MIC5205-2.5YM5 View Datasheet(PDF) - Micrel

Part Name

Description

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MIC5205-2.5YM5

150mA Low-Noise LDO Regulator

Micrel 

Micrel

Application Information

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 1.

Input Capacitor

A 1µF 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.

Reference Bypass Capacitor

BYP (reference bypass) is connected to the internal

voltage reference. A 470pF 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 2.2µF or greater are generally required to

maintain stability.

The start-up speed of the MIC5205 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.

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. 1.0µF minimum is recommended

when CBYP is not used (see Figure 2). 2.2µF minimum is

recommended when CBYP is 470pF (see Figure 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 1MHz. Ultra-low-ESR 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 required for output stability. The capacitor

can be reduced to 0.47⎧F for current below 10mA or

February 2006

MIC5205

0.33µF for currents below 1mA.

No-Load Stability

The MIC5205 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.

Thermal Considerations

The MIC5205 is designed to provide 150mA 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:

( ) PD(max) =

TJ(max) − TA

θ JA

TJ(max) is the maximum junction temperature of the die,

125°C, and TA is the ambient operating temperature. θJA

is layout dependent; Table 1 shows examples of

junction-toambient thermal resistance for the MIC5205.

Package

θJA

θJA Square

θJC

Recommended Copper Clad

Minimum

Footprint

SOT-23-5(M5)

220°C/W

170°C/W

130°C/W

Table 1. SOT-23-5 Thermal Resistance

The actual power dissipation of the regulator circuit can

be determined using the equation:

PD = (VIN – VOUT) IOUT + VIN IGND

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 MIC5205-3.3BM5 at

room temperature with a minimum footprint layout, the

maximum input voltage for a set output current can be

determined as follows:

PD(max)

=

(125°C − 25°C)

220°C/W

PD(max) = 455mW

The junction-to-ambient thermal resistance for the

minimum footprint is 220°C/W, from Table 1. The

maximum power dissipation must not be exceeded for

proper operation. Using the output voltage of 3.3V and

an output current of 150mA, the maximum input voltage

can be determined. From the Electrical Characteristics

table, the maximum ground current for 150mA output

current is 2500µA or 2.5mA.

455mW = (VIN – 3.3V) 150mA + VIN·2.5mA

455mW = VIN×150mA – 495mW + VIN·2.5mA

950mW = VIN×152.5mA

8

M9999-020806

(408) 955-1690

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