MIC3490 datasheet(9/20 Pages) MICROCHIP

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 2019 Microchip Technology Inc.

DS20006137A-page 9

MIC3490

4.0

APPLICATION INFORMATION

4.1

Enable/Shutdown

The MIC3490 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 MIC3490 has a high input voltage capability, up

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

voltages that may be used on the input. An input capac-

itor 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 MIC3490 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 dielec-

tric 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 capacitor to ensure the same minimum

capacitance over the equivalent operating temperature

range.

4.4

No-Load Stability

The MIC3490 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 MIC3490 is designed to provide 100 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 Equation 4-1:

EQUATION 4-1:

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

thermal resistance for the MIC3490:

TABLE 4-1:

5-PIN SOT23 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 MIC3490-3.0YM5 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:

Package

θJA Recommended

Minimum Footprint

SOT23-5

+235°C/W

PDMAX



TJMAX



–



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





Where:

TJ(MAX) = Maximum junction temperature of

the die at +125°C

TA =

The ambient operating temperature

θJA =

Layout dependent

VIN VOUT

–

I

OUT

VIN

+IGND



PDMAX



125

C50C

–

235

C/W

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





Where:

PD(MAX) = 319 mW

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