MIC5212-SJBM Datasheet MIC5212-SJYM, MIC5212-SJYM-TR, MIC5212-SJBM-TR | P7-P9

April 2003 7 MIC5212

MIC5212 Micrel

Applications Information

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.

Output Capacitor

An output capacitor is required between OUT and GND to

prevent oscillation. 1.0µF minimum is recommended. Larger

values improve the regulator’s transient response. The out-

put 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 may cause a low-

amplitude oscillation and/or underdamped transient response.

Most tantalum or aluminum electrolytic capacitors are ad-

equate; film types will work, but are more expensive. Since

many aluminum electrolytic capacitors have electrolytes that

freeze at about –30°C, solid tantalum capacitors are recom-

mended 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

0.47µF for current below 10mA or 0.33µF for currents below

1mA.

No-Load Stability

The MIC5212 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.

Dual-Supply Operation

When used in dual supply systems where the regulator load

is returned to a negative supply, the output voltage must be

diode clamped to ground.

Power SO-8 Thermal Characteristics

One of the secrets of the MIC5212’s performance is its power

SO-8 package featuring half the thermal resistance of a

standard SO-8 package. Lower thermal resistance means

more output current or higher input voltage for a given

package size.

Lower thermal resistance is achieved by joining the four

ground leads with the die attach paddle to create a single-

piece electrical and thermal conductor. This concept has

been used by MOSFET manufacturers for years, proving

very reliable and cost effective for the user.

Thermal resistance consists of two main elements, θ

(junction-to-case thermal resistance) and θ

(case-to-ambi-

ent thermal resistance). See Figure 1. θ

is the resistance

from the die to the leads of the package. θ

is the resistance

from the leads to the ambient air and it includes θ

(case-to-

sink thermal resistance) and θ

(sink-to-ambient thermal

resistance).

printed circuit board

ground plane

heat sink are

SO-8

AMBIENT

Figure 1. Thermal Resistance

Using the power SO-8 reduces the θ

dramatically and

allows the user to reduce θ

. The total thermal resistance,

(junction-to-ambient thermal resistance) is the limiting

factor in calculating the maximum power dissipation capabil-

ity of the device. Typically, the power SO-8 has a θ

20°C/W, this is significantly lower than the standard SO-8

which is typically 75°C/W. θ

is reduced because pins 5

through 8 can now be soldered directly to a ground plane

which significantly reduces the case-to-sink thermal resis-

tance and sink to ambient thermal resistance.

MIC5212 Micrel

MIC5212 8 April 2003

Low dropout linear regulators from Micrel are rated to a

maximum junction temperature of 125°C. It is important not

to exceed this maximum junction temperature during opera-

tion of the device. To prevent this maximum junction tempera-

ture from being exceeded, the appropriate ground plane heat

sink must be used.

100

200

300

400

500

600

700

800

900

0 0.25 0.50 0.75 1.00 1.25 1.50

COPPER AREA (mm

)

POWER DISSIPATION (W)

40°C

50°C

55°C

65°C

75°C

85°C

100°C

Figure 2. Copper Area vs. Power-SO

Power Dissipation

(∆ (∆

(∆T

)

Figure 2 shows copper area versus power dissipation with

each trace corresponding to a different temperature rise

above ambient.

From these curves, the minimum area of copper necessary

for the part to operate safely can be determined. The maxi-

mum allowable temperature rise must be calculated to deter-

mine operation along which curve.

∆T = T

J(max)

– T

A(max)

J(max)

= 125°C

A(max)

= maximum ambient operating temperature

For example, the maximum ambient temperature is 50°C, the

∆T is determined as follows:

∆T = 125°C – 50°C

∆T = 75°C

Using Figure 2, the minimum amount of required copper can

be determined based on the required power dissipation.

Power dissipation in a linear regulator is calculated as fol-

lows:

= (V

IN1

– V

OUT1

) × I

OUT1

+ V

IN1

× I

GND1

+ (V

IN2

– V

OUT2

) × I

OUT2

+ V

IN2

× I

GND2

With a common 5V input, a 3.3V, 300mA output on LDO 1 and

a 2.5V, 150mA output on LDO 2, power dissipation is as

follows:

= (5V – 3.3V) × 300mA + 5V × 5mA

+ (5V – 2.5V) × 150mA + 5V × 1.8mA

= 0.919W

From Figure 2, the minimum amount of copper required to

operate this application at a ∆T of 75°C is 500mm

Quick Method

Determine the power dissipation requirements for the design

along with the maximum ambient temperature at which the

device will be operated. Refer to Figure 3, which shows safe

operating curves for three different ambient temperatures:

25°C, 50°C and 85°C. From these curves, the minimum

amount of copper can be determined by knowing the maxi-

mum power dissipation required. If the maximum ambient

temperature is 50°C and the power dissipation is as above,

920mW, the curve in Figure 3 shows that the required area of

copper is 500mm

The θ

of this package is ideally 63°C/W, but it will vary

depending upon the availability of copper ground plane to

which it is attached.

100

200

300

400

500

600

700

800

900

0 0.25 0.50 0.75 1.00 1.25 1.50

COPPER AREA (mm

)

POWER DISSIPATION (W)

85°C 50°C 25°C

= 125°C

Figure 3. Copper Area vs. Power-SO

Power Dissipation (T

)

April 2003 9 MIC5212

MIC5212 Micrel

Package Information

45°

0°–8°

0.244 (6.20)

0.228 (5.79)

0.197 (5.0)

0.189 (4.8)

SEATING

PLANE

0.026 (0.65)

MAX)

0.010 (0.25)

0.007 (0.18)

0.064 (1.63)

0.045 (1.14)

0.0098 (0.249)

0.0040 (0.102)

0.020 (0.51)

0.013 (0.33)

0.157 (3.99)

0.150 (3.81)

0.050 (1.27)

TYP

PIN 1

DIMENSIONS:

INCHES (MM)

0.050 (1.27)

0.016 (0.40)

8-Pin SOIC (M)

MICREL, INC. 1849 FORTUNE DRIVE SAN JOSE, CA 95131 USA

TEL + 1 (408) 944-0800 FAX + 1 (408) 944-0970 WEB http://www.micrel.com

The information furnished by Micrel in this datasheet is believed to be accurate and reliable. However, no responsibility is assumed by Micrel for its use.

Micrel reserves the right to change circuitry and specifications at any time without notification to the customer.

Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can

reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into

the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchaser’s

use or sale of Micrel Products for use in life support appliances, devices or systems is at Purchaser’s own risk and Purchaser agrees to fully indemnify

Micrel for any damages resulting from such use or sale.

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MIC5212-SJBM

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MIC5212-SJBM

MIC5212-SJBM

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