margin, the output capacitor

should be increased to at least 2.2 µF to maintain

stability.

The start-up speed of the MIC5209 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.

4.6

Thermal Considerations

The SOT-223 has a ground tab that allows it to

dissipate more power than the SOIC-8 (refer to the

Slot-1 Power Supply sub-section for details). At +25°C

ambient, it will operate reliably at 1.6W dissipation with

“worst-case” mounting (no ground plane, minimum

trace widths, and FR4 printed circuit board).

Thermal resistance values for the SOIC-8 represent

typical mounting on a 1”-square, copper-clad, FR4

circuit board. For greater power dissipation, SOIC-8

versions of the MIC5209 feature a fused internal lead

frame and die bonding arrangement that reduces

thermal resistance when compared to standard SOIC-8

packages.

Multilayer boards with a ground plane, wide traces near

the pads, and large supply-bus lines will have better

thermal conductivity and will also allow additional

power dissipation.

For additional heat sink characteristics, refer to

Application Hint 17. For a full discussion of heat sinking

and thermal effects on voltage regulators, refer to the

“Regulator Thermals” section of the Designing with

Low-Dropout Voltage Regulators handbook.

4.7

Low-Voltage Operation

The MIC5209-1.8 and MIC5209-2.5 require special

consideration when used in voltage-sensitive systems.

They may momentarily overshoot their nominal output

voltages unless appropriate output and bypass

capacitor values are chosen.

During regulator power up, the pass transistor is fully

saturated for a short time, while the error amplifier and

voltage reference are being powered up more slowly

from the output (see Functional Diagrams). Selecting

TABLE 4-1:

MIC5209 THERMAL

RESISTANCE

Package

θJA

θJC

SOT-223 (S)

62°C/W

15°C/W

SOIC-8 (M)

50°C/W

25°C/W

DDPAK (U)

31.4°C/W

3°C/W

3x3 VDFN (ML)

64°C/W

12°C/W

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