MIC5233 datasheet(9/24 Pages) MICROCHIP

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DS20006033E-page 9

MIC5233

4.0

APPLICATION INFORMATION

4.1

Enable/Shutdown

The MIC5233 comes with an active-high enable pin

that allows the regulator to be disabled. Forcing the

enable pin low disables the regulator and sends it into

a “Zero” Off mode current state, consuming a typical

0.1 µA. Forcing the enable pin high enables the output

voltage.

4.2

Input Capacitor

The MIC5233 has a high input voltage capability, up to

36V. The input capacitor must be rated to sustain volt-

ages that may be used on the input. An input capacitor

may be required when the device is not near the source

power supply or when supplied by a battery. Small

surface mount, ceramic capacitors can be used for

bypassing. A larger value may be required if the source

supply has high ripple.

4.3

Output Capacitor

The MIC5233 requires an output capacitor for stability.

The design requires 2.2 µF or greater on the output to

maintain stability. The design is optimized for use with

low-ESR ceramic chip capacitors. High-ESR capacitors

may cause high-frequency oscillation. The maximum

recommended ESR is 3Ω. The output capacitor can be

increased without limit. Larger valued capacitors help to

improve transient response.

X7R/X5R dielectric-type ceramic capacitors are recom-

mended because of their temperature performance.

X7R-type capacitors change capacitance by 15% over

their operating temperature range and are the most

stable type of ceramic capacitors. Z5U and Y5V dielectric

capacitors change value by as much as 50% and 60%,

respectively, over their operating temperature ranges. To

use a ceramic chip capacitor with Y5V dielectric, the

value must be much higher than an X7R ceramic capac-

itor to ensure the same minimum capacitance over the

equivalent operating temperature range.

4.4

No-Load Stability

The MIC5233 will remain stable and in regulation with

no load unlike many other voltage regulators. This is

especially important in CMOS RAM keep-alive

applications.

4.5

Thermal Consideration

The MIC5233 is designed to provide 100 mA of contin-

uous 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 Equation 4-1:

EQUATION 4-1:

Table 4-1 shows examples of the junction-to-ambient

thermal resistance for the MIC5233:

TABLE 4-1:

5-LEAD SOT23 AND SOT-223

THERMAL RESISTANCE

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 MIC5233-3.0YM5 at

+50°C, with a minimum footprint layout, the maximum

input voltage for a set output current can be determined

as follows:

EQUATION 4-3:

The junction-to-ambient (θJA) thermal resistance for

the minimum footprint is +235°C/W from Table 4-1. It is

important that the maximum power dissipation not be

exceeded to ensure proper operation. Because the

MIC5233 was designed to operate with high input

voltages, careful consideration must be given so as not

to overheat the device. With very high input-to-output

voltage differentials, the output current is limited by the

total power dissipation.

Package

θJA Recommended

Minimum Footprint

SOT23-5

235°C/W

SOT223

50°C/W

PDMAX



TJMAX



–



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





Where:

TJ(MAX) = Maximum junction temperature of

the die at +125°C

= The ambient operating temperature

θJA

= Layout dependent

VIN VOUT

–

I

OUT

VIN

IGND



PDMAX



125

C 50C

–

235

C/W

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





Where:

PD(max) = 319 mW

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